The Ultimate Vacuum Advance Video Part 1

[@kkyler9582]

TIMING AND VACUUM ADVANCE 101 by GM Engineer. The most important concept to understand is that lean mixtures, such as at idle and steady highway cruise, take longer to burn than rich mixtures; idle in particular, as idle mixture is affected by exhaust gas dilution. This requires that lean mixtures have "the fire lit" earlier in the compression cycle (spark timing advanced), allowing more burn time so that peak cylinder pressure is reached just after TDC for peak efficiency and reduced exhaust gas temperature (wasted combustion energy). Rich mixtures, on the other hand, burn faster than lean mixtures, so they need to have "the fire lit" later in the compression cycle (spark timing retarded slightly) so maximum cylinder pressure is still achieved at the same point after TDC as with the lean mixture, for maximum efficiency. The centrifugal advance system in a distributor advances spark timing purely as a function of engine rpm (irrespective of engine load or operating conditions), with the amount of advance and the rate at which it comes in determined by the weights and springs on top of the autocam mechanism. The amount of advance added by the distributor, combined with initial static timing, is "total timing" (i.e., the 34-36 degrees at high rpm that most SBC's like). Vacuum advance has absolutely nothing to do with total timing or performance, as when the throttle is opened, manifold vacuum drops essentially to zero, and the vacuum advance drops out entirely; it has no part in the "total timing" equation. At idle, the engine needs additional spark advance in order to fire that lean, diluted mixture earlier in order to develop maximum cylinder pressure at the proper point, so the vacuum advance can (connected to manifold vacuum, not "ported" vacuum - more on that aberration later) is activated by the high manifold vacuum, and adds about 15 degrees of spark advance, on top of the initial static timing setting (i.e., if your static timing is at 10 degrees, at idle it's actually around 25 degrees with the vacuum advance connected). The same thing occurs at steady-state highway cruise; the mixture is lean, takes longer to burn, the load on the engine is low, the manifold vacuum is high, so the vacuum advance is again deployed, and if you had a timing light set up so you could see the balancer as you were going down the highway, you'd see about 50 degrees advance (10 degrees initial, 20-25 degrees from the centrifugal advance, and 15 degrees from the vacuum advance) at steady-state cruise (it only takes about 40 horsepower to cruise at 50mph). When you accelerate, the mixture is instantly enriched (by the accelerator pump, power valve, etc.), burns faster, doesn't need the additional spark advance, and when the throttle plates open, manifold vacuum drops, and the vacuum advance can returns to zero, retarding the spark timing back to what is provided by the initial static timing plus the centrifugal advance provided by the distributor at that engine rpm; the vacuum advance doesn't come back into play until you back off the gas and manifold vacuum increases again as you return to steady-state cruise, when the mixture again becomes lean. The key difference is that centrifugal advance (in the distributor autocam via weights and springs) is purely rpm-sensitive; nothing changes it except changes in rpm. Vacuum advance, on the other hand, responds to engine load and rapidly-changing operating conditions, providing the correct degree of spark advance at any point in time based on engine load, to deal with both lean and rich mixture conditions. By today's terms, this was a relatively crude mechanical system, but it did a good job of optimizing engine efficiency, throttle response, fuel economy, and idle cooling, with absolutely ZERO effect on wide-open throttle performance, as vacuum advance is inoperative under wide-open throttle conditions. In modern cars with computerized engine controllers, all those sensors and the controller change both mixture and spark timing 50 to 100 times per second, and we don't even HAVE a distributor any more - it's all electronic. Now, to the widely-misunderstood manifold-vs.-ported vacuum aberration. After 30-40 years of controlling vacuum advance with full manifold vacuum, along came emissions requirements, years before catalytic converter technology had been developed, and all manner of crude band-aid systems were developed to try and reduce hydrocarbons and oxides of nitrogen in the exhaust stream. One of these band-aids was "ported spark", which moved the vacuum pickup orifice in the carburetor venturi from below the throttle plate (where it was exposed to full manifold vacuum at idle) to above the throttle plate, where it saw no manifold vacuum at all at idle. This meant the vacuum advance was inoperative at idle (retarding spark timing from its optimum value), and these applications also had VERY low initial static timing (usually 4 degrees or less, and some actually were set at 2 degrees AFTER TDC). This was done in order to increase exhaust gas temperature (due to "lighting the fire late") to improve the effectiveness of the "afterburning" of hydrocarbons by the air injected into the exhaust manifolds by the A.I.R. system; as a result, these engines ran like crap, and an enormous amount of wasted heat energy was transferred through the exhaust port walls into the coolant, causing them to run hot at idle - cylinder pressure fell off, engine temperatures went up, combustion efficiency went down the drain, and fuel economy went down with it. If you look at the centrifugal advance calibrations for these "ported spark, late-timed" engines, you'll see that instead of having 20 degrees of advance, they had up to 34 degrees of advance in the distributor, in order to get back to the 34-36 degrees "total timing" at high rpm wide-open throttle to get some of the performance back. The vacuum advance still worked at steady-state highway cruise (lean mixture = low emissions), but it was inoperative at idle, which caused all manner of problems - "ported vacuum" was strictly an early, pre-converter crude emissions strategy, and nothing more. What about the Harry high-school non-vacuum advance polished billet "whizbang" distributors you see in the Summit and Jeg's catalogs? They're JUNK on a street-driven car, but some people keep buying them because they're "race car" parts, so they must be "good for my car" - they're NOT. "Race cars" run at wide-open throttle, rich mixture, full load, and high rpm all the time, so they don't need a system (vacuum advance) to deal with the full range of driving conditions encountered in street operation. Anyone driving a street-driven car without manifold-connected vacuum advance is sacrificing idle cooling, throttle response, engine efficiency, and fuel economy, probably because they don't understand what vacuum advance is, how it works, and what it's for - there are lots of long-time experienced "mechanics" who don't understand the principles and operation of vacuum advance either, so they're not alone. Vacuum advance calibrations are different between stock engines and modified engines, especially if you have a lot of cam and have relatively low manifold vacuum at idle. Most stock vacuum advance cans aren’t fully-deployed until they see about 15” Hg. Manifold vacuum, so those cans don’t work very well on a modified engine; with less than 15” Hg. at a rough idle, the stock can will “dither” in and out in response to the rapidly-changing manifold vacuum, constantly varying the amount of vacuum advance, which creates an unstable idle. Modified engines with more cam that generate less than 15” Hg. of vacuum at idle need a vacuum advance can that’s fully-deployed at least 1”, preferably 2” of vacuum less than idle vacuum level so idle advance is solid and stable; the Echlin #VC-1810 advance can (about $10 at NAPA) provides the same amount of advance as the stock can (15 degrees), but is fully-deployed at only 8” of vacuum, so there is no variation in idle timing even with a stout cam. For peak engine performance, driveability, idle cooling and efficiency in a street-driven car, you need vacuum advance, connected to full manifold vacuum. Absolutely. Positively.

