Never Connect Your Vacuum Advance to Ported Vacuum!

[@roaddog1973]

Have run it both ways, and it's noticebaly better on ported for my car. I'd advise anyone to try it both ways on their vehicle and just choose the one that seems to work best.

[@chiefexecutive]

Yep!

[@whiteboyfromernul]

Agreed,mine runs like a dog on manifold and awesome on ported

[@Robett-r4l]

​@@whiteboyfromernulfor your vacuum advance to work it has to be vacuumed open with throttle. At idol you don't have vacuum advance if you're using a ported vacuum. With a ported vacuum you get advanced timing when you give it throttle. With a manifold vacuum you have already advanced your timing all the way so when you give it throttle it's slower to get speed then if you use a ported vacuum.

[@whoeverwhatever9279]

Probably have a stock engine. Or already enough initial

[@Numer1Polak]

more than likely you are tuned rich at idle/part which would explain why it does.

[@ThunderHead289]

Yeah no offense but i think there is a good learning opportunity here and ill lay it on ... The lean rich thing is a fat misnomer thats been perpetuated on the internet forever, it plays in maybe 5 percent - the biggest factor is throttle position, this is why vacuum advance is dependant on engine load NOT afr. Light throttle, lower cylinder pressure, longer flame propogation time due to less dense charge (charge volume vs cylinder volume), needs more advance to fully ignite the mixture at the right time. High load is the exact opposite. Ever heard of "boost retard" where we pull timing due to cylinder psi? Same concept. Its presented as rich vs lean because thats easy to understand - turn your mix screws to 11:1 afr at idle vs 14:1, timing largely doesnt care. It plays in maybe 5 percent. Heres why ported vacuum shines (again as you show, its the same as manifold except at idle) - got a mild cam blipping the vacuum advance threshold at idle? Now you have variable timing at idle, hanging rpm, overall not good. Take an aftermarket hei - they all have 15 degrees of mechanical advance roughly, and 15 degrees of available vacuum advance. Okay, so cool we set it at 8 degrees initial. We add the 15 manifold at idle, cool we have 22-23, not bad. BUT WAIT, now we stand on the gas - our timing drops too low because we biased it low to accomodate manifold vacuum, and we now only have 22-23 degrees of total timing at high load. We just left a PHAT amount of power on the table. Better off running ported, running 15-18 degrees of mechanical advance which gives you good cruising advance and good total timing. This is but one of many examples i have as to why you shouldnt run manifold advance. Ported timing IS NOT about the vacuum advance - the advantage lies in what it allows you to do with your mechanical timing. Thunderhead289 - engineer

[@pacbrian3809]

this ends the entire discussion. but its a great clickbait video

[@thejunkyardnecromancer]

You are right. I described the mixture density as lean and rich when I should have used less dense and more dense. I'm going to put this all to the test in my follow up! I'd love to pick your brain on your tuning methods at some point so I don't misrepresent them in the follow up.

[@newguysgarage6802]

Well well well 😂 This sounds extremely similar to a video SOMEONE made as a response to yours dosnt it Junkyard 😏 kzbin.info/www/bejne/rZfdiaB4gNCrjLM Me and Junkyard have been going back and forth on this topic lol, we are good buds though 😁

[@thejunkyardnecromancer]

@@newguysgarage6802 I'll prove you wrong! Although, I will be the bigger man and admit if I prove myself wrong. XD

[@ThunderHead289]

​@thejunkyardnecromancer I'm not here to fight back and forth with like minded folks, but you can't post a video with a thumbnail of my or uncle Tony's face stating we're wrong without one of us rolling in 🙂

[@MarcBchannel]

There are so many different engine combos that I dont think there is one answer to all. It all depends on the combo and how your distributor is curved. Cammed vs stock, heavy vs light, auto vs manual, cruise rpm and gearing. You have to optimize for any given combo and give your engine the timing it wants. One thing to keep in mind is that the vacuum advance is for fuel economy at cruise and it should be tuned for that purpose. Use an adjustable vac adv can. At a cruise, the optimal timing can be 40+ degrees btdc. Also, there is a gap between initial advance and mechanical advance and the vacuum advance fills in the gap. The initial timing and how the vacuum and mechanical advance fill in that gap will affect acceleration and response. Another note on heavy vehicles with tight torque converters is that when using manifold vac you have to run a lower initial timing to idle in gear. If you have a stock distributor with a lazy mech adv, WOT acceleration off the line might suffer due to the gap between intitial and mech adv when the vac adv drops out at wot. There can be cases made for either or. Cheers

[@timothyarnott3584]

I was gonna comment, but i saw your reply, and i cudnt agree more, it all depends on the specifix combo your workin with, my shop uses ported for most apps, but we HAVE used manifold in a few cases......all depends on combo.....nicely written comment!!!

[@MarcBchannel]

@timothyarnott3584 Ya ported works good. Having a tunable pot is good to dial it in. Best thing is to figure out what your engine wants for timing under different operating conditions and dial it in for your specific combo 👍

[@Nomadcreations]

Yes Good points also. Each Engine (Cam, Exhaust, carb Condition,Driving Style) Makes so Either Hose Placement has a 1-Only True Rule, Trial On error testing For Each Driver is What it takes

[@terryzeissler4199]

As a 50 year auto tune up and diagnostic specialist I disagree with you. Manifold vaccuum at idle will cause many engines to misfire causing unburned fuel to go out the tail pipe. I have had to reroute some cars to ported because the idled so badly. What you are missing is the fact that purpose behind vaccuum advance from ported is that it is there to provide the extra advance at cruise to improve fuel economy under light loads. As loads increase and you open the throttle more the amount of advance decreases in proportion to the load to prevent detonation. If you want to see the increased emmissions from manifold advance you need to use a four gas analyser. Yes emission requirements did help to el;eiminate manifold vaccuum, but saying this is wrong is like saying the PCV system is inferior to the draft tube that used come off the intake manifold and dump all the crankcase fumes directly into the atmosphere. You might also believe that the EGR system is bad when what it does is control combustion temperatue to prevent NOX production and has zero effect on performance or mileage. I have actually seen burnt pistons and valves because some car owner stuck a ball bearing in the EGR hose and created detonation and too hot of combustion gases going out the exhaust valve. In the mid 1970s to the mid 1980s it was thought the smog was caused by hydrocarbons and some of the crazy things they did such as 18:1 AFR was actually creating more smog and it took them many years to finally realize that photo smog was caused by oxides of nitrogen. Nitrogen is normally inert and does not combine with other gases except in the enclosed combustion chamber with high heat of combustion and the even higher heat of too lean a mixture. The 14.7 to 0ne ratio we see today at idle and cruise was found to produce the lowest emmisions of HC, CO2, CO, and NOX. tipping leaner causes an increase in NOX as well as HC from misfires. Going richer causes an increase of CO and CO2, the increased CO because of insufficient oxygen to completly form CO2. Back to ported vs manifold in relation to performance, at wide open throttle the are both zero and your power comes from your mechanical advance curve and total timing, vaccuum advance is completly out of the picture. if you want to dive deeper into the history behind the emission history and reasoning, one of my favorite automotive technical authors is William H. Crouse. He wrote many text books in the 1950s, 60s, and 70s dealing with engine tuning, emissions, tune up and electrical. Much of my training on all this was thru Sun Electric and Allen Test products for whom I also did training for on diagnostics and the use oscilliscopes and gas analysers in the 1980s.

[@thejunkyardnecromancer]

I'll see if I can find those text books! I understand that ported vacuum is the same as manifold vacuum except at idle. My argument is that you need that extra advance at idle. I'm going to do a follow up and test both ways. I'm willing to be wrong, but I'm going to put it to the test.

[@dezford5408]

Is for trying to educate theese youngsters. He just doesn't understand the original design.

[@Bluephrog]

@@thejunkyardnecromanceryou ask about ported and manifold vacuum being the same except at idle. Thunder289 actually has a video showing this correlation. No one has yet described why! High vacuum means lower cylinder pressure slower burn. This means more ignition advance to have the main burn at the correct degrees just after TDC to get the most power. Open the throttle plates and the mixture goes rich as well as cylinder pressure goes way up. Going rich and high cylinder pressure means faster burn. Fast burn means you need later timing to keep the burn at the correct degrees just after TDC for max power. If you advance the timing at this point you risk pinging and poor performance, burn hits before TDC. Ported vacuum does exactly that, advances timing. Manifold vacuum retards timing at this point preventing pinging and deliver max power. It can take some time to get the mechanical advance in sync with vacuum advance for the most power, best fuel economy and best tune. Of course you can detune, richen up the idle, set your mechanical timing at idle for best idle and use ported vacuum.

[@roberta.6399]

​@@thejunkyardnecromancerported vacuum goes up as throttle opens, manifold vacuum goes down as throttle opens.

[@thejunkyardnecromancer]

@@roberta.6399 no. Ported vacuum and manifold vacuum are identical when you open the throttle. I have a short demonstration this, and TH289 has also demonstrated this in the past. The only difference is when the throttle is closed.

[@OwensGarage]

I ran my 318 on manifold vacuum for a while, throttle response was TERRIBLE. Switched it to ported vacuum and it’s like driving a different truck. That’s just my experience…

[@thejunkyardnecromancer]

Very interesting

[@MarcBchannel]

Your distributor probably didn't have enough mechanical advance or a lazy mechanical advance curve so the ported advance helped fill in the gap off idle til your mech adv kicked in 👍

[@OwensGarage]

@@MarcBchannelyeah you’re probably right. It’s an 80’s “smog” distributor…. I really should get one with a more aggressive mechanical advance but what I have is working so I haven’t spent the money yet.

