diesel_lv
Well-Known Member
Ported and manifold vacuum are the same once you crack the throttle and start to drive away. The ported source "gets" its vacuum "from" the manifold.
Ported vacuum advance or manifold. Let's debate!
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4406bbl
Well-Known Member
With manifold source your cruise vacuum advance degrees will stay the same, your idle advance degrees should go up depending on the idle vacuum and where the vacuum can starts, your throttle position should close a bit. You will always want to be sure your initial and mechanical combined are correct for wide open throttle first, I will assume you need about 35-36 degrees with your heads, never more than 38 for those heads. If it still diesels an idle dashpot like the 6bbl mopar cars had will help. Lowering the idle to fix dieseling kind of defeats the purpose of manifold vacuum because the engine vacuum goes down with the idle speed. I think I explained it right. Generally it is best with low vacuum to have a lot of initial, pull in mechanical fast up to your target of 35 or whatever it is, then work the vacuum can. The starter on a 100 degree day is usually the limiting factor on how much initial you can run. This applies to manual trans cars, with an automatic with a stock torque converter, and big cam good luck, as when you drop it in gear the vacuum drops, rpms drop, timing goes down, and you have a fun car at stop lights. Ported vacuum and lots of initial, or a $$$$ torque converter is the key here. The kind of torque converter you make a phone call to a manufacturer and explain your situaton to buy.
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Wietse
Well-Known Member
Yes, but since you opened the throttle the vacuum drops, then will give less advance.
I tried several times on ported but when being gentle on the throttle i can hear i ping, when going back to manifold vacuum there is no ping.
For the ported i need to turn back the initial advance to less, say to 10-12 degrees, and then it will not idle at all.
Dragon Slayer
Well-Known Member
Last I check this is a mopar forum with Chrysler products. GM used different strategy had Air pumps on the cars etc...
I could say your optimizing your car for idle performance, and other might want to optimize for high speed, cruise etc...
Lastly, from the beginning it was about fuel economy. Emissions did not become important until the 60s with mandatory in 66 for CA, and 68 for all states. BUT fuel economy was King from the beginning. So you are wrong. Chrysler chose ported before emissions were and issue. Kept it when emissions became king, modified carb, distributor, and used a vacuum device to meet the requirements.
So what is best varies. What is for sure is Chrysler designed for ported. So if your carb, distributor, motor are stock or near stock it will work. But if you're deviating from stock other methods might work better. Last time we had this argument you ignored that Pontiac even had retarded timing devices/features to make it work. Chrysler did it also with Manual trans cars and hemi. On deacceleration the distributor device would shift to manifold to ensure timing stayed advance while throttles closed but car still at higher rpm deaccelerating.
Folks just need to remember that if you're using a chrysler distributor chances are you have 15deg cams that provide 30deg mechanical timing at crank. You have Vacuum advances with 10 or 11deg arms that provide up to 20deg at the crank. Plus, whatever initial timing you're using. So at idle it may be working great for you, but how the timing curve comes down and how fast it comes downs determines if you get into detonation as you accelerate since you're at 50deg advance to start and your goal is 36 or so.
Nothing I said above means I said Ported is better. I just disagree with you that manifold is the best always. Which is your point.
I said in the previous thread that I believe both can be made to work well, or work poorly. It's all about understanding how each affects the car. There is not one simple answer that will work in all cases. Compression, vacuum at idle, settings for vacuum canister and distributor, carb size, etc. will all play a role for how the car behaves.
A person who uses MVA will generally need to reduce their static timing since vacuum advance at idle will increase timing. Conversely, someone using PVA will have a tendency to increase their static timing since there will be no vacuum advance at idle.
But let's think of a couple of scenarios:
(Case #1) Running MVA with an aggressive cam so the engine makes low vacuum at idle. In this case, the initial timing is set higher, and the MVA adds only a little bit of timing. When this person starts to accelerate, the timing does not drop off very much, and then centrifugal advance starts to take over.
(Case #2) Running MVA with a cam that makes a lot of vacuum at idle. In this case, the initial timing is set lower, and the MVA adds perhaps 20 degrees of timing. When this person starts to accelerate, the timing drops off by 20 degrees until the centrifugal advance can start to increase it back. I believe that this case the car will perform better with PVA (set correctly) so the timing doesn't fall on its face when accelerating. Of course, there is SO MUCH that is tunable. As mentioned earlier, when and how much timing the vacuum advance and centrifugal advance apply can be adjusted.
VERY ROUGHLY, and based on most common settings for centrifugal and vacuum advance, I would say that a cam that produces high vacuum at idle may run better when tuned with PVA. Conversely, a car with an aggressive cam may run better with MVA.
Let the flaming begin...
A person who uses MVA will generally need to reduce their static timing since vacuum advance at idle will increase timing. Conversely, someone using PVA will have a tendency to increase their static timing since there will be no vacuum advance at idle.
But let's think of a couple of scenarios:
(Case #1) Running MVA with an aggressive cam so the engine makes low vacuum at idle. In this case, the initial timing is set higher, and the MVA adds only a little bit of timing. When this person starts to accelerate, the timing does not drop off very much, and then centrifugal advance starts to take over.
(Case #2) Running MVA with a cam that makes a lot of vacuum at idle. In this case, the initial timing is set lower, and the MVA adds perhaps 20 degrees of timing. When this person starts to accelerate, the timing drops off by 20 degrees until the centrifugal advance can start to increase it back. I believe that this case the car will perform better with PVA (set correctly) so the timing doesn't fall on its face when accelerating. Of course, there is SO MUCH that is tunable. As mentioned earlier, when and how much timing the vacuum advance and centrifugal advance apply can be adjusted.