[@83glxcrusin97]

My distributor is set to have a mechanical advance limited to 15 degrees in factory form.. can be adjusted.. does that also limit the vacuum advance to 15 degrees?.. still learning this stuff... I have a fully built 306 in my Stang and it ran like shit on 10 degrees base.. and also at 13 had a major lag.. I'm aiming for 34 ish fully in so I bumped it to 19 degrees base taking in the 15 degrees the dizzy will advance.. runs way better now.. doesn't seem to ping as they say and the straps on the plugs look ok also.. any insight would be great!! You seem to know what you're talking about!! 👍

[@Charlie_Prinz]

Very well written. 👍👍👍👌👌 . Very interesting.

[@donaldhill2775]

Best thing I’ve read concerning this subject and I’ve read quite a lot whilst struggling to setting up a modified sb Ford, thank you sir !

[@kloeppky6613]

I have watched a lot of David’s videos and read his Holley book and the way you guys explained it finally makes sense to me. Thank you.

[@UnityMotorSportsGarage]

Thanks for watching and the kind words! im glad you enjoyed it

[@rightsidelanechoice7702]

David talks a lot better when he’s not worried about being on camera, just conversing with you, you’d never know he had a brain injury. It makes me feel a lot better for him watching this video.

[@UnityMotorSportsGarage]

This video was just prior to his surgery.... He does better in a conversation type setting Thanks for watching Andy

[@nocandopdx]

I thought he talked just fine honestly, got interrupted al little much though

[@dustinunderwood1662]

David vizard is a legend ! What a life he’s lived ! Hats off to you Mr vizard

[@gibbsey9579]

Your timing is perfect. (Pun intended). I am currently reading David Vizard's book, Super tune and modify Holley Carburetors. And have just come across the vacuum advance chapter. When this guy talks, I listen.

[@UnityMotorSportsGarage]

Thanks for coming over and watching! He is a wealth of knowledge and he has taught me a great deal over the years... CASPER is a reflection of those things! CASPER version 3.0 will be even better with MIXED UP BOSS!

[@havoc9926]

great video.vizard is the man i know he likes single pattern cams.another topic though.im glad sum 1 put up a video saying the benifits of manifold vacum and why u should use it.im so tired of all these little jerk offs on u tube making video,s saying ported is the way to go.

[@UnityMotorSportsGarage]

Thanks.. The main takeaways is 1) you should be running a Vacuum Advance 2) we should be trying to give the engine what it wants for an advance curve vs what we think it should be 3) you need a way to adjust your vacuum advance 4) Ported Vacuum was only created as a emissions bandaid. I'm glad you enjoyed the video.. please help us spread the word about the channel! Andy

[@markcarter78]

This video was great!!! This needs to be watched by all motorheads, why you ask? I have a friend that is a great mechanic and he too was lost when it comes to Vac Adv. I myself just learned this only about 5 years ago myself. It works just like you guys say. I cant wait for the June class. I will be there with my ears and my notebook. Thanks Andy and David. You guys rock!!!!!

[@twgarage-terrywatson1672]

Finally, someone else saying what I have been doing for years. Full manifold vacuum. 100%, better fuel economy, runs cooler at idle. All makes sense. Great video, considering the source. The BS absolutely stops here. Great job.

[@UnityMotorSportsGarage]

Thanks for the kind words TW Garage! I'm glad you enjoyed it Andy

[@yeboscrebo4451]

I don’t understand. If I switched to manifold, I’d have to retard my initial timing so my truck would run at idle. Then after the throttle blade opens up the vacuum advance timing would be the same as it would have been on ported. However, WOT the mechanical timing wouldn’t be sufficient to bring the total timing up to where it needs to be after the initial timing was retarded. Ported advance makes more sense to me. What ami not getting?

[@GaryH-pw9cm]

@@yeboscrebo4451 That is what I would think also. I understand the part about full vacuum advance at idle causing a cooler running engine when connected to manifold vacuum. Many cars had this thermostatic operated system that switched the distributor from ported vacuum to manifold vacuum in the 70s and 80s before engine management computers. But if your distributor is connected to manifold vacuum, then at wide open throttle there would be low manifold vacuum causing a retarded ignition timing. But using ported vacuum at wide open throttle would have full vacuum for full timing advance. My MSD distributor instructions said to use ported vacuum to operate the distributor vacuum advance. What am I not getting? 🤔

[@yeboscrebo4451]

@@GaryH-pw9cm I’ve since experimented and found out that my truck likes waaaay more advance at idle than I thought so didn’t need to retard initial at all. My FE engine loves 32 degrees at idle. It loves higher initial timing than I though it needed. After switching to manifold and re-tuning, everything got better. My engine was waaaay quieter (I thought it died at the intersection but it hadn’t - it was just quiet), way smoother and way cooler. And my mpgs went into the high teens from the 12 it used to get. Andy was right on.

[@stevewheat9030]

Man, you got that right about Mr. Visard...the guy is a legend!!!! I've been reading his books for almost as long as I've been messing with high performance engines 35+ years and the knowledge that David has is phenomenal...thanks for sharing all this information.... so helpful!! 👍

[@firebirdjone]

Nice to see a couple guys explain how this really works. You're spot on. I've been modifying those vacuum advance units for years to make them do what I need, especially now that a lot of the good cans are becoming discontinued. I'm a manifold vacuum fan as well and remember when manifold vacuum was common until emissions took over. Another excellent video.

[@UnityMotorSportsGarage]

Thanks for the kind words... People don't realize how many cans were offered back in the day.... Now when you get a vacuum advance distributor.. who knows the curve it will provide... Andy

[@blakenorman4822]

So i want to hook my vacuum advance cannister on my distributor up to my intake manifold? Ported would be to hook up my cannister to my carburetor above the throttle plates?

