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Are you “Steve” that does the Charger conversions?
Ported vacuum advance or manifold. Let's debate!
- Thread starter Kern Dog
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Hemirunner
Well-Known Member
No. I’m a drag racer/ engine builder from the midwest.
Wietse
Well-Known Member
You are probably running quite some cam with 50*at idle.
Mine is not stock either, using ported throws too much timing in when you give light throttle and it instantly pings. Reducing initial advance and using manifold vacuum sorts that out.
I guess it comes down to what/how the engine is build. It is not something you choose by preference or make/model of engine, it is what the engine setup requires.
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Let's clear this up with an experiment.
1. Everyone use manifold vacuum for five years.
2. Everyone switch to ported vacuum for another five years.
3. In ten years, compare notes on how the cars performed each way.
1. Everyone use manifold vacuum for five years.
2. Everyone switch to ported vacuum for another five years.
3. In ten years, compare notes on how the cars performed each way.
4406bbl
Well-Known Member
Your ignorance is amazing. Always trying to stir sheet up. Everyone else figured it out. Fixed it for you.
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And here it is, the entertainment 
parksr5
Member
Personally, in the last number of years when thinking of doing something to my cars, I consume as much information as I can and take everything into consideration but then, I test everything. I just made some changes earlier this year and tried both ported and manifold vacuum and I went with the one the ran the best, all around and didn't care which one it was.
There are too many variables to say one way is the right way in all situations. In the end, I don't care what someone else thinks about what I did, and I don't care what they do with their car. If the ultimate goal is to make a car run the best it can and I accomplish that, I don't really care if someone else thinks what I did is wrong. Think Engine Masters. The only way to know what something will and will not do is to test it. No one 20 years ago would have said that putting a bunch of dents in headers would have made more power on a dyno than none dented headers but, they proved that wrong. With all things, in theory, "x" should have "x" impact but, you don't know until you try it and see what your combination wants and how your combination reacts.
There are too many variables to say one way is the right way in all situations. In the end, I don't care what someone else thinks about what I did, and I don't care what they do with their car. If the ultimate goal is to make a car run the best it can and I accomplish that, I don't really care if someone else thinks what I did is wrong. Think Engine Masters. The only way to know what something will and will not do is to test it. No one 20 years ago would have said that putting a bunch of dents in headers would have made more power on a dyno than none dented headers but, they proved that wrong. With all things, in theory, "x" should have "x" impact but, you don't know until you try it and see what your combination wants and how your combination reacts.
Hemirunner
Well-Known Member
Think about timing vs piston position in the cylinder then consider timing vs rpm. As the piston comes up, you need advance in order to fire the charge at the appropriate moment to burn the charge and produce the proper pressure wave to apply force downward on the piston. Too much and you could bend a rod (Under load) and too little you give up power with late/incomplete burn. As rpm increases, you need less advance as the piston speed has increased, decreasing the amount of time available between bdc and tdc.
At idle, a typical 4 stroke gasoline engine will idle on anything from 5 degrees on up depending on the engine combination as you have the most time available between bdc and tdc. Low timing values here only serve to deliver a poor burn and put excessive heat in the engine. At it simplest, MVA adds timing where needed and removes it where it’s not.
Both timing methods can be configured to work and work well but the user has to understand what timing is needed for a given set of conditions in a given engine combination and build a curve accordingly. In order to do this, one has to understand the typical distributor has 3 distinctly different timing functions, initial, mechanical and vacuum. You can set the range of each (How much timing) independently and control the “when” portion of the mechanical with different springs and the vacuum advance portion through the use of either PVA vs MVA to build the desired curve.
Very few take the time to learn and understand it and the same can be said for carburetors, but that’s a whole nuther subject.
At idle, a typical 4 stroke gasoline engine will idle on anything from 5 degrees on up depending on the engine combination as you have the most time available between bdc and tdc. Low timing values here only serve to deliver a poor burn and put excessive heat in the engine. At it simplest, MVA adds timing where needed and removes it where it’s not.
Both timing methods can be configured to work and work well but the user has to understand what timing is needed for a given set of conditions in a given engine combination and build a curve accordingly. In order to do this, one has to understand the typical distributor has 3 distinctly different timing functions, initial, mechanical and vacuum. You can set the range of each (How much timing) independently and control the “when” portion of the mechanical with different springs and the vacuum advance portion through the use of either PVA vs MVA to build the desired curve.
Very few take the time to learn and understand it and the same can be said for carburetors, but that’s a whole nuther subject.
66 Sat
Well-Known Member
Geoff, if you hit +Quote and then Insert Quote on the post you agree/disagree with, it includes it in your next post. That way you don't have to keep referring to post numbers and making members go back to pages to see what you're on about.
Post #15 couldn't be taken 2 ways.
You just read it wrong and shot from the hip.
The response of "No vacuum advance is not the best for a street driven car." was correct and in direct response to post #14 which said
"What about, no vacuum advance at all?"
Last edited:
diesel_lv
Well-Known Member
And it's "very" easy to "ask" what that person meant instead of "assuming" it was one of the 2 and calling them ignorant. Goes both ways.
Wietse
Well-Known Member
Now is English not my native language, but I do understand what 4406bbl is saying here, and I agree with it.
It's a double negative. Ask @Kern Dog. "Vacuum advance is best for a street driven car."
Eric F
Active Member
I’ve been an automotive technician since 1980. High school auto shop, Arizona Automotive Institute. Many automotive college classes. A Chrysler tech since 1985. All my years of training both Manufacture and independent. The Vacuum advance always goes to the ported point on the carb. We were taught the engine needs a gradual timing curve for best overall performance. When I used to race my car in the 80’s . Vacuum advance was disconnected and the total curve in the distributor was reduced and made to advance quicker. Then more initial timing was put in.
Wietse
Well-Known Member
To me both mean the same thing
diesel_lv
Well-Known Member
All "college" automotive classes teach what is being manufactured. By the 70's all were using port for emissions reasons. So by the time you or I started learning, the only thing taught was port. But, in a modified engine or engine not worrying about emissions, manifold vacuum can be very beneficial.
68 HEMI GTS
Well-Known Member
Love the arguments
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