How To Choose Between Timed or Manifold Vacuum

[@Digitalsharecropper]

This is apparently the only guy on the internet that gets it. There isn't a right and a wrong, you just try both. It's so easy, it's switching a vacuum line! Some cars will like ported, some do better with manifold. Try it one way, then switch the vac line. Takes a minute. Nobody is wrong or right on this, just experiment. No big deal. Thanks for the common sense !!!!

[@427v8]

ported id for emissions, it provides zero performance or other anyother improvement. It only works if your timing curve is jacked up

[@Mikefngarage]

and vacuum and mechanical both work. It just depends. on how you drive....your rpm range. Honestly I use mechanical advance and have changed to vacuum and cant notice any difference.

[@1crazypj]

In the 50+ years I've been 'playing with engines' that's the first time I've seen the 'spiral' of engine events. You had a real smart shop teacher

[@65sohc]

You left out what IMO is the biggest reason for deciding between timed and manifold. With a lumpy long duration cam the engine obviously requires a higher idle speed to keep running. Normally this is done by way of the curb idle screw. However, as you screw it in you run the risk of exposing too much of the idle transfer slot in the carb. The result is a flat spot off idle. By adding manifold vacuum advance, torque is increased, raising the idle speed and allowing you to back out the idle speed screw and reestablish the correct relationship between the throttle blades and the transfer slot.

[@MuscleCarSolutions]

There’s only so much detail that can go into one video. If I went down every rabbit hole, these would be hours long and no one watches that long.

[@stuckinmygarage6220]

I'm glad u said this. I didn't build my engine, but, yr situation is exactly what mine is. I need to study the timing and AFR stuff more, also.

[@DANTHETUBEMAN]

The balance between carb and distributor tuning, the carb has a job to do, even fuel/air through the rpm, I like starting at the transfer slot adjustment, then timing adjustments. I use to chang the idle screw and ran in to problems. I also rev without vac advance to see when my mechanical is coming in.

[@frankglasgow]

@@MuscleCarSolutions im going through your videos again to make sure I'm not missing anything

[@frankglasgow]

@@MuscleCarSolutions i will watch a long video. I'm gen X

[@rogerstephens8019]

At 67 age I'm like a danged kid when I get to playing around with these small-block chevy's with carburetors ! Especially the ole standbye EDELBROCK 600 cfm !HELL! I've made these things do things unheard of by experimentation and playing with timing,vacuum,fuel and such ! Great video brother !!!

[@jackwillson8099]

When I dumped my 3.23 gear in my 455 oldsmobile , and went 4.56 gear 10" converter hot cam , dump the vacuum advanced ran like a beast

[@Bige4u]

I've always used the timed port with my HEI distributor along with a 10degree vacuum can for years before i knew any better. Now im using a progression ignition distributor, its all electronic(no springs/weights), it uses manifold vacuum pluged into its MAP sensor. You can adjust the initial as well as full timing and other parameters on the fly via bluetooth with either a cell phone or tablet from the driver's seat. Good Stuff

[@robertclark7848]

I think you give the best videos on carbs especially edelbrock carbs you helped me fix my carburetor problems I was having I used a tune up kit to get it to run better especially after my heads were upgraded and cam tuning thanks for all of the help, you’r awesome. On this subject ported verses vacuum both will work but it depends on what you’re trying to do I mostly use ported but if I want more responsive throttle vacuum works better but normal driving ported but anyway thanks for the help

[@MuscleCarSolutions]

Thank you. I’m glad you like the videos. As far as which to use, the good news is you have both options open. If you want to try ported and the engine likes it, good deal! If you try it and manifold works better, you’ve found the solution. A carburetor is an analog part. It does have plenty of combinations of features to help tune to a situation that’s best for the application. Try both! See which the engine likes and have the best drivability.

[@kkyler9582]

My 350 crate motor from Jegs prefers ported. I believe it is because my total timing is at 36 degrees which landed my initial timing around 18 degrees. If I plug into manifold vacuum it makes very little difference at idle. The motor is more responsive off the line and overall performance is better when plugged into ported. So try both and go with what your engine likes best.

[@MuscleCarSolutions]

Always the best advice. You have both options. Try them! The engine always tells you what it likes best.

[@johnc7431]

God what a awesome video I have been playing with my 302 for the past couple months I'm on portage vacuum I do have a little bit aggressive cam I've been tuning my carburetor getting good results and playing with my distributor. I'm excited to try manifold vacuum after listening to your demonstration. It is sluggish out of the hole but runs really strong at the high end I just found your channel and now I'm a subscriber keep the videos coming I'm sure I'll learn more from you have a great day

[@MuscleCarSolutions]

Give it a try! Let me know if you have any questions.

[@Dr_Reason]

Timed vacuum predates EPA. Most early Pontiacs used timed vacuum. It tends to give a smoother idle and the power comes in as you tip on and the vacuum advance kicks in. It makes the engine seem eager.

[@TheThirdWheel618]

Funny my son picked up my grandmas 66 Cadillac deville and it had all the smog crap on it EGR, smog pump , canisters etc i was surprised to see that on a 66 although it wasnt mandatory in 66 Cadillac was already using it .