[@UnityMotorSportsGarage]

You want full manifold vacuum.. that way you get the benefits of having proper timing at idle and under decel!

[@softenerguy]

@@UnityMotorSportsGarage there's got to be a better way to explain this. Maybe more on where you want more or less timing at different RPM's or loads. And also why if the vacuum is advancing the timing on idle, then why can't you just have the base timing set there and throw out the vacuum advance all together.

[@davidandrew2610]

Thanks Andy another informative video . Just to throw you a curve ball buddy , here in New Zealand apart from having some of the worst gas in the world and at $ 2.19 a litre 95 octane some of the most expensive ( 100 octane - $2.80 litre ) our 95 is about your 89 our 100 is 95 with octane boost . Our longest straightest road goes for acouple miles the rest is winding , hilly , short distance goat tracks with a few highways . What I have found after extensive economy testing , tuning the rest first then fine tuning the vac adv only improves the off idle response and marginal mpg improvement on a trip , the problem being as soon as you touch the gas it always momentarily rattles regardless how much timing I pull , rich or lean or how much I slow the mechanical or limit the total . Now I set em up with as much timing as the engine wants at idle , what total it likes then slow the curve to suit the gas and driving style . Stock 500 ci 76 Eldorado with my custom headers and exhaust , mr gasket ad vac adv , 17.2 mpg . 69 road runner hot 440 my headers exh , 4spd , 3.5 , 28 tyre - 17.3 mpg . 1988 chev c30 ambo 3 ton , 350 , ported vortecs , isky 270 , headers my exh 400 , 4.11 , 29 tyre 650 spreadbore dp - 18 town , 24 trip . DV will like this one - 65 mk 3 zepher 302 w, 9.5 isky 270 , eddy perf holley 600 , headers my exhaust 5 speed celica , 3.0 9 inch 24 tyre , 31.5 mpg on a trip . 20 / 22 in town cruizing.. Slightly different circumstances . Economy is very important especially here , all in know is a rattling engine is hard on ring lands and bearings and you have to save alot of gas to equal that bill . Cheers Andy lol exuse my rattling on mate and have a fantastic day .

[@UnityMotorSportsGarage]

David thanks for the kind words... That is why if you can have access to a Eddy current Chassis Dyno it makes finding the perfect vacuum advance curve so much easier.. To do the process that David and I spoke about takes a great deal of time and effort.. if you do the testing and find out your readings.. you can call up Performance Distributors and they can match you curve to a vacuum canister! When you buy an aftermarket distributor.. the canister that comes on them most of the time is a weak compromise because they are covering a wide range of engine specs.. from mild to Wild...

[@davidandrew2610]

@@UnityMotorSportsGarage cool thanks for that Andy , yea dyno time here is expensive mate , like everything else at the bottom of the world , almost prohibitively expensive , bit we still have a huge petrolhead community .

[@Ambrosius50]

This is a good video. Probably because the producer understand the basic why vacuum advance was added to cars during the 50's. The physics behind combustion and the development of the flame front coming the a peak pressure in the cylinder aimed to be about 17 deg after TDC. It will vary from cycle to cycle because the time it takes from a needle head size flame to a pea size flame is a great part of the timing, and that is highly dependant of the pressure in the combustion chamber. The higher the pressure, the more rapid growth to a pea size flame. Vacuum advance is added during part throttle, which most of the cruising or daily driving occurs. Low cylinder pressure, to late ignition and too much to burn late in the combustion stork, overheating the exhaust valves and heat (energy) blown out of the exhaust pipe. Ported vs manifold pickup. If you have a modern ignition system able to disregard the vacuum signal below a set rpm, use manifold pressure, if not use ported, as engines does not like a too high advance during start and idling.

[@trailerparkcryptoking5213]

Perfect video! Lots of internet hotrod experts argue that you need ported vacuum because Uncle Bob told them so and he was a master mechanic!

[@v8torqueka578]

Man, this is pure gold, Im a big DV fan, and these days trying to dial in my vacuum advance curve on my 355 sbc using a te Crane vacuum can and limiter plate. Very glad I found this channel and thanks for sharing with us! Greetings from Norway

[@edwardmarculewicz5140]

Just incredible! Almost wizardry, no word play intended!

[@pontiac411]

David taught me the same thing around 2005, I also found that my 2001 and 2009 LS 6 liter engines run about 51ﾟ of timing at steady state cruise on the highway from the factory by using a scan gauge

[@danielgalvan2201]

Interesting. Never heard this topic explained so well.

[@The282mike]

YES My Friend this and your next one are the ultimate vacuum advance videos! David Vizard also has an excellent book out on Holley Carbs that touches on this subject, and is the BEST Holly tuning book that I have ever found! Between the two of them I'm getting fantastic gas mileage on my hotrod big block Chevy! Trust me on this guys, these two know what they are doing! We all need more Excellent videos like this!! from a Subscriber, Mike. Happy Wrenchin!!

[@UnityMotorSportsGarage]

Mike thank you so much! Im just giving away what was freely given to me by David! He has taught me so much over the years im blessed to have him as my mentor but more importantly my friend! Andy

[@tomgrant158]

Wow, excellent video and a very thorough explanation! I really appreciate both of you gents sharing the knowledge.

[@UnityMotorSportsGarage]

I'm glad you enjoyed it! Thanks for watching Andy

[@bryaninwood683]

I have been playing with cars since i was 10 im 55 now ive had this vacuum advance discussion that at times has turned into an argument with experts . ported vacuum needs to much initial advance to comfortably start a high comp engine . no vac advance just sucks the juice .I only ever run manifold vac its the only thing that works im glad i found your channel from watching UTG cheers from down under

[@UnityMotorSportsGarage]

Bryan, thanks for coming over... I don't understand the big argument.. The main thing is to use the amount of advance that the engine wants and not what we think it should be... LOL... Having a properly setup Vac. Advance will surprise many on the mileage that can be obtained.. please help us spread the word about the channel! Andy

[@OriginalSphincter]

alot say timed because when you mash the pedal you "need it most"(timing that is). Just need to fill that hole with fuel via fatter pumpshot or enriched idle/transition circuits, is my opinion.

