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Ported vacuum advance or manifold. Let's debate!

What Geoff said X 2. If you’re restoring one of these heaps, use PVA like the factory did so it’s “correct”. (Air quotes because I’m not a purist) For everything else use MVA.
I have 50 degrees of total timing in at idle.
Are you “Steve” that does the Charger conversions?
 
What Geoff said X 2. If you’re restoring one of these heaps, use PVA like the factory did so it’s “correct”. (Air quotes because I’m not a purist) For everything else use MVA.
I have 50 degrees of total timing in at idle.
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.
 
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.
 
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.
:rofl: :rofl:
 
[1] Cannot believe the ignorance, post #15.
[2] GM used MVA up to the late 60s, when tighter emissions forced the use of the USELESS PVA. MVA produced more HC than PVA, hence it's demise.
[3] Rarely would a street driven car/engine not benefit from MVA. One case would be locked timing, but even some of these would benefit from a small amount of timing added by MVA.
[4] If the engine was a candidate for MVA [ & most are ], then there is no such thing as it didn't work for me'. What happened was it wasn't dialled in properly. Unfortunately, I have never seen a method quoted, so I developed my own 25 yrs ago. Some of it is in the thread 'Carburetor Tuning' in this section. I suggest you read it & also see what D. Vizard said.
[5] GM cars. As an example. My GTO was driven off the showroom floor, idling at 26*. 6* initial + 20* added from MVA. 10.75:1 comp ratio, mild cam 200* @ 050.
[6] Chry missed the boat on MVA, that simple.
Your ignorance is amazing. Always trying to stir sheet up. Everyone else figured it out. Fixed it for you.
 
Exactly, no way to have a constructive discussion.
 
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.
 
Post #28,
Yes hard to have a constructive discussion when you post a statement that can be taken two ways.
 
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.
 
Post #28,
Yes hard to have a constructive discussion when you post a statement that can be taken two ways.
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?"
 
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Post #28,
Yes hard to have a constructive discussion when you post a statement that can be taken two ways.
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.
 
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.
 
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.
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.
 
Love the arguments

:lol:

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