[@Dr_Reason]

@@TheThirdWheel618 I have also seen some of this on California delivers cars, even a 67 Corvair with air pump.

[@gorkzop]

Chrysler started used the timed in the 1920 or 30s. In the time Harley was allowed to lube it's chain with its own oil and all engines spit fumes/crankcasegoo on the road. Who believes this was emissions is delusional 😉

[@TheThirdWheel618]

@@gorkzop I just hope that we have gas within the next couple of years so we could continue the debate

[@SMOBY44]

Actually, simply, vacuum advance is used to advance the timing at part throttle cruising. Part throttle is a lean mixture and that lean mixture requires more time to burn. Ignition timing is done with the vacuum advance disconnected, set total timing then reconnect the vacuum. Vacuum advance has nothing to do with total timing, it's just a way to get more advance at part throttle.

[@MuscleCarSolutions]

Nicely stated and correct. Any vacuum or mechanical advance of the timing is referenced on the load of the engine.

[@wolfbarber9272]

I have a 290 HP 350 motor it runs best with just mechanical timing it gave me a lot of trouble running timed and manifold vacuum plugged both of them off and it runs great.

[@ryanmiskin8925]

same thing on my Corvair with the flat-6 in the rear. With either vacuum hooked up I'm at 48-52* total timing when cruising easy I get way too lean and have random misfires. Plug the VA and I'm at 34* total and it works smooth as butter and my afr readings (have a bluetooth setup for each side since it's dual-carb) stay in that 13-14 area when just easy cruising. If I have the VA hooked up then it'll have spikes at easy cruise and on deceleration, but be fine when I have my foot in it a bit...but too much in it and I'm pinging.

[@Tk-ou9ec]

I found that manifold vacuum works best on my mild 318! Idles better and off idle response is more lively. I’ll stick with it. Every engine responds differently so best to try it for yourself.

[@donphillips7671]

Thank you. Great video! Trying to figure out my newly acquired "57 Chevy Bel-Air with a 350.... its getting better!

[@CashMullen-ng4sr]

Well, if you want your street driven carbureted engine to run cooler and more efficiently (especially with a bigger cam), you use full manifold vacuum. Using manifold vacuum will give you a smoother idle and use less fuel when idling because with the low fuel/air volume in the cylinders with the earlier spark advance makes the engine more efficient. The idle speed will then increase using manifold vacuum and adjusting the idle speed down will reduce the fuel consumption and result in a smoother engine that also generates less heat so it will run cooler when at idle in traffic. My 1979 Pontiac Trans Am 400/4-Speed with a big cam and high CR 1970 heads runs at least 10-15 degrees cooler and gets 2-3 more MPG with the vacuum advance connected to a full manifold source.

[@MuscleCarSolutions]

That’s not a universal solution. What applies to one doesn’t apply to all. There’s so many inconsistencies and inaccuracies here.

[@chirkware]

Thanks, excellent information and easy to follow! I'm trying to get the 351w in my newly acquired 86 F150 4x4 tuned. Someone swapped out the stock 4 barrel for a Holley 4160. When I got it, the plugs said it was running VERY rich, and I finally figured out it was using manifold vacuum. Since I'm going to be mostly street driving, and will be using it as my daily driver (hopefully), I'm more interested in economy vs performance, so this video reinforcing my thinking that timed vacuum (I'm seeing it called ported in the other videos I've watched) is what I want to stick with. I'm now your newest subscriber.

[@MuscleCarSolutions]

Ported is always the best choice on a street driven vehicle. Try it out and keep tuning!

[@pjnelson8971]

That's backwards. You need vacuum advance at idle for the most efficient idle tuning. The only way you can get vacuum advance at idle is with manifold vacuum.

[@seaox2109]

I have a brand new pertronix vacuum advance distributor and the factory weights allow it to advance 24°. When determining total timing, how would I factor in the vacuum advance? If I set it at 10° base timing and mechanically it will advance another 24°, that would make total timing 34°. How do I know how much the vacuum advance is advancing and should I take that into account? I’m planning on using the timed port on the carburetor. Thanks again for another great and informative video!

[@65sohc]

I had a Pertronix on a smallblock Ford. The vacuum advance was around 20 degrees so at cruise total advance as 54 degrees which was far too much as the engine ran very rough. I ended up buying an adjustable vacuum pod. Installation required complete disassembly of the distributor. After one adjustment the internal mechanism inside the pod broke which apparently is very common. Fortunately it broke at a reasonable setting of around 12 degrees. I believe Pertronix dist for GM come with an adjustable pod, but it is just as fragile. As to your question, the best way to determine vacuum advance is to see where your timing is at idle and then apply suction to the pod with a Mightyvac and see how far it advances. On the other hand if your engine doesn't ping and doesn't run rough during cruise you can assume the vacuum advance is OK and not worry about it.

[@tooljunkie6003]

Another great video simple and detailed explanation

[@MuscleCarSolutions]

Glad you liked it!

