for you guys on manifold vaccum on advance dizzy

[barnett468 418]

well its obvious to me from his statements that he simply doesn't understand what he is saying and he sounds like he is simply repeating what the other person wrote in the other link posted on your thread which is factually partially right and partially wrong, and since both are partially wrong and some people that read it or see the video don't know enough to be able to tell which parts are right and which parts are wrong, it's not helpful, and doing what is suggested can reduce performance in some cases and possibly cause some type of engine damage in other cases.

 

as i mentioned, not all engines are the same, some have bigger cams or higher compression than others etc., and some have different gearing, and all these things factor into a particular engines timing requirement . . also the blanket statement that engines run lean at idle and cruise is simply ludicrous . . i can make any engine run lean or "ideal" or rich, at both idle and cruise and so can you . . just turn your fuel mix screws out 4 turns and stuff some 95 size main jets in your carb and i guarantee you that it will be both rich at idle and cruise.

 

in general terms, when an engine is jetted properly, it never runs lean or rich, it simply runs at the "ideal" ratio which is not perfectly achievable on a carbureted, non computer controlled engine.

 

ignition timing is a bit like jetting and beer. too little OR too much is bad, and one size actually does NOT fit all, lol.

.

Edited October 20, 2014 by barnett468

[barnett468 418]

Tada! There it is again!:no:

but...but...the author claimed he is a rocket scientist. Plus, it's on the internet so it must be true.

[barnett468 418]

Ok, here’s just part of what the rocket scientist (sorry, purported GM engineer) said, which is wrong, incorrect, inaccurate or whatever.

 

 

“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… …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.”

 

There were ABSOLUTELY NO EMISSIONS REQUIREMENTS in 1956 when Chevy used PORTED vacuum (not manifold vacuum as the “engineer” states or implies etc..), and in fact, they used what is called a road draft tube instead of a pcv valve to vent the crankcase. A road draft tube is nothing more than an open tube that vents the crankcase onto…wait for it….THE ROAD.

 

I may be very mistaken but I personally do not think that this is the least bit environmentally friendly or emission reduction related and I’m guessing that the guy in the car that is behind one of these cars and which is getting splattered from gas contaminated oil that is spewing out if this tube that is connected to an old worn out engine that has excessive blowby, thinks it is either.

 

Also, 40 years BEFORE federal automotive emissions standards would be around 1926. Well the 1926 Ford didn’t even have a vacuum advance. It had a mechanical one that was operated mechanically by a lever mounted on the steering wheel!

 

 

 

“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).”

 

One should try setting their timing to 2 degrees atdc then connecting their vacuum advance to manifold vacuum and see if their car will even start.

 

The ignition timing of a 1956 Chevy V8 is 4 degrees btdc and since there were no emissions standards at that time, Chevy could have put it wherever they wanted to, so why did they decide to use only 4?

 

 

 

“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.”

 

Try running 22 degrees of idle timing from manifold vacuum on a 10:1 or higher compression engine that has a multi fire ignition box like an MSD 6 series.

 

 

Auto and industrial emissions history

 

http://www.autolife.umd.umich.edu/Environment/E_Overview/E_Overview4.htm

 

 

Look at the photos below. The very common 1956 Chevy V8 distributor vacuum advance was obviously connected to ported vacuum.

 

 

...................................................1956 chevy factory 2 barrel v8 carb.

 

......................................................

 

.

 

1956 chevy factory vacuum advance routing.

 

.

Edited October 20, 2014 by barnett468

[j69302 11]

First of all, idle mixtures are not lean. Idle mixtures are typically rich, because rich settings run cooler. Tune a idle system with a vacuum & AFR gauge for highest vacuum (which just so happens to also be highest efficiency), and you will see the air fuel ration is 12-13 and not "lean" which would be 14+

 

Also, while driving, is isn't about a lean mixture vs a rich mixture. It's about how much air and fuel are in a cylinder, and how much time there is for it to fully burn. The more air and fuel in the cylinder, the more time you need for it to burn, there fore the more advance you need.

 

At idle, your throttle valves are close as much as they will ever be, reducing the volume of air you engine takes in, and your volumetric efficient is not much at all. The cylinders, are actually quite empty as far as the amount of air and fuel, there fore less timing is needed simply for the fact that there is not much fuel/air to burn.

 

Now at cruise, your engine speed is low(ish), your throttle valves are probably somewhere between 20-33% open, you engine is actually taking it quite a bit of air relative to its speed, and there fore NEEDS more time to burn.

