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Ported vs manifold vacuum advance solved!!!

the main reason for vacuum advance is to be able to burn more completely lean mixtures at low load part throttle conditions and needing +40 degrees advance at those times to do so. This is for street cars I believe. I had heard of accelerated engine wear [carbon deposits etc] if I remember correctly if it wasn't used in a street car for any length of time
..and better idle performance, in that the AF mixture burns cleaner, and basically under any variable load condition the ignition timing adjusts to compensate, providing the greatest overall performance and in some/many cases a cleaner burn, reducing build-up of nastiness in the engine, and making the whales, spotted owls, and bluefin tuna happy...
 
I would love to be educated too and see no one laughed at you. I even removed that statement from your quote as many guys run without vacuum advance. There must have been a very good reason for all the car manufacturers to go to the trouble ,hassle and expense to install them on all their cars.
My car runs fine without it. I’ve done A/B testing though and found 2+ MPG difference in mileage and less propensity to run hot. I think that’s why the factory did it too.
 
Engine timing requirements depend on engine speed and LOAD. Mechanical adv handles engine speed, vacuum advance handles timing based on engine load. Main effect on fuel economy. Providing proper timing for Mid RPM cruise for example. They work together. Without both timing not correct at all operating conditions of the motor. Drag race cars always at WOT, no/low vacuum condition other than start line. So timing is different for a race car, versus street car. A stock mopar distributor would not have enough (correct adv) for mid throttle under load condition from mechanical alone. The Vacuum would add the advance. Then as you go WOT and mechanical maxes out, vacuum goes down and vacuum unit retards so that your total is where it is needed at WOT. Can you operate without it, yes. Fuel economy and proper combustion suffer.
 
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Engine timing requirements depend on engine speed and LOAD. Mechanical adv handles engine speed, vacuum advance handles timing based on engine load. Main effect on fuel economy. Providing proper timing for Mid RPM cruise for example. They work together. Without both timing not correct at all operating conditions of the motor. Drag race cars always at WOT, no/low vacuum condition other than start line. So timing is different for a race car, versus street car. A stock mopar distributor would not have enough (correct adv) for mid throttle under load condition from mechanical alone. The Vacuum would add the advance. Then as you go WOT and mechanical maxes out, vacuum goes down and vacuum unit retards so that your total is where it is needed at WOT. Can you operate without it, yes. Fuel economy and proper combustion suffer.

Very well said about timing. Thanks. As said vacuum advance is basically for part/mid throttle when the eng can take more timing since the mixture is not compressed real tight and takes longer to burn the eng needs to start the timing earlier in that condition. So at part throttle the vacuum is high and it can put timing anywhere from 35 to about 55 degrees at part throttle depending on the eng setup. Now at wide open throttle the mixture is much tighter compressed and burns faster so most engines only like around 35 to 40 timing on the engines of the 60's and 70's with old iron heads. The eng wont take the 50 plus degrees at WOT that it can take at part throttle. Thats why vacuum advance works so good since the vacuum drops to zero at WOT and then the eng just uses the mechanical advance. Drag race cars dont need the vacuum advance because they dont drive around at part throttle. They are at idle or floored basically. So vacuum advance is good for most engines and just needs to be set up right for the combo the eng is running. Ron
 
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100% agree! It is the distributor that is affected by the vacuum source, and just as Don at 4 seconds flat aka FBO Ignition Systems recommends...scratch that, INSISTS on manifold vacuum be connected to his distributor setups, as does my next ignition system from Progression Ignition. (calling Progression Ignition today w/a few questions, and fully expect to place my long awaited order)
The Progression Ignition uses the manifold vacuum for the same timing reason but in a different way. It will idle at whatever timing you set it at, but when you put an automatic in D or R, the vacuum will drop. The distributor will see the drop in vacuum at the normal idle speed and increase timing. If it was hooked to ported, it wouldn't see that drop in vacuum. It is a bit of a learning curve using Hg instead of vacuum though.
 
The Progression Ignition uses the manifold vacuum for the same timing reason but in a different way. It will idle at whatever timing you set it at, but when you put an automatic in D or R, the vacuum will drop. The distributor will see the drop in vacuum at the normal idle speed and increase timing. If it was hooked to ported, it wouldn't see that drop in vacuum. It is a bit of a learning curve using Hg instead of vacuum though.

The dist wont increase the timing when you put it in gear and vacuum drops a little. If the vacuum drops the vacuum advance will give less timing if you use manifold vacuum at idle. Using intake vacuum at idle has its good and bad points. Alot has to do with the combo as to how you use the vacuum advance. Ron
 
The dist wont increase the timing when you put it in gear and vacuum drops a little. If the vacuum drops the vacuum advance will give less timing if you use manifold vacuum at idle. Using intake vacuum at idle has its good and bad points. Alot has to do with the combo as to how you use the vacuum advance. Ron
@383man, please research the Progression Ignition distributor before comments.
 