[@2nd66tube2]

the issue I found with manifold vacuum on my engine is I need to increase the idle but that increased the engine trying to diesel after the ignition was turned off. perhaps If i was to use an idle up solenoid it may have worked better than just turning up the idle screw. 5.0 B303 1406 Edlebrock Performer 5.0 heads DuraSpark II

[@danw8985]

@2nd66tube2 advancing the initial timing will raise your idle allowing you to close your throttle blades more. Eventually the dieseling will go away when you get that set. If you have too much initial your distributor may input too much total timing if on ported vacuum. Change your vacuum source to manifold and readjust your initial to your proper timing that keeps your idle happiest without dieseling. The manifold vacuum will essentially cut out the canister timing at rpm so you can get a proper total timing with raised initial and centrifugal without pinging. During cranking the manifold vacuum is low enough that it will keep your distributor retarded enough to keep starter load to a minimum also and allows easy starting.

[@TheThirdWheel618]

Ii never had that perspective on the time ......and why I need to add a little more time untill I seen your drawing about timing degrees awesome appreciate that ..

[@mattfulton6847]

I have a 4 speed '69 roadrunner w/stock 383 (bored 30 thousandths with oversized rings and hardened valve seats). I have had it 38 years. I installed a 650 thunder series (1806). An old motor head tuned the carb drawing manifold vacuum, not ported. Played around with sluggish acceleration for years (don't drive it much) and this year had fuel pump failure. When I replaced it it ran better than ever. I would like to retune the carb now that it has correct fuel flow. Instead of reinventing the wheel, and as a general rule, what is the best set up for this car (metering rods, jets and springs)? Should I go back to the factory set up and start there? Timing is about 12 degrees at idle and I run Pertonix electronic ignition. Thanks and great videos!

[@tommyboy1two]

I love your technical videos

[@MuscleCarSolutions]

Very much appreciate that!! Thank you!

[@lukefranklin2263]

Love your videos buddy! I normally just use a manifold port on my intake. Makes it more simple to me. Can you give us the steps to set timing the best with the use of vacuum advance while using manifold vacuum?

[@MuscleCarSolutions]

@@lukefranklin2263 one size fits all never fits anyone. The engine will tell you what it wants. Assuming it’s always manifold is never the right solution. Yes I’ll do a video on this.

[@lukefranklin2263]

@@MuscleCarSolutions why do you think my engine runs cooler on manifold vacuum? It’s the biggest thing to me that makes the choice easy.

[@MuscleCarSolutions]

@@lukefranklin2263 if this was universally the case, then why haven’t the carburetor manufacturers eliminated the ported option? The cost savings would be extremely advantageous to their profitability after eliminating the cost of the component and machine time. The reason why is there isn’t only one option for every situation. Sometimes it’s manifold, sometimes it’s ported. Sometimes it’s best to lock out the distributor and not use either!

[@lukefranklin2263]

@@MuscleCarSolutions oh that’s an easy answer of why they make them still. They are controlled by the same people who wanted you to wear a mask in your house lol.

[@kj9219]

Tried both ways on my 283. What made the most difference was the initial timing. Ported or full vac didn't seem to make much difference..

[@samueltorres7555]

Seeing the results with the gauge one can't really argue.... However... the msd manual calls for ported vacum on the vacum advanced. Weird.

[@stuckinmygarage6220]

"Mild 700+ horse...." 😂 Seriously, though: U spoke about compression. What is the best way to test? I'll number what I think: 1) warmed up engine? 2) pull out all plugs 3) fix throttle plates fully open? 4) crank 4 or five times- needle seems to stop advancing? Mild cam(not RV ☺) Please advise. Thank you.

[@vinylcrafters4758]

Good explanation, but the bottom line is try both and let your engine tell you which one it likes!

[@spudthompson1414]

I run a lock out with a 7al MSD on my Hemi 512in it works great 👍.

[@johnmilner7603]

Note that during the HP wars 1962-1970, I.E. 1967-72 Z/28’s, they never had a timed port on the Holley for a good reason. “Ported vacuum" was strictly an early, pre-converter crude emissions strategy, and nothing more. The vacuum advance still worked at steady-state highway cruise (lean mixture = low emissions), but it was inoperative at idle. Use manifold vacuum if you have a performance engine.😢

[@teamh12oneracing7]

Finally, all the information I've been looking for. Well explained, thank you! Now, for tuning with a Vacuum gauge, we need to hook to Manifold, correct?

[@MuscleCarSolutions]

Nice! Glad you found it useful!

[@Dr_Reason]

Manifold vacuum is correct for a vacuum gauge. The port vacuum will read zero at idle.

[@arndtbaslund6030]

"Ported" is also a way to reduce NOX emissions at idle. Even EFI cars have it: a switch that retards IGN timing, only at idle. On old US cars, I always try full vac first, then go back to ported if I can't get it right. Fords in particular are sensitive to vac advance, factory settings do not work anymore with the available pump gas here in the EU. I usually end up with only 5 degrees of vac advance, and full mech advance as late as 3200 crank rpms.

[@TheThirdWheel618]

My truck ran the best using timed vacuum a lighter front spring on the dist and about 2_4 more initial timing it took off like a rocket 🚀 although the exaust was 50 percent louder and it ran hotter I didn't like that part of it although I could get a great AFR on my wideband , idle cruise WOT . Manifold vacuum I had to buy a adjustable vacuum advance to use manifold vacuum.