[@anthonyjulson8840]

Yeah I had the same issue you did. Same engine even! I hooked the vacuum to the carb, and it was mint!

[@zombezoo]

Same here. 73 318. Vacuum advance connected to manifold vacuum and it ran terrible. This may work for some vehicles but not mine.

[@sagepope731]

I experimented with both on my truck being a non emissions motor from the factory and found my truck seemed happier with manifold

[@thejunkyardnecromancer]

Since you experimented with both, what was your experience with each as far as throttle response and driveability?

[@sagepope731]

@@thejunkyardnecromancer On ported vacuum it ran a lower idle speed and you could feel it pull into the advance more, but seemed to require a little more throttle to get goin, whereas on manifold it felt more driveable using slightly less throttle for the same results. This is a bone stock 350 with 2.02/1.71 valves. It very rarely hits 200 degrees and while towing up the pass over 90 only ever hit 210 maintaining 55mph at 2800 rpm. it is easier getting over hills as well. I do need a different carb as the 600 is choking it out a bit, but otherwise drives perfectly fine. The old timer that owned it had it on manifold and he's been around the block more than I have so I trust his judgment on the matter more than what standard is

[@playstation2bigs]

"Carburetor" the never ending saga

[@alltime4417]

Ported vacuum works, in conjuction by design, with a type of temperature device that switches from manifold to ported. Its that 3 way hose thingamajog. For easier starting and engine cooling at idle. Smoake and. Tires

[@72chevelle156]

for those that commented it's the build of the engine, it's not the build of the engine, it's the vac canister. going from port to manifold vacuum requires a different vac canister make sure your vacuum adv canister is all in at idle or your idle will be erratic since vacuum is just a touch bouncey and gets more so with performance engines. it takes some research to get the right canister that is full adv at idle and doesn't have too much advance. you will exceed what is called total advance (initial + mechanical) don't lower your initial advance and when you reconnect your canister after tuning you will need to bring the idle down (close throttle plate) which will help if you have run on or diesel when you shut off engine. also, this topic is why many hot rods overheat in traffic. BTW utg thinks manifold vac drops the timing below initial and he thinks ""why would you want to drop timing when you take off from a stop?" so he evidently sets timing with the canister connected. which defeats the purpose. but i used to think the same way.

[@thejunkyardnecromancer]

Well said good sir.

[@GenasysMech]

You're right about the manifold vacuum but wrong about the solenoid throttle advance, it's used to compensate for the drag of an A/C compressor cutting in.

[@richardbeals1403]

Its simply a difference in how the engine tune is set up. Both can work exactly the same depending on how your initial timing is set and your advance curves.

[@thejunkyardnecromancer]

You can definitely time your engine to run on either one, but I would argue manifold vacuum is the better option.

[@newguysgarage6802]

Your almost right in the money, just one key difference though. When you hit the gas with manifold vaccum it takes timing away When you hit the gas with ported it will add timing So if you want to run 22° initial advice, with manifold when you punch it it will drop the timing down when you need it the most If you run 22° initial machanical, then when you punch it it will add timing or keep it the same at WOT so you can keep your timing giving you the grunt you need off the line 😉

[@thejunkyardnecromancer]

@@newguysgarage6802 I explained that exact thing in the video. When you punch it, you actually don't need as much timing as you think!

[@richardbeals1403]

@@newguysgarage6802Revving an engine in neutral isnt even remotely the same as an engine under load. An engine under load make very little vacuum and at wide open throttle there is no vacuum. Ported vacuum is nothing but manifold vacuum that is switched through the throttle blades, once you are off idle, the ported and manifold are the same. And guess what happens if you are running low initial with your vacuum advance hooked to manifold? All that timing that was pulled in at idle manifold vacuum instantly disappears. As I said, it is simply a difference in the way the engine is tuned.

[@dannymccarty344]

@@richardbeals1403 I think you would bennefit by honing your comprehension skills. Dont just ignore the facts. Maybe watch the video again. Try to understand what he's saying.

[@angryyankee9184]

Simple question. Then why does MSD literally say 'the vacuum line should be routed to a ported vacuum outlet' on the very first page of instructions for their distributor?

[@thejunkyardnecromancer]

Could be that their distributors come from the factory set up to run on ported vacuum. I feel like I saw a video from MSD that said otherwise. Let me see if I can find it. Found it! This is an official MSD video explaining how ignition timing works. When he talks about vacuum advance he says to connect it to full vacuum. He also explains on engines with blowers that you need to plug the vacuum advance into a vacuum port below the blower. Video: kzbin.info/www/bejne/o6SrnZagp9OdjJIsi=gxjjqikkYtVq73qx

[@kwasg3]

Well I watched to see how many fallacies you had in this. ALOT. You are 180 wrong and using logic errors to explain it. First, you are confusing load with lean and rich correlation. You are ignoring cylinder pressure, and you are ignoring that there is more than one type of port vacuum, in addition to manifold vacuum. Your model of what is happening is so woefully simplistic it is invalid. Cylinder pressure has dramatically more effect on flame front then rich/lean, and one reason EGR is used because in theory it is very close to an inert gas that takes up space without affecting AFR. Tuning modern fuel injection, the major inputs into the equation is engine speed and load for spark timing. I suggest you plug in two vacuum gauges, and go for a drive to see what really is happening on those two types of vacuum signals, because no load running is nearly irrelevant in the big picture. If you are on the correct port vacuum, you will have a clearer understanding why part throttle light load generates proper timing advance for much more fuel efficiency and much less pollution.

[@PsalmFourteenOne]

Yup. I noticed that as well. As for idle I usually use ported. It makes a more throaty low idle without the manifold advance. And as many pointed out... as soon as you barely crack the throttle blades the ported connection has the same vacuum as manifold. The blades just block the ported connection at idle stop. Pull the hose and set your base advance... engine performance is exactly the same no matter which port you use. Only idle is altered.

[@bud122469]

@@PsalmFourteenOneno engine performance isn’t exactly the same! Most vehicles with a distributor will have a stumble and possibly be hard to start when vacuum advance is hooked to manifold vacuum! Fixed many vehicles over the years that had those issues!

[@jamessignorelli852]

Thank you , you saved me quite a bit of typing

[@peterphillips1493]

Yes sir, efficiency goes hand in hand with pollution.

[@skydive9955]

Wow, you completely forget the initial timing event and how radical advancing timing with manifold vacuum and the effects on idle and detonation. In theory you get the same results with cylinder pressure on either port. Nice try young man but the ported vacuum for advance is correct on most applications in that era..

[@user-lh2yr2sk4o]

Wonder why Pontiac advised you to disconnect the distributor when setting initial timing? Always had vacuum to the distributor. Makes sense to me to have extra timing at idle and cruise speeds. Don't want it under hard acceleration.

[@joeseda8102]

So it seems that manifold vacuum is better if you have your initial timing set by physically advancing or retarding the distributor for best idle. Just don't forget to add the amount of distributor advance at idle to avoid detonation when vacuum advance reaches maximum advance. Ported vacuum seems to work best if you have the distributor properly calibrated for when manifold vacuum starts to drop. You can manually retard initial idle timing as necessary to prevent detonation. I normally connect carb to ported vacuum, accelerate the engine to 3k rpm, manually advance the distributor until engine starts to miss, and then back off 4 degrees at the distributor and lock it down. Full distributor advance is normally in by 3k rpm in production vehicles. You can also check with the vacuum gage at what rpm vacuum starts to go down and adjust the numbers accordingly. Never had any trouble with detonation or sputtering during acceleration on any of my vehicles using this method and they smoothly accelerate to full power.

[@jebdepaiva960]

I get your logic, but I've ran into 2 issues using manifold vacuum. 1) In a car with an auto trans it creates a larger spread in RPM between park/neutral into drive/reverse which makes it kick violently when putting into gear. It's due to the difference in vacuum and timing between park/neutral and drive/reverse. 2) In driving scenarios where your car bogs, it usually stalls. That's because when rpm drops below idle, vacuum and timing drops too resulting in a further drop in rpm.

[@thejunkyardnecromancer]

@@jebdepaiva960 that is interesting. My daily driver has a manual transmission so I don't experience this stuff. I'm currently working on my blue F250 which has an automatic. So I'll have to test this out. Thank you!

[@jebdepaiva960]

@@thejunkyardnecromancer I've been thinking it may be fixable by limiting the can's travel so it's "all in" a couple in/Hg lower than my manifold vacuum. We'll see.

[@slednfool]

I feel like you have the lean/rich faster/slower thing backwards. Your engine will ping if your mixture is too lean, it pings because it burns faster than a correct richer mixture. You might be right but I dont think your theory is correct.

[@thejunkyardnecromancer]

Hmm... I've never heard of a lean mixture causing pinging. Only ever heard of too much advance (maybe from too much initial timing or mechanical/vacuum advances tuned incorrectly), or heat soak causing pre-ignition and pinging. Time for me to do some research!!!