[@virtuestreams2616]

Fantastic interview and conversation! My first experience involving vacuum advanced involved the secondary advance on my 350 which powered my 1975 Chevrolet Monte Carlo; I learned quickly that this little part was essential to the process of utilizing the energy the engine is capable of creating.

[@UnityMotorSportsGarage]

All one needs to do is look back in history.. before emissions there were few vacuum lines in the engine bay... After 1971 things starting get very complex very quick... Andy

[@rooster68able]

You no ask 3 different engine guys 1 says ported 1 says full manifold. 1 says no vacum there all right to its a individual bases far as im concerned

[@MrTheHillfolk]

14:11 Pilots call it adjusting for lean of peak. Keep dialing the mixture back at cruise until the egt peaks out and starts going down. They usually run em 50-100f cooler than peak and it still pulls good without missing and hiccuping. And food for thought : How can you throw less fuel on a fire, and have it burn hotter ? Winner winner chicken dinner if you said : you can't. Stay on your toes folks , this is where it's at.

[@UnityMotorSportsGarage]

Bingo!

[@TaekwondoFitForLife]

Wow, absolutely enlightening! The long argument, even in my own mind has been solved, always use manifold vacuum. I have been overheating my 383 Stroker small block engine in my 1963 Chevy C10 pick up truck and have been wondering why I cannot get it to run cooler? I know what I’m doing. When I go outside before I take a ride I’m going to switch over to manifold vacuum! I love it! I was so thrilled to find this channel and follow! I found you through UTG.. this is an awesome channel!❤

[@alva1370]

Excellent, thank you Andy and David.

[@UnityMotorSportsGarage]

Thank you for watching! Please Subscribe and help us spread the word about the channel! Andy

[@alva1370]

@@UnityMotorSportsGarage I'm onboard. David Vizard is a big name, thank you for showing us inside his world.

[@UnityMotorSportsGarage]

@@alva1370 it's an honor really.. I appreciate you watching and subbing... Andy

[@gregleenyit]

I'll tell ya what that really was the Ultimate vacuum advance video!!! Thanks to you and David

[@UnityMotorSportsGarage]

Thank you! Thanks for watching please Subscribe and help us spread the word about the channel.. Andy

[@herbslusher4409]

I love a common sense approach! David is royalty to me!! You guys make an excellent team. Kudos!

[@UnityMotorSportsGarage]

Thanks Herb for Watching and the kind words! We will keep them coming... Andy

[@yeboscrebo4451]

So interesting! Thank you for passing on is knowledge

[@UnityMotorSportsGarage]

Thanks for watching! Andy

[@1997LT1Camaro]

Great video. I have a progression ignition distributor on my 440 , it uses a map sensor to do exactly what you are doing, but it alters the vacuum advance dynamically.

[@UnityMotorSportsGarage]

I'm so, wanting to try one of those! It really takes vacuum advance tuning to the next level.. Andy

[@65sohc]

I have Progression Ignition on my 406 sbc. What I did is study the ignition maps for EFI systems like Holley Sniper and Edelbrock and try to emulate those. They are very different than the sort of curve achievable with a conventional distributor.

[@UnityMotorSportsGarage]

I agree... It's a completely different animal and can do some amazing things Andy

[@bobcuomo5122]

Wow....that was great can't wait for part Two.Thank you Andy .

[@UnityMotorSportsGarage]

Thanks I hope you will like it... Andy

[@PTucker0864]

Good info. I was always under the impression that ported vacuum was best to increase advance as the throttle is opened. I didn't consider the need for more timing at idle, then having it go away as you open throttle. Although, with the idle speed adjusted correctly, even though the vacuum goes away for the canister, the mechanical advance weights will take over on acceleration. I have a small block Ford that is using ported vacuum since I built the engine....it runs good...I might switch it to see how much better it might run. 👍

[@dannycastaneda1974]

Love this! Thank you so much for delving into the details. I will be getting into performing these steps on my 65 mustang with MSD E-curve ignition. Gotta get a guage with a long hose . Already have timing light. Wish me luck!

[@briansd2772]

Wow! Thank you! You read my mind! I was just working on this over the weekend. I'm sorting out an adjustable vacuum canister right now.

[@UnityMotorSportsGarage]

That is the key to making it all come together... Having a way to adjust the Vacuum Advance curve to give the engine what it wants...

[@wayneguess7946]

Very informative! Think I will try switching my T Bucket over, I'm on port vacuum now!

[@UnityMotorSportsGarage]

Just as a reminder you will need a vacuum canister that is adjustable to get the full benefit... Thanks for watching! Please Subscribe and help us spread the word about the channel Andy

[@StupidFastTruck]

Another great one. It seems like years ago we would play around with changing the weights and springs on GM distributors to tweak more advance out of distributor.

[@bryanbrumfield3533]

🤯🤯🤯 wow this was awesome! I need a vacuum pump and a project car now haha. I really want to try these tricks lol

[@darylw792]

I have been using manifold vacuum on my 496 BB chevy for several years now. After putting in a 6 speed Tremec double over drive trans in I did highway mileage testing and got 26 mpg. This was with an 850 Demon carb and 3.55 gears in a 1968 Chevelle. I have switched to a Fitech EFI but have not taken any mileage tests yet. With manifold vacuum there is no sacrifice of power that I can see. Just tap the throttle and off she goes and no pinging ever. I may need to try your idea because the way I set up my timing was just guessing. 7 degree initial with an vacuum canister pulling 18 degree adv for 25 degrees at idle and 49 degrees at 2500 RPM. I basically shot for about 50 degrees near my 70 mph cruising speed before got the over drive trans. Now with 70 mph running at about 2000 rpm's I am not sure if I should change anything.

[@UnityMotorSportsGarage]

Daryl, it would be interesting to see the MPG difference between the Carb and EFI setups.. It sounds like you have a great handle on the tuneup! 50 degs is about the max that I have ran and had great luck with it.. Its amazing to hear the engine when it is in its sweet spot.. it almost gets quite..LOL Thanks for Watching! Andy

[@DANTHETUBEMAN]

Great video to get all the actual data on vacume advance requirements for your engine and set up. David is right to record the measurements for 25mph stop light to stop light, and your 70mph freeway speed.

[@cellis6340]

Great video Andy...I have a progressive ignition distributor, how would one replicate this test or determine the correct settings with it?....thanks

[@dadsgarage420]

Lol he looks like Austin powers Dad. Much respect your the man Mr. Visard I’ve learned tons from your videos thank you for your knowledge.