[@jollywrencher1163]

Manifold vacuum if you're tuning for an efficient motor and not an emission band-aid. Runs cooler, less gas, more vacuum, less throttle angle, the motor tells you what it wants. GM engineers knew it and put in a work around temp switch to change back to manifold from ported to keep from overheating. This is an old video so I hope you've seen the error of your ways lol.

[@MuscleCarSolutions]

What aftermarket carburetor company recommends or sells a ported vacuum switch? Go read up on those god awful things. 😂 Most had a high temp before they would switch over. No one wants to run 225 in their street car and if memory serves me correctly, that’s around where the GM one switched. Ported for street and mild driver, full manifold with an aggressive cam set up. You’re spot on. The engine will dictate what it demands. 70% of street driven vehicles operate much better with timed and a good initial timing set up. It’s those long exhaust duration cams that automatically go on full manifold.

[@jonmartin2624]

I've been revisiting this debate as i need to decide on things while my 70 nova is undergoing restoration. Motor is 355, 9.7 compression, sr torquer heads 170cc runners, 202/196 valve, 480/230@50 110 lsa cam, tunnel ram with dual avs2 500's, 3.73 gears with muncie wide ratio 4 speed. I'm thinking of running 16° initial, 37° total, and 16° manifold vacuum advance. I have heard tunnel rams like lots of timing, and would love to hear your thoughts of if I'm in the ballpark.

[@MuscleCarSolutions]

You’re absolutely thinking the right way. A two four set up likes a lot of timing. That cam profile is moderately aggressive though on a two four motor I’d prefer a split pattern cam so you can help get that exhaust out. If you’re asking about ported or manifold vacuum, in this case I’d go with full manifold and pray for the best with that cam. An AFR is going to be your best friend. You can use it as just an adjustment tool but having a live reading in the cabin will let you monitor it real time and see if you find spots where it goes way rich.

[@jonmartin2624]

Afr is definitely on the list. Thanks again, this is without a doubt my favorite channel and I've learned a ton here!

[@MuscleCarSolutions]

@@jonmartin2624 best of luck! You’ll be thankful for that AFR.

[@MuscleCarSolutions]

@@jonmartin2624 and thank you for the kind words. I do appreciate that.

[@brocluno01]

Look into the history of advance. Early on, it was manual with a lever - you did it as you drove. Then came vacuum advance and things got easier. Ported vacuum advance was never available until the late 60's and early 70's. So from the 30's to the late 70's it was always manifold vacuum. The biggest reason to use manifold vacuum is to help with with lower engine temps at idle. If you are using manifold vacuum you are not opening the transfer slots on the carb, so more timing with leaner idle. With ported vacuum you have to adjust the idle up with the throttle idle screw, partially opening the transfer slots and running more fuel. The vehicle will idle hotter and your fuel consumption will go down. However this is OK if you have a performance motor with a cam. You have no reliable vacuum from the manifold at idle and your idle has to be higher anyway. The lope from the cam will be amplified by the swinging vacuum signal to the vacuum advance. The other reason to use ported is to avoid the slight dip in timing when you flat foot it off the line with manifold vacuum. For drag racing (even street racing) the initial timing and slightly richer mixture with the transfer slots open is the best way to get reliable "leave" 😁 But not the best overall fuel economy 🙃

[@charlespartak2435]

Ok.. how about setting an adjustable vac port distributor ( msd streetfire), when ,why and how ,please.

[@biastv1234]

Good stuff. Vacuum advance is load determined. Mechanical is load related. On the highway, light load equals max advance, on the strip up it for a quarter of a mile, mechanical advance or lockout.

[@mickangio16]

Mechanical advance is engine SPEED related.

[@Frank-mt4qf]

Great info. Very helpful. Love your channel. Thank you

[@MuscleCarSolutions]

Glad it been useful! Thank you!

[@ghtrcp7554]

Great video.. I have locked out distributor, on blown my 383, with msd 6al-2 programmable, can i use vacuum advance?(i want 26 initial and 34 total). Or should i cancel vacuum advance? I want good throat reponse.. thank you.. how do we adjust distributor and crank degrees for the first start?

[@Killer9v]

Thanks from jamaica 🇯🇲

[@colbylaing5187]

Excellent explanation 👌

[@vitodelorto1796]

this is a really good explanation.

[@onehot57]

Have you done a video on phasing your rotor?

[@MuscleCarSolutions]

I haven’t and I might down the road when I go efi on the big block going into the Chevelle. Nothing planned anytime soon though.

[@jima5078]

68 mustang, Ford rebuilt 351w, Mild cam, Holley 600 can, MSD distributor, MSD 6AL. Runs fine in town and cruise speed, after running 30 - 40 minutes on interstate at 70-75 mph, then floor it, it stalls and sounds like misfire. I let off the throttle and she limps back but only if I lower speed to 40-50. What’s gives?

[@jamesgreene9998]

check coil

[@solarflare4259]

I am a noobie to this and I need to ask... I Have a '86 Bronco with a 351W and a C6 AT I'm currently working to restore .I intend to use an AVS2 1906 Edelbrock carburetor on it since the original Holley 4180-C was missing. Should I use the carb timed port , connecting a vacuum hose to distributor for street drive? Which vacuum hoses should I hook up to the carburetor and which ones I need to plug for street use? It also has the "hat" style air cleaner; do I need to keep it or use an "open air cleaner? Thanks!.