[@mk-xg2kt]

You are absolutely right. and quite easy to prove (not now). and think about why the car makers would choose a worse alternative when everything was allowed. the difference is only around idle( smal throttle opening). and when the ported vacuum is open, the difference ends. and what is the most powerful idle ignition. try increasing and decreasing the ignition at idle. so you get different idle speeds, the highest speed is the most efficient (most hp). then the expansion has taken place at the best position in relation to where the piston is located. exactly the same as when you have wot ,so it likes a certain ignition. and then the vacumcanister has no meaning because it does nothing then.

[@morgansword]

This old man has his eyes opened up to something so obvious now to me as I started wrenching in early sixties and yes we use the manifold for our vacuum advance. As time went by, I fell into the carb theory also but had troubles tuning out for max power and good throttle response. I am too crippled up to go play now on engines but I do see the argument for both sides... I see it as a idle jets problem and how much power with right or wrong jets making a ton of difference. I there for think maybe think if your not getting what you like or feel out of a engine, try the other for best running performance because of engine designs and if its fuel injected or carbureted.

[@thejunkyardnecromancer]

Definitely! I think hotroding and building old vehicles requires some experimentation to find the right combo for you!

[@MoparDonny]

Since this video has been made, you think he knows how the system actually works yet? You “can” set things up to run on manifold vacuum, but not usually. Ported Vacuum IS the correct setup. Try both ways and notice the difference

[@thejunkyardnecromancer]

@@MoparDonny I'm working on a follow up where I test everything. I ended up going down a long rabbit hole and it's taking longer than expected haha. I was definitely wrong about some things and right about others!

[@edwardpurks3883]

I like this topic. The only difference between the two methods is this: Manifold vac connection provides extra vacuum advance at idle. Ported vac connection waits until you touch the gas pedal before it adds the SAME extra vacuum advance. Performace, fuel economy and driveablitiy are identical for both methods above idle. Benifits of manifold Vac are smoother idle, cooler engine temps idling, better vac signal to carb and power brakes while at idle. This also lowers noise from the exhaust while idling. It provides faster starting. This works great on stock and modified engines. Engines with big cams need this extra timing at idle just to make them streetable. Switching methods only takes a few minutes but does require readjusting idle speed and idle mixture screws. Such a debate of something only effecting idle

[@stuckinmygarage6220]

I think I agree, except regarding power brakes. Boosters are connected to base, after Venturi. There is always vacuum present.

[@edwardpurks3883]

@stuckinmygarage6220 Yes, brake boosters are connected to full manifold vacuum, but you are thinking about it the wrong way. When you add the extra timing at idle from vacuum advance being connected manifold vac, your engine produces noticeably more vacuum while idling. Even at the same idle speed as before. Now you have more vaccum assist to all your vacuum powered functions. My engine went from 15in vac at idle to 21in. Same idle rpm

[@roccoloops]

Very well said 👏 It always amazed me how many people got their knickers in a twist for something that follows literally the exact same curve apart from idle. I've personally always ran manifold because in both my stocker and my bigger cam weekend cruiser they enjoy the ease of starting at such a nice 'starter-motor friendly' 6deg BTDC before the engine fires and manifold vac adv shoots that up to a steady ~20deg BTDC and I enjoy all the benefits of nice idle characteristics, cooler running temps and sharp throttle response.

[@stuckinmygarage6220]

@edwardpurks3883 Thank you, Mr. Purks, for your comment. However, I did not 'think about it the wrong way'. I agree with everything you said, except that there is no comma between "carb and power brakes". There is no 'better' vacuum for power brakes. It's constant manifold. Ported has no effect on brake boosters. [Off topic, unless talking about leaking diaphragm or something.] Again, I agree with your well written comments. Best regards

[@edwardpurks3883]

@stuckinmygarage6220 Hmm. You still don't understand how increased engine vacuum improves vaccum powered brake assist. More timing at idle doesn't just increase vacuum single to the carb, but it increases vacuum signal to the entire intake manifold. Including the line feeding the brake booster. Everything will see a higher vacuum signal with the increased timing. You can also feel increased brake booster assit just from your engine decelerating(which increases vacuum temporarily). The brake pedal goes noticeably further down if you Rev your engine, then let it decelerate. You can witness this sitting still in Park or neutral. I appreciate the comment. Running more timing at idle helps booster signal too. Especially just idling around a parking lot or driveway

[@richardtramell5574]

I’m not getting in a argument. I set mine up manifold. Just for shits ang giggles set it on on ported (readjusted everything) shit it ran better.

[@mrkultra1655]

How about this. If you have a pre-emissions engine, (unless it’s some wild worked over dedicated hot rod) hook it up the way the engineers intended as reflected in the factory service manual, tune your idle circuit, transition circuit, and wide open throttle PROPERLY, and don’t worry about it. Some engines were one way, others were another way, it all really depends on what you have. Pour over all the original manuals that you can find. They are a wealth of information that we are quickly losing. Anyone else out there know that a lot of the early voltage regulators were adjustable? Probably not. Ford used them right up to the time that they switched to electronic ignition. Got luck finding one, and the aftermarket sure as hell don’t make ‘em. It’s really important to make sure your electrical is spot on to make sure your ignition is spot on, before you even think about timing and carburetor adjustments.

[@thejunkyardnecromancer]

You are right! I have shop repair manuals for all my vehicles and reference them religiously. A problem does arise however when you modify something, especially removing emissions equipment like EGR, or installing better flowing intake, exhaust, and carb.

[@dale116dot7]

It depends on what the engine wants for idle timing and combustion stability. Sometimes the timing retard is required to raise the cylinder pressures at idle especially if the mixture is not overly diluted from overlap-induced internal EGR. Retarding the timing using ported vacuum means you need more throttle opening at idle which allows a bit more air when compared with residual gas. I’d say pick whichever the engine wants. Also one other thing, the more retarded timing will pull less a bit less oil through the valve guides at idle since the manifold vacuum will be a bit lower. For EFI engines timing at idle is often a bit retarded, but there is effectively an inverted ‘mechanical’ advance below idle speed. This will advance the timing if you lug the engine a bit without moving the throttle, the timing advances, engine torque goes up, and the engine is nice and stable while lugging. The timing retards as RPM picks up, giving a nice smooth lugging response, even without moving the throttle. Think of the mechanical timing with a ‘V’ advance curve with the tip of retard just above the desired idle speed.

[@andrewhill1415]

Not when the engineers were concerned about emissions and you’re concerned about power and efficiency.

[@AimlessMoto]

Ported = better idle. Manifold = bad idle. Tried a thousand different ways, always the same result. You don't want the advance coming into play at idle.

[@PickinwithPickle]

Lol 😂 You literally made a Canadian version of Dan! 🤣 #manifoldvacuum!

[@thejunkyardnecromancer]

The MN accent and Canadian accent are similar kinda haha. #manifoldvacuum!

[@6percentrecycled]

I also detected a little Slymo slipping in there😀

[@crazycaseyscustoms]

You’re an intelligent dude, and you’ve probably given this more thought than me, but you don’t seem to talk about the effect of load in this equation. Most of the stuff I deal with is carbureted V8 engines with some camshaft, in vehicles that are on the heavier side (kinda like UTG and Thunderhead 289 too, right?). I typically have plenty of base timing at idle, and a relatively fast advance curve, but that little bit of advance off idle with ported vacuum seems to play nicely with a not-too-huge accelerator pump shot to get the vehicle to move out well without blowing a bunch of unburnt fuel out the exhaust. To make that same engine work on manifold vacuum, I’d have to lower my base timing, increase my pump shot, and add more mechanical advance, faster. I think it would wind up being a dog…

[@thejunkyardnecromancer]

Possibly! I am testing all this right now to see which is better (video coming soon!). If I can ask, how far advanced do you give works best on your engines? I know Dan had his set up near 20° BTDC before he just locked out his distributor. Thanks for commenting!

[@yeboscrebo4451]

Higher load is a more densely packed cylinder which negates the need for the advance timing from the vacuum canister. You wouldn’t need to lower base timing but yes you would need to increase your pump shot and make sure the mechanical is coming in fast and strong. Just my opinion because that’s exactly what I had to do on my f350 which almost doubled its mpgs and runs much cooler and quieter after the switch to manifold timing

[@mustangeroo]

I’m a manifold vacuum guy. The ported guys almost got me but David Vizard is a manifold guy too. He knows.

[@brawler1997-v6t]

I ran ported once man car overheated smelled nasty exhaust was leaking ... Manifold the way to go cars runs better does not smell runs cool

[@iancoachwerksllc]

Andy at "Unity Motor Sports" has some good videos on this subject. He runs manifold vacuum on his N/A 700hp 427 with dual carbs.

[@gearheadted9210]

In my experience throttle response suffered on manifold,opening the throttle instantly retards the timing,not good,of course not all engines and setups are the same,getting base and WOT timing set correctly is first order,dial timing light is essential,Ive spent days super tuning

[@thejunkyardnecromancer]

That's what some other people have said too. I'm going to test both configurations in my follow up video.

[@gregsmith332]

One thing these three have in common is that they share a deep, seething, misguided hatred for fuel injection. To them, it's carburetors or nothing.

[@thejunkyardnecromancer]

That is very true.

[@mikegreer9041]

Manifold vacuum allows better control of advance at low rpms. When you stomp the throttle you lose vacume until rpms come up. When that happens it retards the timing until the rpms come up to prevent spark knock.

[@davenkaren2572]

Absolutely perfect explanation!! Subscribed!!

[@nicholasagnew2792]

...and for that reason alone your engine can have a stumble that connecting to ported vacuum will fix.