[@MrTheHillfolk]

I remember is a kid in the 80s reading all the car mags , I musta read hundreds of his articles. Odd feeling seeing him in a vid now, it's like someone you know but never met. Always wrote awesome tech articles.

[@edward-x3s6f]

Thanx Andy , David has my Attention Brilliant Man👍

[@UnityMotorSportsGarage]

He has forgotten more than I will probably ever know... I'm very fortunate to have him as my mentor for the past 15 years... Andy

[@mikef-gi2dg]

I'll be damned....Andy is another guy who knows Vizard, and that is the first time I have EVER heard a complete explanation, with history of vacuum advance. I purchased a Chevy crate 260hp 350. I installed a performer cam and intake from the start. If I advanced the initial to the recommended 12 to 16 degrees initial, when it was hot it barely could crank. So I reduced the initial to 4*, then modified the vacuum advance to no more than 10* advance. I went to manifold vacuum and it worked beautifully. Starts easily, idles like a watch, and at cruise it shows 17 to 18 inches of vacuum with practically no throttle at 60-65 mph. It really works, and I guessed at the change.

[@UnityMotorSportsGarage]

It's all about giving the engine what it really wants! It makes a huge difference... Most just ignore or eliminate the vacuum advance.. Thanks for Watching Andy

[@mikef-gi2dg]

@@UnityMotorSportsGarage Hey my vac adv questions are answered, and Andy knows Vizard...I got to watch now. Way back in the late 70's, DV did a story on a factory V8 Monza. DV did his usual tricks and transformed it into a respectable performer. If you get a chance, ask if he remembers that article, I think it was PHR. That was my first taste of DV magic.

[@cbobscountrybunker2312]

Thank you for the awesome information . I have read alot of Davids books, im always excited to get the new ones that come out. Good information is hard to find about these things. Keep em coming.

[@UnityMotorSportsGarage]

No, Thank you for watching! Please subscribe to the channel and the videos will keep coming.. Andy

[@cbobscountrybunker2312]

I have a 302 sbc project in the making, its going into a 81 maliu 4door sleeper. It was a 3speed manual replaced with a close ratio t10. Trying to come up with a solid flat tappet cam to work well with vortec heads extra. It must be nice to have such fine minds to brainstorm with. Where im located , you just get strange looks for bringing up out side of the box ideas.

[@DANTHETUBEMAN]

@@cbobscountrybunker2312 the L97 cam would be nice on that, if your rears are 3:⁷³,, range. You need tourq, I would not go over 240 gyration at 50

[@kevinclancy.]

excellent video and great methods for dialing in optimum vacuum advance

[@UnityMotorSportsGarage]

Thanks for the kind words Kevin... It works.. but it is time consuming! Andy

[@jeffm5475]

Many years ago I played with ported vs manifold vacuum to the vacuum advance. V8 Pinto with 4:11's. Running manifold vacuum at cruise made sense, but it drops to near zero when you hit the throttle. I found ported vacuum worked better on the street. Should we run more initial timing when using manifold vacuum to the vacuum advance to compensate for the drop in timing at WOT?

[@kevinrich9471]

Love this! Is it possible to use a device like the MSD timing box to increase timing in a computerized engine? I have a 1995 Ford F-150 with the 4.9 straight six that I’d love to increase the fuel economy in. Thanks!!!

[@Bhughe4]

Greetings. Saw your comment and even thou its a year late I wanted to share a couple minor tweaks. I daily drive a stock, 1993 F150 4.9 I6. Our trucks have a full computer control distributor with no vacuum advance in addition to having Speed Density vs Mass Airflow Sensor computers. Speed Density is a bit more tricky and finicky to tune than MAF so the things we can do are limited. What ive done to make our old 4.9 a bit more peppy is I have the distributor clocked at about 14 degrees base timing, I use an Accel coil for better spark, run a brass rotor and cap for less electrical resistance, took the ignition module and applied a new high grade heat sink paste. Finally I open the Motorcraft plugs up to .055". It vastly improves the driveability, idle and the ECU and sensors are none the wiser. Happy motoring : )

[@chimpfoos65]

Again your videos are quality and good information thank you SIR

[@UnityMotorSportsGarage]

Thanks for the kind words! Andy

[@philipmazzuca2269]

Another great video Andy

[@UnityMotorSportsGarage]

Thanks !! Andy

[@ihycoi396]

Part I has helped me greatly! I am itchin" for part II.

[@anthonyadams693]

What about a stock pre emissions engine, ported or manifold? What about heating issues at higher rpm’s?

[@johnwilburn]

I’d love to hear more about initial/base timing in part 2. Great stuff, man.

[@UnityMotorSportsGarage]

@Baron Boghosian Thank you so much for the kind words... Im very fortunate to have hooked up with John and Tony.. they both are the real deal... As far as sponsorship that would be amazing.. but I'm excited that you guys are liking my content.. Andy

[@UnityMotorSportsGarage]

@Baron Boghosian hey Brother, when you get over this way... We can make that happen! We will definitely get together!

[@SpeakerKevin]

Great video. Love hearing from the true experts in the field.

[@JohnDoesItAll]

There's so many opinions (as you're well aware) on this subject. I've got a SBC very similar to yours. 13.5:1 compression, 406 cid with a 630 lift solid roller cam, 108 centerline and 42° overlap. Originally built for the track but those days are behind me. My intention is to drive occasionally on the weekends and I'd like to hook up my adjustable vacuum advance. I'm thinking of moving my base timing up and limiting the total mechanical advance so that I have the best of both worlds. What is your base timing and total mechanical advance?

[@terryheimerl8674]

Thank you gentlemen. Another great, informative video.

[@keithcalitri840]

Great video andy now I’m gonna watch part 2. Always GREAT stuff you have for the viewers.

[@jessesyfie7244]

Andy, u favor running the vacuum advance manifold vacuum not ported? I don't have any heating issues at idle but either place u hook them up it's load sensitive and does the same thing to the timing. Just doesn't make sense why u need to advance timing at idle with manifold vacuum? My machinist says that's ass backwards. I had mine to manifold and puts in to much timing to start and kicks back so I went back to ported vacuum like factory had them on my 72 Chevy.