[@MuscleCarSolutions]

For street use I’d start with the timed port as the video points out. Which other ones you’ll need and which ones you need to plug is something you’ll need to figure out. As far as the air cleaner goes, I don’t know what a hat or open style is.

[@helihoot]

On my Holley if I'm not using the timed port does it need to be capped? Also on this Brawler there is a hole in the other metering block. What is it for?

[@frankglasgow]

What happens to timing when you are running a long rod , long dwell piston engine such as a 351m?

[@phogandivephogandive3885]

It shouldn't change much. The piston will spend more time near TDC during crankshaft rotation, but the time it takes the fuel mixture to burn won't be different, so you'll need to ignite it the same number of degrees before TDC.

[@raymondmenendez6499]

I'm not a mechanic, but my mechanic for my 1970 C10 with a small block set me up with a manifold vacuum, there's a vacuum line on the distributor that's is plugged off--- is it difficult to just set up the distributor of timed advanced? Can I do it in my driveway? The truck is automatic with a mild cam--- thanks for your time in advance 😀

[@MuscleCarSolutions]

Absolutely you can do that yourself and in your driveway and absolutely you should. You need that ability to adjust timing as the engine is demanding it. What type of distributor do you have? Is it an aftermarket one of a stock type?

[@raymondmenendez6499]

@@MuscleCarSolutions aftermarket, I've been playing with the timing because of pinging and detonation accruing on hard throttle. I am running 93 Octane with a Octane boost additive. Not much, just bringing the Octane to probably 95. When I advanced the initial timing to just around 8, I'll get a high idle which in turn puts my engine into a dieseling mode. Like I said I'm not a mechanic, but after maybe 4,5 different mechanic, I'm putting my hands into the fire and maybe I can make myself happy

[@MuscleCarSolutions]

For a mild cam street car, I’d unlock that distributor (assuming your mechanic locked it out) and go with the engine vacuum to advance your timing.

[@raymondmenendez6499]

@@MuscleCarSolutions i don't know if it's locked, I'll look it up on the internet. Thank you for your time-- hope Santa claus brings you something good for Christmas 🖖

[@65sohc]

You need to know how much mechanical advance the distributor is supplying. To determine this you need a dial back timing light. Disconnect the vacuum advance and rev the engine to the point where the timing is no longer advancing, somewhere in the 3000-3500 rpm range.. That is your total mechanical timing. On a smallblock Chevy it should be in the 32-36 degree range. Once you have set the total mechanical advance see what your timing is at idle. This is your new initial timing setting. Say you find that initial timing is now 10 degrees. If your total timing from above was 36 degrees, 36-10=26 degrees mechanical advance in the distributor. I would go through this procedure and then drive it with the vacuum advance still disconnected to see if it pings. If it does, back off timing two degrees and try it again. Once you get it to the point where it doesn't ping reconnect the vacuum advance to the timed port and retest. The reason it is dieseling is because the manifold vacuum at idle is advancing the timing and raising rpm, so you need to either back out the curb idle screw or switch to ported vacuum.

[@ck1insac]

Just got my DUI Chevy street / strip distributor. Have a Brawler 670 and a Comp Cam 224/230 @ .050. and 110 lobe separation. New engine not broken in or started yet. Would appreciate your opinion on what's best for initial break in, timed or manifold vacuum.

[@MuscleCarSolutions]

You’ll be using timed vacuum going forward, there’s no reason why you can’t use it for initial break in and during your first 3-400 miles of ring break in. If that’s a flat tappet cam, your concern should be all the things we covered in our flat tappet video on how to have a successful process.

[@ck1insac]

@@MuscleCarSolutions thanks for the quick reply! This is a roller set up, not flat tappet. Appreciate your channel very much!

[@MuscleCarSolutions]

@@ck1insac you’re already set for success then! Use a good formulated break in oil for that whole 3-400 miles and get the rings broken in properly and you’ll be well on your way! Thanks for watching. Very much appreciated.

[@Spawndukes]

Timed vaccine makes the exhaust hotter at idle. Warms up the carb and the cat faster. Cold weather warmup time is the purpose. That’s it.

[@Nomad-376]

Thank you Sir . Your awesome , so this would create the rich mix smell at idle with higher comp and 246 @ 50 cam

[@MuscleCarSolutions]

That’s a pretty aggressive cam. I would lock out the distributor and run the advance through a spark box.

[@Nomad-376]

@@MuscleCarSolutions Thank you for the reply , just ordered the msd 6al. Goofy question but the dist. I have is adjustable with an an allen wrench . if i turn that in will that help ?

[@Nomad-376]

@@MuscleCarSolutions nvm i see theres actually a kit now

[@bmclaurine]

Ported and manifold vacuum are the same - except at idle. Connecting to manifold vacuum is better because the engine needs more timing at idle which ported cannot supply. The engine will idle cooler.

[@MuscleCarSolutions]

It’s a bandaid way of adding timing at idle. Set the timing with the distributor for initial and all in and let the vacuum advance the timing as load is introduced. Taking that away isn’t a help to the engine, it’s a hinderance. Unless you have a very aggressive cam profile and need that artificial advance to help keep the idle speed under a little better control. Most street cars perform much better with ported vacuum advance. Throttle response especially.