[@duanegray8620]

So I have a stumble at 45mph. 351w HEI dizzy Manifold vacuum connected 2bbl Holley Stock internals If I pull the vacuum advance line and plug it, It runs better? I wanted to connect it to ported vacuum but after watching this maybe my timing is off ?

[@robertclymer6948]

How does vacuum retard timing? don't it pull to advance but does not push to retard? hmmmmmm Glad I got mechanical advance MSD dizzy. lol

[@ejscarfo]

There is no right or wrong answer to this. It will depend on your situation and the original design of your car and its engine. For example, I have a 70 Nova with a crate 350 engine in it. That engine has provisions to have emissions on it, it has an EGR port in the head. I’ve run it both ways and it runs best with ported vacuum. Now, if the car has an original 350 from the factory in 1970, that particular motor would have had a modulated ported vacuum advance setup controlled by a solenoid. So in essence, it was like ported vacuum.

[@Volfandt]

Being old school, I cut my teeth in auto wrenching by always hooking the dist to ported vac. Even my 49 Chevy's 216 & now 235 came factory connected to ported vac. But now I've seen the light, LOL.... I read where manifold vac was better and how it "supposedly" burns richer, cooler and more efficiently at idle and at cruise. So I decided to try it and yes, it does all of that to my amazement. All are noticeable improvements.... My 75 350 w/a QJet & HEI runs better now than it did set to the OEM specs with ported vac. And since I decided to go with lighter springs in the mechanical advance theres no hesitation nor bog nor stumbling nor pinging even though the static and vac advance is pretty high at idle. One thing one needs to do when going to manifold vac at idle is to also reset the max mechanical advance. Most V8's should be set to a maximum mechanical advance of 36 degrees BTDC with the advance full in (vac disconnected & plugged). All in is generally between 2500-3500 rpm. An adjustable timing light is a neccessity for this tuning. Once set reconnect to manifold vac and let the initial idle timing be whatever it is. It's amazing how well the engine responds to these settings. One thing to note is if the vac advance adds more than 10 degrees to the mechanical advance you need to adjust it down either by adjusting the vac adv module (if capable) adding a limiter (kits available) or getting an advance module that maxes out at 10 degrees. All these will really wake a stock and/or modified engine up. Carry On.

[@grandam]

PORTED= HOT ASS TEMPERATURE IDLING MANIFOLD = COOLER TEMPERATURE IDLING THE END!!!!!!

[@Gkitchens1]

Only fools use words like never or always. Nothing is always true, nothing is never true. There are situations and times in which you use pprted vacuum, there are situations and times to use manifold vacuum.

[@thejunkyardnecromancer]

You are right! I was only being hyperbolic to make a point. If you are running all the old school emissions stuff like EGR, you should use ported vacuum otherwise your vehicle won't run right. Another situation might be if you have a really lobey cam, your manifold vacuum might not be very strong or consistent. It would probably be better to use ported vacuum and a lot of mechanical advance or forego the vacuum advance all together and run a locked out distributor.

[@Gkitchens1]

@thejunkyardnecromancer big cam and boost cars was the first thing that came to mind and the reason I commented lol

[@gearbanger57]

Who tunes a hot rod according to a Chilton's manual? Always used manifold vacuum on a recurved distributor.

[@thejunkyardnecromancer]

This is the way!

[@charleswieand4445]

My grandpas old Diamond Motor dump truck 4 cylinder had a distributor spark advance on right side of steering column with a cable running to distributor.

[@thejunkyardnecromancer]

That sounds like a cool old truck! Must have been from the 20s or 30s to have a manual spark advance like that!

[@MrElusive1]

makes sense. but have you tried to make the other shoe fit? I am all about the smart way. nice job explaining.

[@tnoutlaw73]

you are absolutely right. I was working on a 1972 F600 2 weeks ago. the owner had the V advance on the ported vacuum port. ( after market holley 500 2 barrel) It was not running good at all. I Moved the line to the Manifold port. verified the timing and idle. he says its never ran better.

[@1Coolbanana]

Ive used both and found stock vehicles work great on ported and camed up engines work great on manifold but really depend on each engine, they are all different.

[@rescuedandrestoredgarage]

This was a lot of fun,brother. Great information, and I loved the poke the bear.

[@thejunkyardnecromancer]

Haha. Thanks man!

[@adampinczesgarageandfabric9930]

sorry bud I've been running ported vacuum for more than 10 years. everytime I hook it back to manifold vacuum I lose my power off the launch. My low compression SBC likes ported vacuum advance. It has to be set up correctly to work obviously but if it works on your setup you'll never go back.

[@thejunkyardnecromancer]

I actually was a hardcore ported vacuum guy a while ago, but after reading a really good article by an engineer at GM and testing it out myself, I switched to manifold vacuum.

[@aprilsfoolracing4594]

I'm with You,and for all of them in doubt,let me give You an example: Take one stroked Jeep inline 6 284 c.i. around 300-315 hp ,raise the compression to 10.6, put a rather healthy camshaft in it and park in the middle of the sunshine on a hot summerday ,ignore the fact that the car has a radiator from a 1.8 litre Volvo engine. OK how long will the engine run before it gets boiling hot, wel without any vacuum or with ported vacuum it took 5-7 minutes after reaching operation temperature before it boiled, when I connected to manifold vacuum I could leave it running for 15-20 minutes without being so hot that it boiled. To low ignition will cause any car to go to hot, with manifold vacuum it got enough ignition advance to live to tell the story...

[@JJBaker1405]

Less advance causes more combustion in the exhaust manifold due to an incomplete burn, raising manifold temperature. Advancing timing keeps the burn in the cylinder, increasing cylinder head temp and allowing for a more efficient burn in the cylinder, creating more power (and NOx due to higher temperatures, so not because of emissions)

[@jakewade7388]

You failed to mention that you need to limit/modify the vacuum advance pod if you choose to go this way.

[@thejunkyardnecromancer]

You are right! I'll be going over this in my follow up.

[@johnkennedy2505]

On older engines w/o a/c they would have those solenoids on the throttle but they were called anti Diesel solenoids. To cut the throttle back more after you turned the motor off I had one on my 69 and it was needed. I had one go bad on me and with the idle bumped up to normal w/o the solenoid it would run on all the time until i found a working one in the junkyard. The were not available new in the early 90's

[@jamesboardman7048]

Ive found out it all depends on your engine ,try both see what works best

[@thejunkyardnecromancer]

Indeed! Every engine is a little different.

[@bicylindrico]

I agree with you on this one. Just look at the ignition map of any properly dyno tuned engine similar to your own and it will tell you how to control your advance

[@Bristolcentaurus]

and which map is that on a stock 65 mustang?

[@EduardoAguirre-pj3cr]

Full throttle will generally have less total timing. Because distributor will have to be turned back at idle also. Unless u get the mechanical advance set just right. Been messing around cars for ever and still watching tutorials. It all comes down to camshaft dynamic s

[@redchevy3307]

Here's my $.02, take it or leave it. If your car was designed with manifold vacuum, run manifold. If the engine came with ported, run ported. There's dozens of vacuum advance canisters and they are specific for the engine and the cam and distributor. I've got one that maxed the timing at 7 in. of vacuum, another at 15 in. of vacuum. I currently run one that maxed out at 14 in. vacuum. Also I ran my car at 70 mph, in 5th gear, cruising, guess what, the ported and the manifold vacuum were the same. You stomp the pedal to the floor, and we know the vacuum is the same. There's more to it than switching the tubing between ported and manifold, it's the combo. We've all heard that before. I changed the vacuum source from ported to manifold, it ran worse, sluggish. I suspect if I had a vacuum advance designed for manifold vacuum, or changed the timing, it would have ran fine.

[@Bristolcentaurus]

who says they are wrong? what does the manual for the specific year model of car that is the subject of the service work say?

[@brianhdueck3372]

For driving experience I have in most cases, not all, had quicker throttle response with ported vacuum. I also prefer to fine tune timing with a vacuum gauge after the timing light so maybe it’s just me.

[@thejunkyardnecromancer]

I've never tuned timing with a vacuum gauge, but I've heard similar things about the quicker throttle response from other people. I'm hoping to test this theory in my follow up.

[@Trobertsdsgmach1]

Quicker than what? Theres more to it than switching the rubber hose… carb adjustment, timing adjustment.

[@thejunkyardnecromancer]

@@Trobertsdsgmach1 this is very true! Dan and TH289 claim that running your vacuum advance off of manifold vacuum requires you to close your throttle blades so much that your transfer slots are completely closed off in order to get a proper idle speed. They claim this causes a delay in the transfer circuit of the carburetor, which will in turn cause a delay in throttle response when you stomp it. Their solution is a higher initial timing like 18-22 degrees BTDC, and ported vacuum to control the vacuum advance for part throttle driving. In theory it does make sense, but I think it might not work as well in practice. I'm testing all this right now, and I'll be uploading my findings in another video to come!

[@Trobertsdsgmach1]

@@thejunkyardnecromancer I do not have any distributors with vac advance, all billet msd with light springs and custom weights (rather then full lock out) for street use. All trucks and cars in my garage have full mechanical advance and a curve designed to make the most “power” not the best “power and mileage “. Vac advance has to many things to go wrong in my opinion

[@Trobertsdsgmach1]

Also i do not tune the idle speed with the curb idle screw or any else, advancing and regarding the idle timing is the only way to adjust idle.