 

However because of the moderate "load" on the engine, your "manifold vacuum" is low - especially if you have a bigger cam, as a result, your vacuum advanced, hooked to a manifold source, isn't doing much of anything at all.

 

Now, if it is hooked to ported source, you will get a lot of vacuum on your vac advance, and you will be giving the mixture more time to burn.

 

At full throttle, neither manifold or vacuum is really doing very much.

 

Just cause somebody claims to be this or that on the internet, doesn't do anything for me. I've spent many hours tuning my carb and distributor with an air fuel meter and vacuum gauges, actually seeing what is going on.

 

Everyone knows this: Manifold vacuum is strong at idle, weaker are cruise, and virtually non existent at full power. Vacuum is what makes the system advance.

 

However, knowing vacuum goes away as load increase(where the advance is needed), people still hook it up to a manifold source. You're only giving yourself less advance, and when you push the throttle a little bit to speed up, your manifold vacuum drops ALOT for that time being, resulting in retarded timing, but ported, would actually go up, giving you more advance.

 

Also, ported vacuum is not affected so much by cam size. So a big cam won't change your ported much. It will remain more consistent.

Edited October 20, 2014 by j69302

[barnett468 418]

Hello Juit;

 

As I mentioned, ported vacuum is exactly the same as manifold vacuum after the throttle is partially open, here's proof. One can also easily do this test for themselves if they have two vacuum gauges.

 

The time from just past 15 to just past 16 is steady throttle with the pedal depressed around 8% of the way with slightly increasing load on the vehicle. This closely resembles cruise mode at around 30 mph. Notice that both the ported and manifold vacuum are virtually the same here also.

 

 

.......

.

Edited October 20, 2014 by barnett468

[SWPruett 83]

Excellent stuff gentlemen!

 

Of course, until this is published on the Corvette forum, by somebody with a retired GM Engineer signature, it can't possibly be believed. Pretty pictures though!

 

But seriously, this is the kind of thing that is genuinely helpful! Much appreciated and I hope the O.P. finds it so as well.

[Max Power 74]

Hello Juit;

 

As I mentioned, ported vacuum is exactly the same as manifold vacuum after the throttle is partially open, here's proof. One can also easily do this test for themselves if they have two vacuum gauges.

 

 

Well, with big cams, usually the throttle is partially open at idle anyway, so ported in essence becomes manifold, or at least partial manifold. Most big cams get you into the transfer slots at idle. Part of the challenge, I guess. Also, you stated earlier that people with big cams run manifold vacuum, and there are some dangers there, especially with automatic transmissions. When you drop your car into gear, manifold vacuum drops, in essence pulling timing away from a non-moving car. This leads to stalling and drivability problems.

 

Final observation on this whole subject, if you are using manifold instead of ported, remember that your factory dizzy is curved for ported. Hard to get a car to run perfectly using a vacuum source that the dizzy was not calibrated for, regardless of vacuum source.

 

Both can work, but people tend to hybrid it, leading to problems.

[barnett468 418]

the factory dizzy is also set for emissions, and in many cases has less mechanical advance than an engine can tolerate but they are easily curved.

 

as far as me saying anything about running manifold vac with a big cam, that is not what i am suggesting. my others comments should hopefully make that clear and i apologize if it sounded otherwise.

 

one can figure out what their engine likes by using as much of a scientific approach as possible and run it, the engine itself will determine or tell us what it wants, its pretty simple.

 

as far as big cams needing to have the throttle partially open to idle causing the ported vac circuit to be operational, this is very easily cured in most typical street car apps by either drilling holes in the front butterflies and/or opening the secondaries slightly etc.. in some cases the idle feed restrictors might need to be enlarged but this is fairly uncommon in my experience. i have done the other things way more times than i can count but prefer to leave the secondary plate in the "stock" position if possible.

 

in most cases where it is not possible to get the throttle plate closed enough to shut vacuum off to the ported vac port, these cams are bigger than what i would consider daily driver street builds and would consider them to be more of a drag race cam that someone is running on the street and if someone chooses to run a drag race cam on the street they can expect that their ported vac will be operational at idle. they should also not be overly concerned about running a vacuum adv dist anyway imo.

 

also the more advance one can run at idle, the more closed the throttle plates can be. i always set the idle timing and fuel mix screws to the optimum level before drilling anything.

.

Edited October 20, 2014 by barnett468

[barnett468 418]

Excellent stuff gentlemen!