[@bmclaurine]

@@MuscleCarSolutions Manifold vacuum is a "bandaid" and ported is wonderful ? That's how you analyze something logically ? No one's forcing you to run a cooler engine.

[@MuscleCarSolutions]

If you limit yourself to only one option, you’re restricting the abilities. Most street cars are better tuned with ported. Some will like manifold better. All depends on cam specs. Now if you follow your logic (while other topic of conversation) that more timing equals a cooler running engine, then why not run initial at 20 degrees? 30? 40? You’re actually thinking of retarding the timing will help an engine run cooler. One last little detail to consider. If ported never works, then why do all street aftermarket carburetors still have that option? It would be cheaper from the manufacturing side to not cast for it, drill it and hammer in a fitting. They’d have eliminated it decades ago if that were the case.

[@bmclaurine]

@@MuscleCarSolutions I'm not opposed to ported. Ported became the rule because emissions are reduced when the engine runs hotter at idle.

[@gabej3705]

Question: when adjusting the carb idle mixture with a vacuum gauge I connect the gauge to the manifold VACUM yes?

[@MuscleCarSolutions]

Full manifold vacuum, yes absolutely.

[@lordsauto]

Hi thanks for info whats ur set up? whats ur initial ? I have 350 chevy stock. I have mine 36 total manifold vacuum. Runs good but when hooked to timed port it runs bad.

[@BuddyHolly58]

With vac you should have 47-52 degrees

[@jairosilva925]

Thank you for the video bud! 💯👌🏻

[@MuscleCarSolutions]

You’re very welcome!

[@steelcitycaprice.899]

AWESOME post 😎

[@wmdbowman]

WHAT ABOUT COMPRESSION AND FUEL OCTANE

[@davidreed6070]

If you use ported vacuum on a gm you are messing up. The advance is centrifugal, you can't have both under acceleration.

[@MuscleCarSolutions]

If that were the case, why did GM have vacuum and mechanical advance setups in those distributors and use a ported vacuum source?

[@slewfoot6608]

@@MuscleCarSolutions emmissions?🤔

[@canalm4ch4d03]

@@MuscleCarSolutions if im not mistaken, the 73 nova with a 327 had a manifold vacuum advance from factory, why?

[@aliqadri4672]

You mean 2 step or rev limiter can only run on locked distributer..??

[@ahmadaldahoud1719]

Hi there , I have a stock Camaro 78 with 350cu engine with 4 speed manual what you recommend? As I searched I found factory connected to full vacuum.

[@MuscleCarSolutions]

It’s it’s stock then start with timed and tune there. If you want to try full manifold, then try it and see if you can tune though it. If it’s a stock engine, you’ll have better success on timed.

[@ahmadaldahoud1719]

@@MuscleCarSolutions I feel the engine run smother with timed at idle i tried the full manifold the idel keep changes and rise to a 1000 rpm maybe after setting the timing with time gun I need to connect the vacuum advance and adjust the idle screw is that correct.

[@bingbangbong2552]

Please point to whats manifold and whats port and how to hook up the gauge. Very confusing.

[@MuscleCarSolutions]

Timed is higher, manifold is lower. Want to confirm what ports are which? Remove the carb or TB and squirt some carb cleaner or wd40 into one and view the throttle bores. If it’s timed the hole it comes out of will be above the throttle plates. Full manifold is below.

[@bingbangbong2552]

@@MuscleCarSolutions remove the carb? Take it of the manifold? Whats TB? Can you do a video for idiots? I have a 72 F250, 5.9L 360 New carb from Napa. By reputable mechanic. I Have done all the timing except using pressure guage on port or manifold. 71,000 original miles. Maybe I should try increasing to 10btc or more. Put in Pertronix III. Could the distributor itself be to worn on the octagon points that open and closed the points/magnet?

[@aliqadri4672]

10:18 why it makes richer..???

[@tmc.318]

Same question here. Manifold port brings in more advance at idle and gives more time to burn which allows you to adjust idle even leaner. Retarded timing actually burns more fuel but reduces exhaust gasses.

[@silverseeker1233]

You are correct; manifold vac burns less fuel at idle. Incorrect timing causes overheating in many muscle cars; guys run larger radiators and fans; but correct timing would often resolve their issue. When set on manifold vac and lean at idle; you can reduce off idle stumble via larger accel pump nozzle size. ‘67 Mustang 289 with mild cam. Do your baseline and mech timing curve first; then tune the vac canister. You will be able to cruise down hiway on idle circuit once you get it set correctly!

[@kevinkirkconnell5892]

Thanks finally making sence to me

[@larryw5429]

Problem I have is with manifold vacuum I can't get my idle as low as I want it and if I decrease the timing it doesn't work as well higher rpm!

[@honestabe7349]

Check that your throttle plates seal fully

[@johnweaver8470]

Just curious do gear drives send vibrations through the distributor?

[@MuscleCarSolutions]

Yes. Extremely harsh on distributors.