[@jamesahr2634]

I agree with thunderhead, bascially at idle its already advance by timing soon as ported vacumm occurs, then your timing is advance as needed by ported.

[@kenrusso9759]

First time watching your channel, your are appositely 100% correct, as someone who actually worked on cars from that time period I can tell you that manifold vacuum is the correct answer. Simple put; Manifold helps at idle and slight throttle when it starts to drop off the engine speed is picking up at the same time the mechanical advance is starting in. I worked at a speed shop and I can tell you many of hot hotrodders would bring there cars in to our place because they were unsatisfied with other performance shops. We would always set the owners straight. .......keep up the good work.....

[@thejunkyardnecromancer]

Thanks!

[@gregstahlman1680]

I have worked on and owned a LOT of pre 68 vehicles and worked at a dealership and NEVER saw one vehicle from the factory using MV. I am still waiting for someone to show all the factory service manuals and vacuum diagrams that show it connected to MV. Been crickets on that for years now!

[@jamesthomas4693]

The way i understand it is the vacuum advance was only supposed to be engaged during higher rpms to equal out the timing because the intervals are shorter between combustion. If I'm understanding your logic here is vacuum advance actuated = good always.

[@thejunkyardnecromancer]

@@jamesthomas4693 The more your throttle is open, the less vacuum you get. This means regardless of which source you connect your vacuum advance canister to, it will only advance your timing the more you close your throttle. It's completely independent of engine rpm. The mechanical advance in your distributor advances your timing based on engine rpm. The only difference between ported and manifold vacuum signals are at idle. Manifold will give you full advance at idle and ported will give you no advance at idle. The debate here is if you want timing advance at idle.

[@craigwall5356]

Your explanation you gave was thorough and well laid out. The one thing I have found is that the most consistent manifold vacuum signature is created at the base of the carb on the primary side of the carb. Your vacuum is more consistent and progressive there than if you pull it from behind the carb on ford's (typically) and in front of the carb on chevy/Mopar. Again were talking "classic " engines, not new gen's. If you were to use a digital Guage so that you could attach a data logger you would see there is less of a vacuum "lag" and it would provide a much more consistent rate of vacuum sweep at the carb base, primary side.

[@thejunkyardnecromancer]

That is very interesting. It would be an interesting experiment to track the signal from the two different sides to see the difference.

[@stuckinmygarage6220]

Thunderhead289 agrees with you. His Carb Cheater (Very Cool) instructions recommend similar idea.

[@billygullifa3245]

The ultimate vacuum advance video by Andy part 1 and 2

[@thejunkyardnecromancer]

Great videos

[@sebkhailer7374]

Weird thing is, my engine is completely opposite to what you're explaining. I used to have my advance on the manifold vacuum and i had all kinds of problems. Power would drop at full throttle and the engine would bog down, bucking at low speeds, hesitation and wantinv to stall on takeoff, erratic and almost untuneable idle. I swapped it to ported without changing anything and virtually every issue went away, better power especially T.W.O., smoother shifting and takeoff, little to no bucking or hesitation, my engine runs slightly cooler and the idle is perfect. I dont even have any emmissions bullcrap on my car.

[@thejunkyardnecromancer]

Did you check your initial timing timing and mechanical advance? You can tune an engine to run on either ported or mailed vacuum. In my opinion, manifold vacuum has the most benefits. My plan is to test this theory in my follow up video on the topic.

[@sebkhailer7374]

@@thejunkyardnecromancer Yeah, we tried to optimize the initial timing and the mechanical the best we could to the manifold vacuum but no matter what we couldn't get it to work right, always had problems.

[@junkyyarddawg]

I tuned my engine to run on manifold vacuum because I didn't know any better. It ran awesome and used different mechanical timing springs etc and had an adjustable vacuum canister diaphragm on a ACCEL blueprint series distributor. I made sure to check total timing too. I now run off ported because I heard I've been doing it wrong the whole time. I have not tuned my engine to run off ported vacuum and I have some pretty bad dead spots and bogging at full throttle. So I believe I can tune my engine to run off ported as well.

[@sebkhailer7374]

@@junkyyarddawg Hell, try it. I'm still new to this timing stuff so i cant tell you right from wrong, only what works for me and what doesn't. I likely don't have a setup like yours and that may be why neither me nor my grandfather could tune my engine to run off manifold vacuum. We were only able to get it to run halfway decent on manifold before switching it to ported without changing anything else, it feels better than a brand new car.

[@junkyyarddawg]

@@sebkhailer7374 yeah I'm currently running off ported on my new Demon. I just haven't tuned it or changed jets etc to see what the problem is. I just used a vacuum gauge etc and adjusted the air fuel mixture. Might be it's lean or too much fuel when the secondaries open up. Not sure but I need to put in a little time to find out. I haven't checked timing either.

[@russellapplegate5661]

Ive tried both ways. I use ported because i dont want to idle at 25 degrees. My engine likes to idle at 13 degrees

[@C10chevy85]

My SBC 350 does as well. No right or wrong port. Depends on where your engine likes it best.

[@donsmanufactory]

Really good explanation from a single perspective. The REAL truth is how you run your advance is dependent on the engine build. The only answer is, give the engine what it needs. Manifold vacuum works great for stock OEM engines most times. Depends on how much advance it is set for. Too much will make it idle bad. If a “bigger than stock” cam is installed manifold vacuum will be lower and fluctuate. If running an automatic transmission dropping it into gear will drop the vacuum and back off timing which will lower the idle which will lower the vacuum more reducing idle speed more and the motor dies. Not good.

[@anthonyparlin9418]

This is the best explanation I’ve heard to date. Makes the most sense.

[@thejunkyardnecromancer]

Thanks!

[@wittysgarage]

Even if it's wrong! 🤣😂 Nice explanation. Looking forward to learning more about vacuums on engines in the future.

[@thejunkyardnecromancer]

Thanks for watching!

[@robertellison4691]

Why did the Chryslers and Fords from the 1960's and 1970's come from the factory with the distributor connected to ported vacuum if it is incorrect?

[@thejunkyardnecromancer]

@@robertellison4691 the theory is the switch was to help meet new emissions standards, but after some more in depth research, I might be wrong on that point.

[@billythebake]

You are correct, ported vacuum advance was designed to meet emissions requirements, and vacuum advance addresses the fact that the lower the cylinder pressure is, the earlier you tend to want to ignite that spark plug UTG and Thunderhead 289 are also (almost) correct - the carbs will often work better with ported vacuum IN A VERY MILD ENGINE Here's the rub: where is the idle transfer slot below your Venturi? Where does your idle circuit roll off (affected by the position of the transfer slot, how open the throttle blades are at cruise), and where does the primary booster start getting enough signal to start drawing fuel (affected by the design of the booster itself, the air bleed, and the emulsion tube)? Some carburetors can tend to have a little lean spot in the transition between part throttle cruise (where the engine is running off that transfer slot) and when the main circuit actuates A vacuum advance pulling off of direct manifold vacuum is beginning to lose a little bit of advance here, but this is the point where ported spark advance will still be coming on strong Masking the feeling of that slight lean area The real fix, as I see it, is to do something about that lean spot Not crutch it with ported spark advance

[@colonelbirko9205]

when you run non std camshaft your idle is more consistent via ported vac , manifold vac will range up and down and quit .... give it a go and see.

[@rorydottin7143]

You got it spot on son.. best economy at part throttle cruising . Thumbs up.. listen to David Vizard and Andy Wood on this subject.. Heads Up!

[@hiswordheals9710]

The one statement we all onow followed by a logical question should put an end to this debate but rest assured it won't. The statement we all onow is WHEN SETTING YOUR TIMING MAKE SURE YOUR VACUUM ADVANCE IS UNHOOKED The logical question would be--- ported vacuum doesnt add any vacuum advance so WHY is the statement of make sure your vacuum advance is disconnected when setting your timing? Why should you make sure your vacuum advance is unhooked---- unless vacuum advance was originally intended to be hooked to direct manifold vacuum? Should be simple enough but I'm sure it will still be wildly debated......

[@livewire2759]

Good video... you make a lot of good points. There are some holes in your research though. (BTW, I'm not just a backyard tinkerer/shadetree mechanic, I went to trade school and got a degree in automotive technology and I've been employed as a mechanic for over 20 years now, so while I might seem like a "know-it-all", I actually do know what I'm talking about and there is no condescension intended). As I'm sure you're aware, testing those two vacuum ports with no load on the engine doesn't really tell the whole story of how the vacuum changes when the vehicle is actually being driven. The only difference between ported vac and man vac... under load... is that ported vac has 0 in. at idle and man vac has full vacuum at idle. Once you crack the throttle open far enough to uncover the ported vacuum port, it follows exactly the same curve as manifold vacuum, depleting as throttle is increased. Therefore, they will perform exactly the same from off idle to WOT.... again while under a load. The only really problem then is the mixture at idle, which can be adjusted rich enough to run cool simply by adjusting the idle mixture screws, with no hot idle solenoid necessary (they actually weren't very common, only a few cars used them). Engineers also compensated for the "sudden bump in advance" when ported vac suddenly kicks in by adding a restriction orifice into the vacuum advance pots on those distributors to smooth the timing curve and avoid detonation and the potential for engine damage. So, while you're absolutely right about how every engine theoretically should run best on manifold vacuum, and you're absolutely right about man vac being used on every engine prior to the emissions era, most stock engines from the emissions era with their original factory equipment will run best on ported vacuum, which actually does provide better off idle performance than man vac. As for some anecdotal evidence... I collect late '70s Chevy trucks, I keep them very much factory stock except that I remove most of the emissions equipment from the ones that came with it and I convert them to manual chokes/manual throttles, and they all run best on ported vacuum, with the original Q-Jet carbs and HEI distributors. They don't run hot at idle, not even my air conditioned suburban with a small block 400 and a stock 195 degree t-stat at 115 F in the middle the summer, and I get 15 to 20 mpg on the highway with them... as long as I keep them under 65 mph, since they have the aerodynamics of a brick (LOL). I've never had any luck running any of them on manifold vacuum, even after attempting to tune them to work with it. I also have a '66 chevy pickup (technically 2 of them, my son has one too) with period correct parts (carb with only a manifold vacuum port and breaker point ignition) and it runs just fine on manifold vacuum, because that's how it was engineered. I've worked on many cars and trucks from the carbureted emissions era and I always run the vac advance on whichever port the books say to run them on, then I tune them to run as good as possible. Older cars that use manifold vacuum run the best when you set the base timing to where the engine has the highest manifold vacuum, and the emissions era cars run best on ported vacuum with base timing set at or a few degrees more advanced from where the book says to put it. That's been my experience anyway...