The distributor will see the drop in vacuum at the normal idle speed and increase timing.
That "feature" of programmability is one of the things that I plan to use, but I have a manual transmission...
I just discussed this with Ted at Progression. I have added that Wraptor serpentine belt and accessories system, and Vintage Air was one of the additions. I thought about converting the solenoid that I don't use to idle (that "special" one the 6bbl comes from the factory with) and making it trigger when the AC compressor is on. Now I have to idle about 150 RPMs higher than needed to compensate for the compressor slowing my idle too low.
But
By setting up the Progression where, for example, my "normal" idle is 900 RPMs, I can program in a few + degrees from say 650-875 RPMs. Then the added advance should bring me back to around 900 with the AC on.
 
The dist wont increase the timing when you put it in gear and vacuum drops a little. If the vacuum drops the vacuum advance will give less timing if you use manifold vacuum at idle. Using intake vacuum at idle has its good and bad points. Alot has to do with the combo as to how you use the vacuum advance. Ron

It will increase timing but only if you program it that way.
 
@383man, please research the Progression Ignition distributor before comments.

I take it that its not a normal dist setup. I have not read about it yet but will and if that is how it works then I apologize for me not taking the time to look into it. I was just asuming you were talking about a normal dist and did not understand it but it looks like I may be the one wrong as I will take the time to read about it. Thanks , Ron
 
I agree with Edelbock. A proper manifold vacuum advance system will improve idle quality, help your engine run cooler, if it’s of any importance to you - improve gas mileage and doesn’t affect street performance in the least. Ported vacuum advance was a aberration of frustrated emissions engineers staggering around in a dark world.
Then why is the original AFB from my 67 R/T ONLY have the Ported nipple? Manifold didn't make an appearance until later, or on Edel AFBs.
 
I agree with Edelbock. A proper manifold vacuum advance system will improve idle quality, help your engine run cooler, if it’s of any importance to you - improve gas mileage and doesn’t affect street performance in the least. Ported vacuum advance was a aberration of frustrated emissions engineers staggering around in a dark world.
Then why does the original AFB in my R/T only have PORTED vacuum. No manifold vaccuum until later, and with the Edel AFBs.
 
Actually, the guy is correct but it can be difficult to set up manifold vacuum advance when running a lot of initial advance and many don't have the patience or understanding to do it.

Ported advance came along when emissions first raised its head. Too much initial advance increase NOX (NO2) so the factories started removing initial advance and sometimes even went from before top dead center to after top dead center to be able to pass emissions requirements.

Once the butterflies open a little, ported vacuum and manifold vacuum reach the same level and the effect upon timing is the same. Put a vacuum gauge on each port and start opening the throttle. The gauges will quickly read the same.

Mechanical advance is dependent upon rpm solely whereas vacuum advance is a function of load (load increases, vacuum drops).

The benefit of adding vacuum sourced advance comes in improved cruising mileage when the total advance between mechanical and added vacuum rises to somewhere around 45-50 degrees.

A problem arises when one runs a lot of initial advance and the vacuum starts increasing the advance above the mechanical advance and we get light throttle detonation at cruise or the applied vacuum does not drop immediately when the throttle is cracked for acceleration and the timing does not drop back to the mechanical advance only.

The problem is complicated by compression ratio and camshaft duration.

It becomes a juggling act. Adjustable vacuum advances are available to trigger the activation point and one also can limit the total amount of available by limiting the total available from the vacuum can rod movement.

If one does a lot of cruising, then one might like to get a couple of mpg by learning how to set the ignition up. If one does not do any real highway driving and just wants to play on the street, then it is probably way too much hassle.

In the end, vacuum is vacuum whether comes through the manifold port or the ported vacuum port. The only difference is at idle and just off idle.

Ported was invented to try to beat the emissions requirement at idle with regard to NOX.

EFI solves most of the problem when it comes to performance.
They why does the original AFB in my 67 R/T have ONLY ported vacuum?
 
Damm,
Man Vac Adv [ MVA ] was around for years, used by GM until 1967-8. Not sure about Ferd & others. Then emissions forced the use of the USELESS PVA.
Chrysler, stupidly, chose not to use MVA during the performance years. That is why your AFB has the PVA port. MVA does not need a dedicated port [ but it often does ], it can be connected to a manifold runner or Tee-d into the brake booster line.
The paradox is that Ch was forced to use MVA in the 1970s when emissions raised engine temps. MVA would be switched on when temp reached 200+*......to cool the engine.
Folks should think about how/why MVA cools an engine....
 
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