[@calebkey2050]

Great vid man... If I’m understanding this correctly, you’re using the vacuum pump to determine what the optimal amount of timing added by the canister would be? Any tips on determining what the optimal opening point on a vacuum advance would be? I’ve always heard 2” below idle vacuum, but I’m really interested to hear your take on that... Or will I have to wait for part 2 for this wisdom? ;) Can’t thank you enough for doing this vid. It’ll come in handy for sure!

[@timrayburn2461]

Great explanation and video.

[@UnityMotorSportsGarage]

Thanks for the kind words...

[@daleapostal7896]

Another excellent video! mr. Vizard & mr. Wood do such a good , interesting presentation! Could you use the ported spark port for water injection to address detonation? Thanks to both of you;

[@UnityMotorSportsGarage]

Thank you Dale! I wouldn't use the ported vacuum port for water injection.. distribution would be a issue.. You could run a carb spacer and drill and tap it for a nozzle to inject into the intake directly below the carb... I've never ran water/meth injection on a NA setup, but I do know that it could pay off in heavy load situations .. Andy

[@terrysibley9636]

Good morning. Question, I'm looking for tuning advice, info,and general understanding of tuning for elevation.

[@UnityMotorSportsGarage]

What are you working on? Andy

[@terrysibley9636]

@@UnityMotorSportsGarage thanks for hitting me back. Happy labor day weekend. And yes we are happy laboring out here in az

[@terrysibley9636]

@@UnityMotorSportsGarage hello thank you. Live your guys work. 311 ci. Sbf. New eagle crank,rods. Kb hyper. Pistons .200 solid dome. No Nitrous. Solid roller lunati. Smallest grind short duration voodoo, with 110/106 with .594 intake, .604 exhaust. I live at 5000 ft. A subject not covered much. Its different now because I'm not in Houston anymore where raceway park is 50 ft above sea level.lol. considering a pro max aluminum. Heads 58 cc. Should put me between 10.7. And 11.1 depending on hesd gasket requirements. Heres my dilemma, 180cc int. 190cc, I mean 200cc. Just don't know. Weekends holidays and the occasional 120 mile work trip. Not a daily driver. Fun truck. 5 speed with as is a 3.73 rear. But then there's the elevation. So thanks for any all help or suggestions would be greatly appreciated. Carb sizing,single plane dual plane, ??. And its all going back into a 2000 ford ranger 2wd. Have a great weekend. Frkm off the grid az.

[@bobhemphut4011]

After a couple years of running ported vacuum mb was getting 20 mpg cruising. I switched over to manifold vacuum on my mildly built 355 sbc after seeing a few videos explaining it. I have a world class t5 manual and professionally tuned quadrajet in an 84 trans am. I get damn near 30 mpg cruising on the highways.

[@timothy7927]

How do you set timing after driving and checking with vacuum gage and pump

[@Jimmyk63]

Thank you for your insitghts and video 🙂❤👍

[@hoost3056]

Man, you know one of the OG geniuses of the game! Still would love to get a 128 Theory cam from him👍

[@UnityMotorSportsGarage]

David is a genius.. back in the Dyno testing we did with "Ole Blue" we had Crane grind many different grinds and the grind that David's program said would make the most power... Did by like 20hp and 20lbft of torque

[@autonomous_collective]

Great great video! Thank you!

[@georgespain6121]

At any point will manifold advance make a stock engine stumble where ported wouldn’t?

[@chevroletbelair1]

Can you and you're buddy David make some step by step vids on how to adjust a Holley carb and ignition timing(included vacuum advance?)

[@51farmalla]

My 1955 GM manual and 1960 Ford manual both use only ported. Except the Ford Load a Matic which use venturi and manifold with a spark control valve to control the two. I got more manuals to check however. All my engine engineering books also say ported.

[@kurtzimmerman1637]

another good video andy! keep up the good work!

[@UnityMotorSportsGarage]

Thanks again! Andy

[@kishorejayaswal1500]

Gonna try these adjustment! 1967 Camaro w/327, Edlebrock 4bc, vacuum advance.

[@jonathan-emilypowell1962]

David is the man with the plan!

[@jesse.jsmall0652]

I have a 1982 Z28 Camaro sbc 355 with a th350 transmission and a vacuum secondary Holley 750 I believe… Help me out here what should I do to make a bit more snappy and reliable at lower throttle still running ported makes good ish manifold vacuum and 55psi of oil pressure any suggestions appreciated… Thanks

[@sheldonbromen2603]

i have a 94 mustang with a 351W i swapped in and i have been having trouble tuning it was looking at different carb tuning videos and found your channel i love it so far i have a procomp pro billet knock off dizzy with no VA and want to buy one with an advance bad! so far i have managed to squeeze about 25 mpg out of it when cruising 55 to 65 but i know i can do more with a properly tuned carb and properly curved dizzy. i haven't found anyone in the state that does this type of tuning anymore so i am forced to learn myself. i would love to send you a more detailed email and explain all of it to pick your brain but i am sure you're a busy man!

[@UnityMotorSportsGarage]

Sheldon, Thanks for the kind words... If you are on facebook just hit me up in messenger or my email is [e-mail] Thanks for Watching and please subscribe as I have more good stuff coming! Andy

[@leelandcollins2146]

What should the vac advance setting be at while doing all this? The adjustment screw I mean.

[@UnityMotorSportsGarage]

The adjustment screw should be turned all the way out so you can get the full range of the Vacuum pot. hope this helps, Andy

[@ajforms4818]