[@thejunkyardnecromancer]

This is all very true! As for the lean/rich explanation, I should have described that as more dense vs less dense. My description as lean vs rich has caused a lot of confusion, and I've realized it was an incorrect way of describing it. I'm testing all these configurations right now for a follow up. It will be interesting to see as my 68 f250 (with an engine from 1975) definitely would fall into that "ported from the factory" group. I also plan on doing a demonstration with two vacuum gauges (one on ported, the other on manifold) while driving to show exactly what you said. They are exactly the same off idle. Do you have any suggestions of things to test or things to monitor while in testing to get the most complete answer I can? Thanks for your comment and your wisdom. PS - Those late 70s square body Chevys are great trucks!

[@livewire2759]

@@thejunkyardnecromancerYeah, I can see how some people would misunderstand the whole rich/lean - dense/less dense ideas, so you're right, it might be a good idea to clarify that in the follow up video. As for actual experimentation, the only thing I can suggest is to compare the vacuum can on the distributor to a pre-emissions model, as well as the carburetor if you can find a similar one. I'm not very familiar with Fords, but I know some Chryslers from that era used an odd way of supplying vacuum to the distributor. They had an orifice built into the throttle body of the carburetor (thermoquads, perhaps others) that actually connected manifold vacuum to the ported vacuum port that fed the vac advance. I don't really know why they did that, perhaps they were trying to get the best of both worlds... but it would be very interesting to see how Ford plumbed their carburetors or if they tinkered with the vacuum pot on the dist.

[@80sfordguy]

Junkyard the use of ported vacuum is unnecessary for anything more than 200-300HP or if a more than slightly rough idle cam is used. If the classic I6/V8 is bone stock ported vacuum is used only if a ported vacuum switch is used. The ported vacuum switch when connected properly only uses ported vacuum when the engine is cold. The use of ported vacuum port on the carb and a ported vacuum switch is the “old school” version of open & closed loop operation! Once the engine reaches roughly 125F-140F the ported vacuum switch switches the vacuum source from ported to manifold vacuum. This allows the engine to run with less timing at idle to so the engine doesn’t go too lean. Making an engine run lean also makes it run hot in traffic which also increases emissions at idle. Hence ported vacuum is an emission restriction and engine overheat solution when in traffic.

[@larryfeasel2403]

Just because they have followers, doesnt mean they know what they're talking about. You are 100% correct !

[@thejunkyardnecromancer]

Thanks!

[@terrypetty9822]

NEVER connect to manifold vacuum. UNLESS you like gas smell at idle. But it makes only a MINISCULE difference. Any time you are not idling, you are getting the same same same.

[@thejunkyardnecromancer]

@@terrypetty9822 yep. Only difference is at idle!

[@terrygrover6440]

First of all good video, well done, as far as Dan goes he tells people about performance when meanwhile he has the slowest car on KZbin, he doesn't have a clue in my opinion, uncle Tony same deal he talks a good game swapping pistons around to go 13s naturally aspirated, they are always giving misinformation, so thanks for your good information

[@thejunkyardnecromancer]

Thanks! However, both Dan and Tony do know a lot, and do give good advice quite often! They just happen to be wrong about this one thing.

[@joncarroll9613]

I've run both ways. My truck had no emissions on it. Manifold vacuum to the vacuum advance= sluggish acceleration from stop or cruise. Ported vacuum to the vacuum advance= much noticably better acceleration from stop and cruise. If it was hooked up according to manual at the time a temperature control switch was in the manifold. The vacuum was run to manifold vacuum when cold. As the engine warmed, the vacuum was switched to ported. I'm not an expert. I just know how seat of the pants felt. Ported vacuum was better. Sorry for being so long.

[@yeboscrebo4451]

The job of the vacuum advance canister is not to give you timing when you hit the throttle like it does on ported. That’s the job of the mechanical advance. When the vacuum canister is allowed to do it’s distinct job (more timing at idle/low load), you have to adjust the mechanical timing to come in fast and strong like it’s supposed to for good acceleration.

[@stevewheat9030]

David Vizard says manifold vacuum... with his many years of experience in and with engines and the hours he's spent on the dyno....I will go with DV on this one.

[@thejunkyardnecromancer]

Yes! I agree! He is an absolute legend in my book.

[@mechanknuckle]

The ONLY real answer is-- It depends or your particular setup. Some cars, especially hot rods with big cams want ported vacuum. Stock build classics want manifold vacuum. MOST of the time. Again... it depends on your build and your timing curve. Thank you, and Good Night!

[@trailerparkcryptoking5213]

You don’t know how the system works! Buy the book PERFORMANCE IGNITIONS written by Dr Christopher Jacobs and get up to speed! Quit spewing BS! Dr Christopher Jacobs was the premiere ignition expert and consulted to many NHRA and NASCAR teams and built his own ignition company that MSD bought out because they couldn’t compete with him. That’s after he made his fortune developing electronic devices for the medical community and making millions on his patents..... You, uncle tony and thunderhead289 don’t have his credentials....

[@paultice610]

I have a 327 sbc I use manifold vacuum because it idle better and starts easier when cold and better throttle response I am running 11 to 1 compression and 480 lift cam it’s a blast in my Square body

[@honestpeytonsspeedshop]

The only thing you were missing was a white coat and glasses

[@thejunkyardnecromancer]

You're right! I need to get a costume like that for these sort of videos. XD

[@honestpeytonsspeedshop]

@@thejunkyardnecromancer no doubt. Go the whole 9 yards

[@terryzeissler4199]

Perhaps you should consider that the idle speed increases with a manifold vac source is that what you have done is increase the base timing at idle which also increases idle and better coolant circulation possibly resulting in a cooler engine? I don't completly agree with the article but still maintain that the thousands of cars I have worked on in my long carear have had better drivability, fuel economy and lower emissions than any of the ones that came into the shop with the distributor connected to the manifold. How do I know this? That's because every car I tuned was done with a before and after full diagnostic on my engine analyser with infrared gas analyser. As I was taught by my mentor half a century ago : Test, Verify, Repair, Retest. Test to find the problem, do not guess. Verify you have found the problem by coming at it from a different angle. Repair the problem you have identified. Retest to make sure the problem is fixed before you give it back to the customer. This results in almost zero comebacks and the customer not paying for unneeded parts, The two reasons that the public does not trust the automotive trade. And by the way I agree with Uncle Tony on this, his reasoning is very sound.

[@thejunkyardnecromancer]

That is a good way to go about it for sure. That's my mentality going into the testing for my follow up video. Unfortunately, I don't have access to an infrared gas analyzer or anything to test emissions. Do you have any tips or alternative methods I could use during my testing? I want to do this as objectively and as scientifically as possible. Gathering the most data as possible in the process.

[@3rdpig]

Good explanation, and absolutely correct. I heard UT say "always ported" and was scratching my head since most of his vehicles are pre emissions. So many band-aids were invented and applied during emission/carb era and most of them, while improving tailpipe emissions, were counter productive to power, drivability and engine life.

[@thejunkyardnecromancer]

Thanks!

[@petesmith5092]

Power IS economy!! Hot rodders have been arguing this for decades. But the fact is, squeezing the most bang out of each and every droplett of fuel is what economy and power both are all about. And FINALLY, our government has seen the light in that regard. But what did we get for all of our efforts except for higher prices of everything. Bureaucratic fat-cat pocket lining programs, fills me with an urge to defecate.

[@thejunkyardnecromancer]

@@petesmith5092 you are right! Power is economy!!! That should be put on a shirt!

[@petesmith5092]

@@thejunkyardnecromancer you are welcome to use that. Just cut me in for 5%....🤣🍺🍺

[@jeremyking5684]

Always ported on street engine, not going to make difference except with manifold vacuum idle will be higher ,and you will be idling it down closing more of your transition slots. Vacuum advance is designed when you accelerate vacuum comes on advancing timing giving more power and better fuel mileage.

[@thejunkyardnecromancer]

Vacuum advance is for part throttle situations only.