[@toddrhine7648]

Very interesting, thanks much! Was wondering if you have a video on how to set the initial and total timing with good visual/ verbal methods. I have that same Edelbrock carb on an Edelbrock performer intake Manifold running on a possible stock 350 Chevy engine (don't know anything about the engine) as it's a different motor from another vehicle when purchased. Will subscribe & like to your channel if you can help me here! Thx much.

[@MuscleCarSolutions]

I have some ignition videos planned for this summer.

[@toddrhine7648]

​@MuscleCarSolutions Great to hear that! You may want to discuss about setting your carb first b4 setting your types of timing. Thx much

[@MuscleCarSolutions]

@@toddrhine7648 ah but timing isn’t a fixed adjustment. It’s made through out the carburetor tuning process. They’re done together, not independently of each other. Stay tuned!

[@CLINTSTER77COX]

After a 1/4 mile run is it helpful to have timed vacuum so that as much timing is taken out for instant cooling with retard vs manifold vacuum. Been playing around with it last few months.

[@MuscleCarSolutions]

Not sure I follow. You're making a 1/4 pass, then manually switching from manifold to timed vacuum?

[@lordsauto]

My car seems to idle better with manifold.

[@MuscleCarSolutions]

Every set up is different!

[@DANTHETUBEMAN]

But you could go back to timed vac,, and advance your distributor and probable be back at smooth idle

[@mickangio16]

@@DANTHETUBEMAN you're right, but then you also advanced your total ignition timing. Best to modify distributor for less mechanical advance to put your idle speed timing where you want it other than relying on vacuum advance to do so.

[@michaelg6890]

16:55 "hopefully not a gear drive" Lol that made me laugh. Just yesterday i ordered a chain driven timing set to replace my gear drive the previous owners installed on my 1984 k10 with a 400sbc. That thing is ridiculously loud, it's annoying. Why do you not like them? Same reason or?

[@MuscleCarSolutions]

Noise I don’t mind. The harsh treatment of the valvetrain I do mind. I’m more of a function over anything else kind of guy. But I’ve had a gear drive before. You want to hear a loud one. I have a video from 1995 of my Chevelle with a B&M gear drive. Super loud!

[@michaelg6890]

@@MuscleCarSolutions interesting, I've read quite a bit about them but I'm not entirely sure what you mean about harsh treatment of the valve train. Could you explain? Although i do remember one article saying that the gears transfer combustion harmonics to the valve train, so I'm guessing that's what you mean?

[@MuscleCarSolutions]

@@michaelg6890 the gear drive is gear to gear. There is no forgiveness. The torsional harmonics that the crankshaft sees travels through the gear drive and to the cam. This can be a problem on many levels. Depending on the core material, those harmonics can play havoc on the integrity of the cam. Brittle materials like cast and some tool steel cores don’t like a lot of movement. They are brittle materials. Cast cores are the most popular street core material. If you’re running hydraulic lifters, they can absorb a little of that added harmonics but that’s not their job. Anything that interferes with the operation of the lifter can have a negative affect on general operation and lash. Race application where it’s one thing only - wide open throttle for a few seconds, no problem. Asking the valvetrain to work with it in a street application is only asking for problems.

[@daveski4496]

Was wondering why you said "hopefully not a gear drive" ?

[@MuscleCarSolutions]

There is no benefit to running a gear drive on a street car - ever. Absolute garbage. Horrible for the valvetrain.

[@daveski4496]

@@MuscleCarSolutions i wasnt aware of that. How is it bad on the valve train?

[@MuscleCarSolutions]

@@daveski4496 the way a valvetrain makes power is to stay under control. That’s why spring technology has changed to help control harmonics. Why pushrods have gotten more hi tech with thicker walls and diameters to control the harmonics and flex that they can cause. What happens when you take that forgiving chain driven timing set off and put a solid gear driven set on? All the harmonics from the crank are free to travel back to the valvetrain causing havoc.

[@daveski4496]

@@MuscleCarSolutions i see, well thank you for educating me on this and all of your excellent videos. I really enjoy tuning in to your channel ,always learn some good stuff and hope you keep on clarifying and educating us fellow motor enthusiasts.

[@mickangio16]

Not to mention the obnoxious sound😖haha.

[@robertclymer6948]

What is the difference between Manifold Vac and Ported Vac? Thanks much!!

[@Tj1983coggin]

Only difference is ported will not have vacuum at idle. Meaning if distributor is connected to ported it will run base timing til you give throttle. Will be the same performance everywhere’s else, from off idle to wide open.

[@apachebill]

Ported. Always. Limit distributor’s mechanical advance if more initial is needed. Why? Hook a vacuum guage to manifold vacuum and blip the throttle. It goes to zero and comes back. So does your timing. Right on launch. Manifold vacuum rips out all that advance right as you tip in. Then tries to put it back. Then as engine speed and manifold vacuum is decreased it pulls it out again. It absolutely destroys your launch and 60 ft times. Ported. Always. And that is why. Will manifold work to give you more advance at idle? Yes! It will give you better idle, better cooling at idle. Yes. But it destroys the launch. Better to get the initial you need from the mechanical advance and add vacuum advance up to 52° total on ported. If you want to win. I’m on 30° initial. 6° total mechanical. With 14° of vacuum advance on port. 50° total cruising timing. 36° at wot . Runs like it was built by Satan himself.