Here's my corroborating experience; I have a manual-trans 68 Barracuda, with an 11/1 Eddy-headed 367, that, in the very early 2000's, my son and I cruised down in, to the CarCraft Nationals in Shakopea Mn. I drove that combo down there with an A833od with a GearVendor behind it and with 3.55s for a Final-Drive ratio of 1.97, and 75=1850rpm. She was topped by an Airgap and modified 600Vsec, with fresh-air, and she always burned 87E10 for it's whole life. I have run three different cams in that engine since 1999, and the smallest one was a Hughes 223/230/110 @.050... which is what was in it on this day. I was able to get the total advance from all sources, up to 54* using a maxed-out Vacuum Advance Can, plus a stand-alone, dial-back, timing retard box, and she was still accepting more. The Fuel economy exploded to a number nobody believes, and without fail, I am called a liar....... So I won't divulge the number here except to say that it was in the arena where injected Ecotecs run. When we got to our destination; I bolted the 750DP back on, dialed the advance back to normal, and we gave her hell, fuel economy be damned, lol. After the weekend was over, we swapped the 1850 back on, tanked up, and headed home, about 10 hours to the North. With my 18year old son, we made a fine fine memory, that we still sometimes talk about. ---------------------------------------------------- I did pretty much what you guys did, but from a different angle. I installed both a tach and a vacuum gauge, then plotted BOTH my mechanical advance curve and my V-can curve. After that I always knew, be consulting the curves, how much timing the engine was getting at any rpm or load. But my cruise vacuum was pretty steady, at 1850 rpm and changing the advance never produced much of a change in manifold vacuum. So what I did instead, was fabricate an adjustable throttle stop (which I could blow-thru if I needed to, but it was consistent), which I then set, in a way to allow the car to just achieve 65mph. Then after cruising there for a time to stabilize it, I would add about 3* timing by my dial-back, and note the increase in speed. Then, the next time out on the same route, I would reset the throttle stop back to 65, then repeat the timing addition, and note the increase. And so it went for several weeks until one day, no further speed increase was noted. Then, that was repeated one more time on a following occasion, to verify.. And that is how I came to find 60 degrees seemed to be the ceiling. I arbitrarily reduced that to 54* degrees , so the dial-back could give me minus 9* at idle. As for the -9*; that dropped my initial timing from 14* to 6*, which reduced the idle power enough so that the car would pull itself thru the parking lot, parading at 500rpm=3.5 mph, without bucking, and without any need to toe the clutch, or touch the gas-pedal. I deemed that more important than the lost fuel-economy at hiway speeds, which was not as big a part of the car's life. Yeah, and that 223* cam, at 500rpm had a nice lil cadence. I found out later, that the little Hughes 223, had an advertised of 270/276@008 tappet. sweet. I have fond memories of that cam.

[@silcoxone]

Im gonna have to watch this a few times!!!! 67 Bronco, 289... Very small cam... Like 250ish, cam range is 1000 to 5500. Edelbrock carb. I have my Vacuum advance on ported... I've always had to shift down to pull small hills because engine doesn't wanna pull unless I make it pull. I have 20hgm vacuum at idle. I gotta go to Part 2!!!!!!!!

[@UnityMotorSportsGarage]

Thanks for Watching! Please Subscribe and if you have any questions just email me at [e-mail] Andy

[@greghaig2764]

I had David for a teacher way back when great guy ☺️

[@UnityMotorSportsGarage]

That is awesome! He has been a great teacher to me as well... Andy

[@CarveLife]

If you suck on the vacuum advance canister should it move pretty easily? Mine is extremely hard to move even with my finger on the arm

[@mikeburnett7028]

Found your timing video finally. Can you do a detailed video of how you use a vacuum gauge along with the hand held vacuum pump to set total timing? Frankly, most of this is over my head unless I can see it being done. My bb Chevy gets hot at idle and I think this process will help alleviate my issues. Please help me make my engine more efficient. Thank you 🙏

[@Denver1976Man]

I know this was 4 yeats ago but I have a question. You atre talikng of high performance engines. I am wanting to get the most out of my old AMC 258 straight 6. I put a crown 2BBl and an HEI. But def no cruise,,,kik

[@ghtrcp7554]

Great video.. can i use vacuum advance on blown 383 with msd 6al-2 programmable ignition box?(7 psi, 8.7:1) i am planing to 22 initial, 34 total..Would it cause detonation? Ty very much..

[@UnityMotorSportsGarage]

Yes you can.. as long your supercharger has a bypass valve and sees vacuum at cruise it will work. It won't cause any harm because once you begin build boost, the vacuum advance is taken out of play! Thanks for watching Andy

[@ghtrcp7554]

@@UnityMotorSportsGarage Thank you very much. 👍My big question; When before the first start with my locked distributor, crank will be at 34* degrees before firing and the distributor rotor will point to #1 cylinder.. Am I right? Or am I going to do first start like any other unlocked distributor at TDS (0* at crank) at compreesion stroke for #1 cylinder? I am lost here..Thank you very much.. ❤

[@nursecuenca]

I new to your channel and classic cars. On 350 chevy engine with edelbrock carburetor there's 2 ports. 1 for vaccum to distributor and the other seems to go towards transmission. Does the carburetor need 2 hoses or just 1 hose connected to carburetor?

[@garykish8951]

David Vizzard is one of the last of the legends. It's worth looking up everything he's written about high performance.

[@UnityMotorSportsGarage]

DV is a brilliant mind that is forsure! I'm very fortunate to be able to call him a great friend.. Andy

[@trailerparkcryptoking5213]

Andy what kind of distributor do you run on your truck?

[@CharlieBrown-pb9xn]

I heard from Warren Engines that at high rpm that advance can go way up. Whats your take. Ive been using bout 36 total and bout shure im losing at 6500rpm

[@browserrr1]

@Charlie Brown, I don't know what advance can go way up but it won't be vacuum. running at high rpm means around wot, meaning little to no underpressure in the manifold so no vacuum advance.

[@357fairmont]

Why does msd tell you in their instructions to install the vacuum advance hose to ported vacuum?

[@gerardogonzalez1312]

So if I swap my vac advance to manifold do I set my initial timing with vac advance hooked up? And also do I put a tee so I can hook my vac gauge and adjust my idle mixture to highest vacuum while the vac advance is connected?

[@Sblackb2]

Followed your steps and it runs great when the engine is warmed up. When it is cold it pings. I have played with backing it off but then it runs poor. Sbc 350 with edelbrock 1906. Do you have advice?

[@4eyefoxbodyfanclub625]

My foxbody mustang has a locked out MSD distributor and is terrible on gas, why do some race engines run with locked out timing? Is there any advantage to it? Ive been wanting to unlock it and run off vacuum advance to see what happens but I leave it alone cause the engine was built at a pro shop and Im sure they tuned and built it that way for a reason. It currently runs the 1/4 mile at 12.3 seconds@112mph.