 

Of course, until this is published on the Corvette forum, by somebody with a retired GM Engineer signature, it can't possibly be believed. Pretty pictures though!

 

LMAO!

 

i wonder what they would do if if "someone" did that, lol.

 

they could search from now till kingdom come and may never find a car that used manifold vac from the factory other than possibly the fuel injected vettes.

 

Hey, i see the words boss 302 in your sig. do you lurk on the boss registry and/or know mark with the red 70 in fallbrook/san diego?

Edited October 20, 2014 by barnett468

[DocWok 30]

Hi juit,

 

Guess you'll have to experiment a bit for yourself and see what works best for you.

 

Remember on a forum, despite their assertions, no matter how smart the resident genius poster may sound, he can still be wrong......

 

[SWPruett 83]

LMAO!

 

i wonder what they would do if if "someone" did that, lol.

 

they could search from now till kingdom come and may never find a car that used manifold vac from the factory other than possibly the fuel injected vettes.

 

Hey, i see the words boss 302 in your sig. do you lurk on the boss registry and/or know mark with the red 70 in fallbrook/san diego?

 

I think we should write a decoy article just for the 'vette forum just to "f" with 'em. They hate that! :laugh:

 

I have been a long-time member of the Boss 302 forum but don't play much over there. More of a stocker crowd and that ain't me! However, I do recognize the Mark/Red Boss/Fallbrook, CA owner you describe. A regular contributor as I recall and a very nice Boss by all I have seen posted.

[barnett468 418]

I think we should write a decoy article just for the 'vette forum just to "f" with 'em. They hate that! :laugh:

 

I have been a long-time member of the Boss 302 forum but don't play much over there. More of a stocker crowd and that ain't me! However, I do recognize the Mark/Red Boss/Fallbrook, CA owner you describe. A regular contributor as I recall and a very nice Boss by all I have seen posted.

lol i like the way you think however in reality it would really be cruel and heartless of of us to destroy some...ok all of the vette guys and some other chevy owners beliefs . with actual facts. . i have actually had a bunch of 50 and 60s vettes bel airs and chevells as well as fords and mopars and i actually restore cars for a living so this is how i knew that what he said about cars ufrom the factory having manifold vac was questionable and after seeing that um aticle appear i decided to simply see if i could find any that did that because i had never seen it and like to learn new things because i know that i dont know it all and i gave the author the benefit of the doubt so i spent a lot of time looking for this elusive set up and other than the possibility of the fuelie vette i mentioned i could not find any . now this certainly does not mean that none of them were set up this way but in my experience i have never seen it . . oh by the way i would really hate to tell them that the vacuum graph i posted was actually made by a gm guy with a gm car.. . . yes marks car is or was killer but he drives it a bit so its getting some dust and patina on it .. . he actually restored the orange boss race car for the old trans am driver too.. . ofbeb

Edited October 21, 2014 by barnett468

[juit 34]

Nice reading

[DocWok 30]

Hi juit,

 

Here's a very interesting article from a fellow Mustang owner over on the VMF forum:

 

 

Join Date: Oct 2009

Posts: 1,314

 

 

Vacuum advance vs mechanical only - Proved it...

After years of running MSD dizzy without vacuum advance then going to a Ford dizzys with disconnected vacuum advance because I couldn't get them to run right, I finally brute forced through this one with impressive results.

 

I have always run 36 degrees full mechanical advance from a dyno run on an old motor. I could never get vacuum advances to work on my motor no matter what carb, port or dizzy I tried. A recent thread on a disappointing dyno run got off track on vacuum advance topics. I also recently did a MPG calc and got 10 MPG on an easy run to work and back 75 mi, thats $28 bucks for a round trip. That got me incentivized to finally solve the vacuum advance riddle on my car.

 

I found several articles and posts that told me a trick I did not know; limiting the amount of vacuum advance by using an Allen wrench inserted into the vacuum canister where the vacuum tube inserts. So I opened up an old vacuum canister to see how it worked. The vacuum pulls toward the vacuum tube. If you insert an Allen wrench and "Unscrew" it - it unscrews a large plate toward the vacuum tube connector which limits the amount of travel on the canister.

 

With my Performer RPM flat tappet cam, I get about 10 to 11 inches vacuum which was pulling 20 degrees of advance on a stock cannister when I put the vacuum line on. Car would die an ugly death at idle or run extremely poorly popping and farting if I tried to force it. I started at 15 degrees difference between putting the vacuum tube on and removing it. I found I had to keep dialing back till most of the popping in the mufflers off throttle was gone. It only pops when you drive it and go off throttle. Won't do it in the driveway. I finally dialed it back to around 5 to 7 degrees at idle and the difference was very interesting, changing the personality of the car.