[@michaelsnively3621]

@@apachebill so what exactly are you driving, and what is your carburetor and manifold set up?

[@reevesautomotivefarm9614]

Unfortunately there is no legitimate use case for ported vacuum. if this were the case before a emitions controls carburators would have had pointed manfull vacuum. Also your late model fuel injected engines would apply this and have very low timing at idle but they do not, they are 20 to 30° just like your carborated engine with manifold vacuum.

[@MuscleCarSolutions]

You’re a bit misinformed of what that function is for. Vacuum advance has a direct effect on the distributors mechanical advance. If you run full manifold vacuum, you lose that adjustment from low rpm cruise to a condition with more load that demands more advance. You’re already at that capacity at that point. Ported vacuum allows both systems to work as intended. Ported brings in advance as the engine starts to see load, no full vacuum advance at idle. If ported wasn’t needed, no carburetor manufacturer would continue to put it on their street carburetors. They would have cut that cost decades ago.

[@reevesautomotivefarm9614]

@MuscleCarSolutions More load requires less advanced not more. also prior to 1967 there was no carburators made with ported vacuum advance. it was only ever put on carburators to make the engine run harder for emitions controls. It is currently included on carburators so they can meet later emission requirements and still be OK to run on the street.

[@aliqadri4672]

What is epa side??

[@robertclymer6948]

They called it Timed Vacuum port.

[@johnterpack3940]

Theory is fine, but evidence is better. Just watched a video with a very simple, clear demonstration of why to always use manifold vacuum. All he did was show what happens on a vacuum guage with each port. Manifold vacuum gives you advance at idle to compensate for the lean mix. As you get into the throttle, that advance goes away. Your mechanical advance should be curved to come in pretty quickly off idle as the vacuum drops off. The two advances don't add together, they cover different needs. Think of vacuum advance as the idle circuit of the ignition system and mechanical advance as the main jets. Using ported vacuum leaves you with zero advance at idle and then both advances kicking in when you hit the pedal. That makes no sense.

[@MuscleCarSolutions]

Having more advance on an engine under no load (idle) makes no sense. It’s all about tuning and giving the engine what it wants when it needs it.

[@johnterpack3940]

@MuscleCarSolutions It makes perfect sense. At idle you get very poor cylinder fill. So the mixture in the chamber burns slower and can't produce as much pressure as a max VE charge would. If you don't advance timing, the flame will just warm the piston as it chases it down the cylinder.

[@MuscleCarSolutions]

Any lack of cylinder fill is inconsequential when there is no demand for power (load). Any lack of or excessive fuel is easily adjusted out. Unless you have some need to build full power or max efficiency. Now WOT if you want to find the best timing and fuel/air; thats worthy of the additional timing, tuning and the extensive data logging required to make those adjustments. Just like every other part and system on an engine, there is no one size fits all single answer. If ported works better, use it! If full manifold vacuum is needed, it’s there. Neither are exclusive.

[@lightninsadventures2692]

Just a mild 700hp big block lol

[@rodneymckinley9912]

Why not buy a gear drive ???

[@MuscleCarSolutions]

Worst thing you can do to a valvetrain. Gear drives on a street car are trash.

[@11Xshadowolf]

When you associated timed port with EPA I knew then to cap that shit off and run manifold, I refuse to comply or negotiate with terrorist organizations ... great video !

[@dogmanXR600]

700 hp is mild??

[@CLINTSTER77COX]

I do have a question. We have a blueprint 350 crate . Dyno says 405hp ( sold as a 373 hp at summit. )$ 2799.00 if you want to see exact specs . Anyway can’t get off the line good with a 650 cfm AVS carb . Had to go down to the 500 cfm . Do you think the 650 is a loss cause or maybe play with another torque converter.

[@MuscleCarSolutions]

Whats the cm specs? What converter do you have? 650 should be fine if its making 400hp.

[@CLINTSTER77COX]

@@MuscleCarSolutions Vortec Cam Type: Roller .495/.502 lift 221/226 duration @ .050, 110 degrees LSA Using 1.5 rockers 1900 stall converter.

[@MuscleCarSolutions]

@@CLINTSTER77COX thats a rather mild cam. Stall matches it just fine. Whats your initial and all in timing set at? Have a hesitation off the line? Does it clear up and start pulling?

[@CLINTSTER77COX]

@@MuscleCarSolutions 9 or 10 without vacuum advance . Total timing is at 34 degrees. Yes it almost stalls out at launch with the 650cfm in it . It clears up once you get it moving . We ran a slower 1/4 mile with the 650 vs the 500cfm . But yet had a higher mph with the 650 . 13.01 second 1/4 mile .

[@MuscleCarSolutions]

@@CLINTSTER77COX more initial timing. 12-15

[@jds1906]

the video would have been a lot better without your hand waving around for 23 minutes, with all due respect it is very distracting and detracts from the presentation :/

[@MuscleCarSolutions]

I’m so very sorry this upset you so much. I hope you’ll be ok. 😟

[@patton9696]

Reduce your video in half.

[@MuscleCarSolutions]

@@patton9696 nope!

[@patton9696]

@@MuscleCarSolutionsok….