[@James-pz8rm]

You are dead on!! I'm in my 60's and have been working on cars with my family since I can remember and I was a licensed mechanic. Anyway I remember all the cars having manifold vacuum until the 70's when they went to Ported for emissions reasons as you said. One of the common problems in that era was a poor idle or stalling because the diaphram in the vacuum advance would rip so the vacuum advance did not work and also would be sucking air. It is sooo nice to see someone correctly describe the use of vacuum advance. GREAT JOB.

[@thejunkyardnecromancer]

Thanks!

[@gregstahlman1680]

I don't know where you worked as a mechanic, but I NEVER saw a factory car prior to 68 that used MV. I would love to see the service manual that shows connection to MV direct to the dist.

[@tonylinkkila7617]

I'm a retired master tech and have almost always connected a vacuum advance to Manifold also. The signal to the carb is better , aiding in tuning, and the timing retards under load resulting in more power and less chance of detonation. This allows more base timing adjustability due to the specific engine built specs.....This has worked for 40 years for me.....Just my 2 cents.....Have a great day!!!

[@johnny0454]

You are exactly right, so many people get this wrong. The vacuum advance is there to give you more timing at idle (enabling less initial for easier starting) and while cruising (for efficiency and emissions) and then FALL OFF during full throttle (where pre-ignition, saprk-knock, detonation, whatever you want to call it, is a concern and timing must be dialed BACK from its part throttle, cruising setting.) Not the other way around..... it should not be giving you any additional timing during WOT, that is what the mechanical advance is for.

[@thejunkyardnecromancer]

Exactly!

[@MVPisME383]

I tried both my car runs way better on ported, i tried manifold first then realized vacuum is highest at idle so when i punched the gas it was pulling timing out so the vacuum and machanical advance just cancelled each other out, never did run right, when i swapped to ported and readjusted "advanced" initial timing to make up for the swap she runs like a rapped ape

[@newguysgarage6802]

Here I was thinking I might have some actual competition with this video battle 😂 You made it way way too easy to prove you wrong bud 😏

[@thejunkyardnecromancer]

Good luck!

[@jeremybodell3619]

I’m with you on this one. I’ve had many a conversation at the cruise night that started with “you got your vacuum advance hooked up wrong”. It’s been my experience that manifold vacuum is especially best with low compression engines they really like the extra timing at idle.

[@thejunkyardnecromancer]

Definitely!

[@KC9UDX]

I don't think compression is what matters. I have high compression motors that work better with manifold vacuum advance. It might have more to do with cam timing 🤷‍♂️

[@jeremybodell3619]

@@KC9UDX yeah a high commission engine with a big cam probably would work well that way. An engine with 10:1 and a mild factory cam doesn’t tend to respond the same to the timing at idle. Pretty sure it’s the cylinder pressure that’s the factor.

[@MarcBchannel]

Yup! Or if you have a lumpy cam. More timing=happy idle👍

[@mickangio16]

​@@MarcBchannel Until you drop your automatic trans in gear and lose that manifold vacuum.

[@double01red54]

I’m not sure why so few people don’t make this connection-if you have a choppy cam that doesn’t pull any vacuum, use manifold to bring your cylinder pressure back at idle, and close your throttle blades enough to have your idle mix screws make a difference. For a smooth idling stock set up, use ported for mileage.

[@Dancing_Alone_wRentals]

Most interesting. i hope loads of people get to see this.

[@thejunkyardnecromancer]

Thank you! I hope so too!

[@PaulCTownsend]

Stock vehicle ported, little bit of a lumpy cam manifold. Manifold vacuum on a lumpier cam if you want to get more vacuum to your brake booster. Also on manifold vacuum sometimes your engine will tend to diesel a little bit when you shut it off.

[@thejunkyardnecromancer]

@@PaulCTownsend good to know!

[@kencornwell]

When I worked as a mechanic in the early 80's I had the vacume on the manifold and I remember that becasue when adjusting the the carburator with a vacuum gauge I had vacuum and was looking for the most I could get at idle. So maybe you are right. I do like the fact that on the port on the carburator you don't get advance untill you hit the throttle. The argument continues.

[@ericdolby1622]

Good luck tuning a big cam using ported vacuum.

[@8.2deck]

One very important thing I think you may consider is deceleration. Deceleration (at least in my experience with a manual transmission) is usually much richer than idle, light throttle, or wide open. I spend a lot of my time decelerating down winding roads than I ever do idling. So having super high vacuum and possibly at times fast piston speed with a rich mixture may not be ideal, but that's also under low cylinder pressure so maybe it doesn't matter. Compression ratio is a important factor. Piston speed is another. If set base timing at 14 degrees then add all of my vacuum advance is that too much timing for my piston speed? In my experience yes, so then i adjust my vacuum advance ratio down which could hurt part throttle performance. I think it's very important to try both of them out yourself and for each car.

[@thejunkyardnecromancer]

This is something I didn't consider. I'm going to have to research this.

[@petesmith5092]

​@@thejunkyardnecromancerSir, i commend you, and offer congratulation of your mind being open. And your willingness to do your homework cannot be left out!

[@reevesautomotivefarm9614]

Sorry but that is wrong. my Nova, 327, idles just fine at 28 degrees with the manifold vacuum. Also cranks much better than when i didn't no better and was running ported.

[@stevenbelue5496]

@@reevesautomotivefarm9614 so you have vacuum when your cranking

[@chevy6794]

Wouldn’t you want less advance at idle for smoothness and better starts?

[@thejunkyardnecromancer]

Not in my experience, but I plan to put this to the test in my follow up video!

[@chevy6794]

@@thejunkyardnecromancer My old 327 would not even hot start with too much initial. Some guys running hot street engines need to crank em and then turn on the ignition once there rolling. Saves starters. I find advance gives you a choppier idle. I guess that a preference thing but I personally like street manors. Especially when your fairly tame sounding car pulls on the one that barely idles.

[@thejunkyardnecromancer]

@@chevy6794 interesting. Did it have an aggressive cam? My truck and my mustang both start and idle easily in hot and cold conditions with the vacuum advance connected to manifold vacuum. Both are inline 6 engines in mostly stock configurations.

[@chevy6794]

@@thejunkyardnecromancer ya. It had a bit of a cam. Nothing too crazy. Hydraulic flat tappet. High 9s maybe 10:1 compression. Camel back heads. Headers.

[@janamo70]

Even David Vizard says: use manifold vacuum. I'l take his advice.

[@jimmywilson1388]

Geez Louise, I thought I finally knew which one it’s supposed to be connected to but now idk again…😂 I’m about to just block the vacuum ports off and say the hell with it…😄

[@thejunkyardnecromancer]

Do some testing! Run both and find out for yourself which is best! Could be fun haha.

[@jimmywilson1388]

@@thejunkyardnecromancer I was just clowning… It makes sense what you said. I’m just a fuel injection guy so I’ve never really had to deal with that until I got that old 72 Ford Ranger… I’ll probably go with fuel injection eventually in that truck. You would think old guys that have been dealing with carburetors their whole lives would have really tried to figure that out by now…🧐 Idk, thanks for the info…

[@thejunkyardnecromancer]

@@jimmywilson1388 fuel injection is definitely better. What engine is in your truck?

[@jimmywilson1388]

@@thejunkyardnecromancer It’s a 302 and 3 speed transmission. But they put that stupid floor shifter in it…🤦🏻 They should’ve got the good one at least. I think it’s got the Mr. Gasket brand. They don’t even make them anymore. I would’ve went with the Hurst shifter. But anyway I think I’m gonna go to pull a part and try to find an explorer engine with the GT40p heads.I might just try to find a world class T5 for now and then get a Tremec later. I was kinda thinking about building a 347 stroker and get some better heads. Maybe some performer RPM’s or the twisted wedge heads. I just got it about a month ago so I’m just tossing ideas around right now…😄 It’ll be quick when I get done with it though and still be drivable…

[@thejunkyardnecromancer]

@@jimmywilson1388 that sounds like a sweet project!

[@keithwiebe1787]

The problem with hooking to manifold is on downhill runs when the throttle is closed. The advance can be so far advanced that the engine misses going downhill.

[@thejunkyardnecromancer]

I'll take note of this and add it to things in testing for my follow up! Thanks!

[@truthboomertruthbomber5125]

How can the engine miss on closed throttle? There’s no load on the engine. Lean popping is not missing. Being lean on overrun is beneficial.

[@DaRkmatter5.8]

There is really no factory setting.. it’s trial and error give the motor what it want some time have to try both see what works for the motor set up .. messing with ported or manifold vacuum for timing changes a lot .. like I was told I ask the same question to my engine builder some time he would give get up set with say it point blank try both the motor will tell you if it likes or don’t like it… I have even hooked the distributors vacuum to manifold see what would happen the motor rev up on it’s own.. my diss is set up with different springs wow did I have days of messing with them springs see how the motor acted

[@TheGT350Garage]

Good video. If you think about engine operation from the more modern approach where the harder the engine is working the greater the load the engine is operating at, you can draw a correlation between the timing values used in electronic fuel injection engines and on engines with dual advance distributors on manifold vs ported vacuum. This is a point I’ve covered previously in my own videos, and it’s very explainable that way. Simply put, ported is wrong for most engines, it over advanced the engine and can lead to internal damage. I had a customer with a 1937 Chevy street rod running a 383 bring his car to me for a dyno tune years ago, I made significant adjustments to the carburetor and distributor including putting the car on manifold vacuum for the distributor advance. The car picked up over 50hp from the tune, ran 25-30°F cooler, and had drastically improved drivability. Before the customer drove it, he scolded me about connecting the advance to the wrong vacuum source. He wanted to change it, I insisted he drive it first. A couple miles in, happy with the improvements in power, he remained hell bent to show me the error I had made, he stops, jumps out, moves the hose and hops back in proclaiming “you’ll see!” It ran terribly, pinging away from a stop. I’m happy to join you in confirming manifold vacuum is correct side of this discussion.