 

Now my throttle response is amazingly quick at any throttle setting EXCEPT wide open throttle (WOT). NOTE: My car is no faster than it was without the vacuum advance hooked up on a floored WOT pull through the gears.

 

But for normal driving, it has a whole new personality - FEELS like it has a lot more horsepower. Actually, it feels like I made a major leverage change on the throttle where I only have to barely touch it now to get the thump I used to have to give 1/4 throttle.

 

The other thing I noticed is that my temp idling through the neighborhood and idling dropped noticeably.

 

All of this is consistent with what the literature told me I would experience. BTW, I hooked it up to direct manifold vacuum as all the articles said to do for anything but a full up smog car from the dark years which used the ported vacuum above the throttle plate.

 

Hope this helps someone else, it only took me 12 years to solve this mystery. I know there is more messing around to do to get things dialed in but its definitely on the right track.

Last edited by dobrostang; 06-18-2011 at 11:25 PM.

[barnett468 418]

Unfortunately, the problem with his comments is that he doesn't explain in a clear, concise, chronological way, exactly what he did.

 

He never says whether he had it connected to ported or manifold vac in the first place.

 

He never says whether he tested it on both ports after changing the vacuum chamber setting after he finally realized that some of them are adjustable including his.

 

He therefore leaves the reader to make assumptions if they choose to that can lead to an incorrect conclusion.

 

Their are proper ways to perform and document "scientific" testing that leads to reasonable, understandable, conclusions, and repeatable results. Unfortunately, he did not do that.

 

He also said quote, "I finally dialed it back to around 5 to 7 degrees at idle...". Ok, well it sounds to me like his timing at idle was 7 degrees after he adjusted the can. Well, since stock is 6 degrees, if in fact he only had 7 at idle, it sounds like he wasn't getting much advance if any from the vac can.

 

He also did not say if the vacuum advance even added any timing after he got done reducing the timing it provided by adjusting the can.

 

You can adjust the cans so they will not provide any additional timing, and since he did not clearly, specifically, state if he even checked to see if it did, his comments are unfortunately not useful in any way.

 

What was his timing at idle from both ported and manifold vac before and after the can adjustment?

 

What was his total timing before and after?

 

What rpm did it reach max/total timing?

 

Without this info, it is impossible to replicate exactly what he did by his comments and know exactly what timing he ended up with.

 

All we really know is that his idle timing MAY have been 7 deg btdc after he was finished, and his car went fast after he did whatever it is he did, ok...great.

 

 

 

“After years of running MSD dizzy without vacuum advance then going to a Ford dizzys with disconnected vacuum advance because I couldn't get them to run right… I could never get vacuum advances to work on my motor no matter what carb, port or dizzy I tried. I found several articles and posts that told me a trick I did not know; limiting the amount of vacuum advance by using an Allen wrench inserted into the vacuum canister where the vacuum tube inserts.”

 

Ok, so he admits that he has no idea what he is doing or how a vac adv can works.

 

 

 

“So I opened up an old vacuum canister to see how it worked. The vacuum pulls toward the vacuum tube. If you insert an Allen wrench and "Unscrew" it - it unscrews a large plate toward the vacuum tube connector which limits the amount of travel on the canister.”

 

Turning the screw out also affects when the can is activated. The farther out the screw is, the more vacuum it takes to initiate movement but he made no mention of that so my guess is that he never figuered that part out.

 

 

 

“With my Performer RPM flat tappet cam, I get about 10 to 11 inches vacuum which was pulling 20 degrees of advance on a stock cannister when I put the vacuum line on.”

 

He does not say if he connected his vacuum line to ported or manifold. It “sounds” to me like he connected it to ported, however, as Max Power mentioned earlier, many people that have big cams simply open their throttle plates until their car idles, which in many cases causes the ported vacuum to have vacuum, so it is also entirely possible that this is exactly what this person did. There is no proof either way, so this particular info is not helpful.

 

Well, with big cams, usually the throttle is partially open at idle anyway, so ported in essence becomes manifold, or at least partial manifold. Most big cams get you into the transfer slots at idle. Part of the challenge, I guess. Also, you stated earlier that people with big cams run manifold vacuum, and there are some dangers there, especially with automatic transmissions. When you drop your car into gear, manifold vacuum drops, in essence pulling timing away from a non-moving car. This leads to stalling and drivability problems.