[@UnityMotorSportsGarage]

Thanks for Watching and bringing up a great point... It is merely a matter of convenience... If you are running a crank trigger and using the distributor for spark delivery I can accept it... But for ANY engine driven on the street taking time to give the proper spark Advance throughout the RPM range will reward you with big increases in mileage and depending on your combo you may pick up torque down low as well! People will eliminate something if they don't completely understand it... My truck weighs in at over 4000lbs makes 600hp (flywheel HP) and runs 7.3x's in the 1/8th which is mid 11's in the 1/4 and gets over 16mpg... With a Tunnel Ram and two Holley Center Squirter carbs Andy

[@AK-wx2oc]

I’m confused...So I am currently running a mech only advance dizzy on a mildly built street 289 and will be replacing with a vacuum advance unit soon along with a good afr gauge...16 degrees base with a total of 36 degrees all in about 2,700 rpm. I’ve got 11 inches vacuum at idle and am right at the cusp of needing to drill throttle plates to get the idle but will wait until I get the new dizzy and afr...So run manifold vacuum and not ported and go through David’s process- is that correct??? And set base timing with manifold vacuum connected??

[@armandomendoza3167]

One of things we all haved done is thinking inside the box. I had to experiment with my 95 chevy 350 1/2 ton truck. The base timing is 0°from the service manual. I have changed it to 6°advance. After realizing that the 92 Camaro 350 TPI, 91 Corvette 350 TP and 95 Cadillac Fleetwood 350 TBI had a set timing of 6°. After driving it with a 6°base timing advance. Totaling between 26°total advance. I was surprised to to get an additional 5mpg to the gallon. Before it was 12 city and 15 hwy with a 13.2 +- avarage. Now I'm getting the average of 19.25 mpg. I'm assuming 15 city and 24 hwy. And the truck weighs 5000+ lbs. I had to get out of the box and try it for myself. The engine liked the extra 6°. Since I have to take a different approach since it has a Tuned Port Injection with a computer advance distributor. I have to give it baby steps. And find out where is the to motor and computer is the happiest in harmony. Thanks for this video.

[@matthewmiller2268]

That's wisdom and knowledge that needs to be shared

[@armandomendoza3167]

I will update the results at 70 mph to see if it is better or the same. Right now my father has my truck. And he is in Mexico. He was towing a small 8ft x 4ft trailer. With the back of the truck bed fully loaded. So I will get as much information as possible. To see where it stands on economy in different scenarios.

[@roccoloops]

Really great video - loved the level of detail on one of the most mis-understood concepts going around (especially with modified engines). I experiment with manifold vs ported on my modified engine using the standard dizzy but had issues because with the compression / cam combo I got pre-ignition on light throttle. Left it unhooked for years and just got hotter engine bay temperatures and not as snappy throttle response.... After watching this I've got a new distributor on order and will be performing the tune process outlined to get it 100% dialed in. Appreciate the advice and I'm very keen to get cracking once my new unit arrives :)

[@oydina-leebanks534]

when i set my idle at 14-15 AFR i get a lot rougher idle. How do you set up your idle that lean? I have a 496 BBC 230 236 cam

[@joe-hp4nk]

I enjoyed this video, R.I.P. Andy

[@UnityMotorSportsGarage]

R.I.P, Joe I'm still around! Lol Thanks for watching Andy

[@joe-hp4nk]

@@UnityMotorSportsGarage Sorry, wrong Andy. Carry on.

[@scotty162]

I am from New Zealand, I detect a kiwi/aussie accent in David. Where is he from? PS: I used his book "How to rebuild a small block chevy) when i was 19, in 1984, to rebuild a 350, which i went on to put 40,000 miles on, Thanks Dave.

[@UnityMotorSportsGarage]

You are partially correct! He is from England but his Mom moved to Australia and he has spent a great amount of time down under with her... I will let him know! Thanks for Watching Andy

[@ericuncapher9922]

Thank you guys!

[@thechillhacker]

Idle running cooler is awesome, but when I switched my wagon's can over to manifold and retimed it, the whole engine ran about 5-10 degrees cooler on the gauge, while having more power where it counts, and a smoother idle. My fans barely even kicked on, even while climbing the tallest highway peaks in new england at, let's say, vigorous highway speeds, passing one car after another with ease. Winning all the way around. I don't see myself going back, but to be scientific, I'll probably try both methods on the next few engines I build or restore, and see what each one says. My FE390 also of course, prefers manifold. Only time and more experience will tell, but so far I'm a believer. The science is sound, and if the Vizard Wizard says it is so, it is almost certainly so. Testing it out on my 425 in its dynamic 88 convertible will be "boatloads" of fun. Thanks!

[@1crazypj]

That was really interesting. I have very little experience of vacuum advance as it's very rare on motorcycles (I've only ever seen one unit in 50+years on a bikes)

[@eslim95023]

I have a question 🙋‍♂️ so when I set my initial timing I warm up the engine to operating temperature do I plug my vacuum advance first before hooking it up to manifold vacuum or do I set the timing with the distributor connected to manifold vacuum right off the bat ?

[@rf4215]

set timing with vacuum on manifold plugged

[@TaekwondoFitForLife]

Thank you, thank you, thank you Sir! I’m following you, and really appreciate your clarity and The best proven better than “opinion” on vacuum advance sources which helped me so much! My engine 383 in my 1863 Chevy C10 with manual 4 speed 3:73 ratio rear runs cooler because of using “manifold vacuum source”. “David Visard” I follow him as well, knew “at the time of decision” being epa driven primarily fo the swap during the time of manufacture decisions..as Mr. Visard is equating.. So cool to have “understanding” of the reasoning for the old differences of “opinion”.. Ha ha, love-it, not what “you” want but what the “engine wants”… “Thanks for my education and decision to go with the actually higher value= manifold vacuum.” I run cooler at lights with a healthy Howard’s cam, used to go up fast in temp, now plateau……❤

[@ironguts1097]

Great channel! Thank you for your content. I was hoping you could get in a Q for DV for me! I want to know what happens when you put in a really long duration, tight LSA camshaft (300+ 106) and big tall intake on a poor engine, such as a good wrench 350. I can’t find the answers anywhere! I have searched for years and have read every DV book I can get ahold of. Even the A series book! If an A series can run a 300+ camshaft, why can’t a good wrench 350 run one in a very light car? (Under 2000lbs)?? Thank you!

[@cuzz63]

I learned something from this video. I always thought total timing was the maximum timing you could get with the mechanical and the vacuum only increased timing from the initial to whatever the can allowed somewhere below the total. I didnt get that the vacuum advance would increase it above the mechanical..