[@thejunkyardnecromancer]

Thanks! And excellent story!

[@rong4189]

Well, the way I was taught to check timing was Step #1, ‘Disconnect vacuum advance’ so that meant manifold vacuum and the fact that the weak idle mixture NEEDS more advance than the mechanical initial timing.

[@livewire2759]

You're absolutely correct... watching on a scan tool how modern engines change their timing can give us a good idea how to tune older engines, and they do all run higher advance at idle, indicating that analog distributors should run on manifold vacuum... HOWEVER... you have to keep in mind that most (if not all) vehicles from the late '60s to the early '80s were DESIGNED to run on ported vacuum operated vacuum advance, so they'll run better that way if they're still in stock configuration. I have no doubt that the hot rod you mentioned ran better on man vac, but that's because you were able to tune it to run best that way. Yes, stock engines can be tuned to run better on man vac as well, but if they haven't been professionally tuned, they should be run on ported vac the way they were intended, to get the best drivability out of them.

[@TheGT350Garage]

@@livewire2759you clearly aren’t grasping that “ported” vacuum was a shitty attempt to reduce emissions and had no performance or efficiency benefits whatsoever. Just look at what the manufacturers did to neuter engines in the early 70s in the name of “clean air”, ported vacuum was a key player in that BS. It was all trial and error, because they had no way of simulating combustion and no real understanding of how to produce reasonable power and lower emissions with mechanical/analog fuel control. Take a look at a stock 1985 Mustang GT 5.0L HO 5-speed some time. The distributor was connected to a thermal vacuum switch that used ported vacuum warm and manifold vacuum cold. The problem with ported cold was the engine didn’t have enough advance for the lean mixture when there was no heat in the engine to aid fuel in becoming a vapor. As soon as the engine warmed up, the engineers killed off the vacuum advance to slow the idle speed and limit emissions. Manifold vacuum produced higher CO and HC numbers at the slower idle speeds that were not compatible with catalysts. But that it in a nutshell, ported is an emissions technology, and offers no realized performance advantages. It can and does however provide timing later than needed and can put the engine into knock if you aren’t running EGR or your carburetor is not calibrated properly. It is also not compatible with higher compression combinations using larger cams which is why so many people simply switch to a mechanical advance only system, attempting to run ported advance doesn’t work on the more aggressive combinations, however, manifold vacuum does when applied correctly and can be a huge benefit to idle stability and operating temperature.

[@livewire2759]

@@TheGT350Garage "You clearly aren’t grasping that “ported” vacuum was a shitty attempt to reduce emissions..." Ok, if you want to be that way, I can be a jerk as well... You "clearly aren't grasping" why vacuum advance was invented in the first place. You clearly aren't grasping that it's not a power adder or performance device. You clearly aren't aware that it's sole intention was to RETARD timing under part throttle to heavy throttle acceleration in order to help reduce or eliminate knocking. You don't seem to understand that they retarded the base timing on those engines to make up for the advance caused by using manifold vacuum at idle. You also don't seem to be aware that the reason why they used manifold vacuum for this up through the mid '60s is simply because nobody had come up with the concept of "ported" vacuum yet... they didn't need to because manifold vacuum worked "well enough". That doesn't mean that has always been ideal. Yes, the concept of ported vacuum came from attempts to reduce emissions at idle, and it works to do exactly that... when the engine is warm. You seem to be ignoring the fact that man vac/port vac makes no difference when a carbureted engine is cold because they run on a fast idle when they're cold... that's right, while warming up the throttle is open to the ported vacuum port which, if connected, sends vacuum (the exact same amount of vacuum that a manifold port would send) to the vacuum advance, advancing the timing at "idle" during the warm up cycle. Again, if you watch data on a scan tool, you'll see that modern engines do this same basic thing... increasing idle speed and advancing timing until the engine is warm. Now, most of all, what you don't seem to be grasping, is that when car makers started using ported vacuum to run the vacuum advance, they also re-tuned and re-engineered some things. These things included using different weights and springs to tune the mechanical advance to work better with the ported vacuum advance, as well as changing the vacuum pots themselves to work better with ported vacuum. Not only did they start recommending more advance for base timing to make up for the lack of vacuum advance at idle when using ported vacuum, most manufacturers used some sort of restricting orifice in the vacuum advance system to optimise it for use with ported vacuum to eliminate the problems with suddenly going from no advance at idle to near full advance at off-idle. When they did this, they found a happy surprise that they could actually get better throttle response from closed throttle to off-idle than the old manifold vacuum operated systems did. This is why, when you just switch one of these emissions era engines from ported vacuum to manifold without making any other changes, they tend to stumble or have a "flat spot" just off idle. Yes, you can tune that out, but if those orifices are still there, you still won't get ideal performance without changing parts. This is also why those mustangs you mentioned used a system of switching between manifold vacuum and ported vacuum. Chrysler used a similar idea in their thermoquad carbs where they connected ported vacuum and manifold vacuum together inside the carburetor with a very small orifice between the two... essentially using both to operate the vacuum advance. "It is also not compatible with higher compression combinations using larger cams..." That's an interesting point. The only difference between ported vacuum and manifold vacuum is at idle where man vac will be full vacuum and ported vac will be near 0. Just off idle, the ported vacuum port is uncovered and at that point it will always be exactly the same as manifold vacuum. If you don't believe me, get two vacuum gauges, hook one to man, the other to port, with long enough hoses to be able to read them from the driver's seat, then drive the car and see what they do. Under load (which wasn't demonstrated in this video) they equalize at off-idle and drop off at the exact same rate while opening the throttle. So, considering that big cams with lots of overlap naturally run low manifold vacuum at idle, how could running manifold vacuum be any different than just running ported vacuum with the base timing increased? Sure, manifold vacuum may be the best choice in high performance applications where drivability isn't much of a concern, but for cruisers and daily drivers, you'll find that using ported vacuum with a proper corresponding tune will provide better drivability performance. In conclusion, I'm not saying that you should NEVER use manifold vacuum, and I'm not saying that you should ALWAYS use ported vacuum. I'm saying that it depends on what engine you have, what parts you have, and how you're going to be driving the car. Using blanket statements like "never" and "always" is a dead giveaway that a person probably isn't as much of an "expert" as they think they are.

[@williamcharles9480]

There's an article on-line by Lars Grimsrud, an aerospace engineer and muscle car collector and restorer under the subject of "vacuum advance". It's a pretty thorough 4 page PDF that mentions the benefits of using manifold vacuum. Pretty interesting stuff. Google: Lars Grimsrud, Vacuum Advance the article should pop-up.

[@thejunkyardnecromancer]

Will do! Thanks for the info!

[@markcole6475]

On any performance oriented build I rarely hook up the vacuum advance! Unless it’s a low budget build where I need to manipulate timing in a cheap manner! Like if a stock starter won’t crank over a hot engine with desired initial timing ….(stock starters on older engines are junk) Ever try to start a hot Chevy engine with a stock starter with advanced initial timing with a bigger cam? 😅

[@kenalex0353]

Early emission systems ran both the EGR and vacuum advance off of ported vacuum after warm up. To marginally compensate for the reduced output of these low compression emission choked engines they could run slightly more initial advance and have more aggressive centrifugal advance since the EGR cooled the charge and reduced detonation. I believe ported vacuum was used to coordinate the application of EGR and vacuum advance to mask drivability issues at light throttle and reduce detonation at throttle tip in. Of course once engines of this vintage started wearing (30k miles or so) the EGR could be disconnected, the advance moved to manifold vacuum to significantly improve drivability for the next 30k miles until the carb started malfunctioning, the air pump seized or oil became part of the combustion mixture...

[@thejunkyardnecromancer]

Yes! Exactly! Haha

[@thejunkyardnecromancer]

@@michaelgreer8659 there are some advance canisters that retreats timing. Ford used them for awhile. They had two vacuum nipples. But most normal vacuum canisters advance timing BTDC under a load.

[@darrylsm]

Not agreeing or disagreeing , but the egr open at idle kills the engine , and runs poorly . I can see the argument for the distributor, but not the egr.

[@christopherwatson283]

? Ported EGR goes through a Thermo-Valve. Manifold for Distributor Advance. I don't think he's referring to Multiple Port Vacuum Advance Distributors/Systems. Look at the Timing Curve Specs. Base Timing, Timing at Idle. Then Timing at Designated Position for the RPM. Ported will have no advance at idle. Not a Good Thing. Thermo-Valve for the EGR. EGR applied when Cold will stall the Engine. Ported to EGR. EGR applied at Idle will stall the Engine.

[@petesmith5092]

​​​ E.G.R. valves have always been electric over vacuum controlled. coolant temperature controlled "ported" vaccum was for the pre-heat tube to air cleaner basket, to prevent venturi icing, but that was early on. Anytime you open the EGR valve to an engine running at any RPM, it makes it shake like a dog shittin' a peach seed, if it don't kill it. Which is why exhaust gas recirculation is controlled with a pulse width modulated solenoid. All EGR is anyway is a fancy way of saying internal vacuum leak!