 

 

 

"Vacuum advance vs mechanical only - Proved it..."

 

Although I do appreciate his effort and enthusiasm, the only thing I think he really "proved", is that he is not an experienced "tester" because I can't make heads or tails of EXACTLY what it is he did and is saying.

.

Edited October 21, 2014 by barnett468

[barnett468 418]

This is one of the anomalies that can occasionally occur when using ported vacuum. I have in fact experienced this on a few occasions but the condition was minor and I took corrective measures to eliminate it.

 

"Vacuum delay valves

 

The vacuum signal from the carburetor spark port can momentarily spike when the throttle plates begin to move. Generally, this is more likely to occur when the throttle plates are closer to being closed (at or near idle).

 

To prevent pinging problems caused by such a vacuum signal spike, Ford used vacuum delay valves inline between the carburetor spark port and the vacuum advance canister on many engines. The vacuum delay valve is just a metered orifice that slows down the transmission of the vacuum signal, effectively buffering out any spikes in the signal.

 

You may need a vacuum delay valve if your engine has persistent problems with off-idle pinging, or momentary pinging at part-throttle acceleration, even when vacuum advance sensitivity is reduced to its minimum."

.

Edited October 21, 2014 by barnett468

[barnett468 418]

.

The following post is from a CHEVY guy. The person named Cliff Ruggles that he is referring to is one of the most well known and respected GM carb authorities and rebuilders.

 

 

"After reading and reading the debates and explanations of manifold versus ported vacuum to the vacuum advance unit, i have to say my stock 350 performs better using ported vacuum.

 

It wasn't until recently reading Cliff Ruggles book "How to rebuild and modify Rochester Quadrajet Carburetors" that he gives his two cents, on page 49, about using either ported or manifold vaccum and pretty much leaves it up to the individual to decide.

 

Interesting that he makes mention of two of the major points of manifold vacuum that the car runs cooler and gets better gas mileage that these are applicable if the car were running, in both cases, at idle constantly! whoa!

 

He also mentions that there is no substantial proof that manifold vacuum does what "they say" and that he has tested both in hundreds of cars including his own and it seems that leans toward ported vacuum!

 

From my understanding in car that needs help with idle, like a big cam or even one that spends a lot of time in commute traffic (idling), for example, and has problems with running hot, manifold vacuum would be probably a better bet, but i have to say for throttle response through the different rpms my stock 350 runs better with ported vacuum.

 

It is interesting that on this learning about my engine and how it works that there are all kinds of scenarios and setups that effect things that no one way of doing things is THE way.

 

For now ported vacuum is working for me.

 

http://www.chevelles.com/forums/showthread.php?t=375251"

.

Edited October 21, 2014 by barnett468

[Max Power 74]

 

You can adjust the cans so they will not provide any additional timing, and since he did not clearly, specifically, state if he even checked to see if it did, his comments are unfortunately not useful in any way.

 

 

It's useful in one way. Many people did not know that vacuum advances were adjustable. After that, even if he answered your specific questions, his setup is different than most others here, so "useful" would be selective regardless. What works for him may or may not work for others.

[barnett468 418]

It's useful in one way. Many people did not know that vacuum advances were adjustable.

You are correct, my apologies for overlooking this...I think. :sorcerer:

 

 

After that, even if he answered your specific questions, his setup is different than most others here, so "useful" would be selective regardless. What works for him may or may not work for others.

Yup, xlnt point, so as has been mentioned, simply do a proper comparison and see what is best for ones particular set up, but as you and some others well know, by no means should one simply remove their vacuum from ported and shove it onto their manifold vac and assume its better just because they read it on the internet [and because it was signed by someone who claims they were a GM engineer] like many people do. This is one of the most incredibly irresponsible suggestions I have ever heard regarding timing.

.

Edited October 21, 2014 by barnett468

[MAD IN NC 21]

Excellent stuff gentlemen!

 

Of course, until this is published on the Corvette forum, by somebody with a retired GM Engineer signature, it can't possibly be believed. Pretty pictures though!

 

But seriously, this is the kind of thing that is genuinely helpful! Much appreciated and I hope the O.P. finds it so as well.

 

Now that is hilarious! I've restored a 65 Vert Vette over the past few years and have fought and fought overheating till I was crazy! and he cvet forum always said timing, timing, Dewitt radiator and timing ROFL

 

 

I have the article I believe you refer to.. a good one but is to big to post (2.1Mb)