VERY ROUGHLY, and based on most common settings for centrifugal and vacuum advance, I would say that a cam that produces high vacuum at idle may run better when tuned with PVA. Conversely, a car with an aggressive cam may run better with MVA.
Let the flaming begin...
Wietse
Well-Known Member
Correct, and how one may achieve 30+ deg advance at idle with ported vacuum?
You can't.
Well, swap the cam to a stock one and be able to idle with only 10* of advance.
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How about this:
Wietse
Well-Known Member
Nah, i just flipped the monitor on it's side. 
Hemirunner
Well-Known Member
The best solution is EFI with programmable everything and data acquisition, but everyone’s definition of best differs as much as the problem being solved.
Wietse
Well-Known Member
I am currently installing hyperspark to go with my sniper EFI, only needs MAP sensor. 
4406bbl
Well-Known Member
And while we are on the subject, mopars were the cars that had gear reduction starters so they could tolerate more initial advance, gm cars would not start hot. Gm muscle cars were also the ones that ran hot, and overheated all the time, not the mopars. I also never said manifold vacuum advance could not work, just gm may have had no other choice. It used to be funny to hear gm cars try to start at rest areas in the 70s on hot days....they definitely got to rest.
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I never noticed a hot start problem with any of my gm cars.
Geoff 2
Well-Known Member
Post #64.
Dragon Slayer.
Which Pontiac cars had retarded timing devices to make 'it' work? Which devices & to make 'what' work? My 66 has no timing retard device on the ign.
And no, I am not wrong, you are.......again with this claim: 'it is about fuel economy', it being the use of PVA. If you knew anything about the subject, then you should know that MVA only makes a difference at idle when compared to PVA. At cruise, both act the same. But at idle, the extra timing provided by MVA uses less fuel, so OVERALL FUEL CONSUMPTION AND ECONOMY IS BETTER WITH MVA.
The car companies using MVA had to switch to PVA for emission reasons because the HCs were lower. Nothing to do with economy. And no amount of spin from you will change simple facts.
From D. Vizard's Holley book, p. 38:
'To get an optimum idle for the least amount of fuel consumed, timing often needs to be as much as 45-50* BTDC.'
P. 30: ' Minimum fuel consumption at idle usually entails pulling in 25* or more of additional timing'.
Dragon Slayer.
Which Pontiac cars had retarded timing devices to make 'it' work? Which devices & to make 'what' work? My 66 has no timing retard device on the ign.
And no, I am not wrong, you are.......again with this claim: 'it is about fuel economy', it being the use of PVA. If you knew anything about the subject, then you should know that MVA only makes a difference at idle when compared to PVA. At cruise, both act the same. But at idle, the extra timing provided by MVA uses less fuel, so OVERALL FUEL CONSUMPTION AND ECONOMY IS BETTER WITH MVA.
The car companies using MVA had to switch to PVA for emission reasons because the HCs were lower. Nothing to do with economy. And no amount of spin from you will change simple facts.
From D. Vizard's Holley book, p. 38:
'To get an optimum idle for the least amount of fuel consumed, timing often needs to be as much as 45-50* BTDC.'
P. 30: ' Minimum fuel consumption at idle usually entails pulling in 25* or more of additional timing'.
Geoff 2
Well-Known Member
AR67,
There are errors on the Woodruff site. Among the carbs listed as having 11/16" pumps are the 4428 & 4429 AVS carbs. I have these carbs & each have 3/4" pumps.
The best site I have found for Carter Info is the Carburetor Shop, Eldon, Missouri.
He states there four pump sizes for AFBs 9/16", 5/8", 11/16" & 3/4".
Out of curiosity, I bench tested an AFB today. Filled the bowl 1/2 full. Pushed the plunger with my finger. Instant fuel delivery at the nozzle. The spring on the pump shaft did not compress, the spring under the pump did. That is how it is supposed to work.
There are errors on the Woodruff site. Among the carbs listed as having 11/16" pumps are the 4428 & 4429 AVS carbs. I have these carbs & each have 3/4" pumps.
The best site I have found for Carter Info is the Carburetor Shop, Eldon, Missouri.
He states there four pump sizes for AFBs 9/16", 5/8", 11/16" & 3/4".
Out of curiosity, I bench tested an AFB today. Filled the bowl 1/2 full. Pushed the plunger with my finger. Instant fuel delivery at the nozzle. The spring on the pump shaft did not compress, the spring under the pump did. That is how it is supposed to work.
Dragon Slayer
Well-Known Member
This is why a lot of people think you are a jerk, you alway attack the person, vice the content of the post. I know how distributors and carburetors work. I also try NOT to give advice if I don't know what I am talking about. But we all make mistakes. You always have an answer and many case when you don't have any experience either. Like the hemi carb conversation. Nothing I said is wrong and I have not declared one is better than the other. Kern Dog can do what he wants, but these MVA versus Ported seem to always end this way. BUt I find the arguement usless at times, as people are comparing turbo charged EFI setups with carburetor cars etc... Not an apple-to-apple comparison.
Dragon Slayer
Well-Known Member
You on the wrong post with this. Your also wrong. The 4429 uses the same 64-212 11/16" pump as other mopar AFB. The 4428 uses the 64-279 also 11/16" but no anti perculate check ball. It was 69 AVS that moved to a different pump and pump size.
Hemirunner
Well-Known Member
The induction system has virtually nothing to do with the timing requirements. The compression ratio, camshaft profile, fuel type and cylinder head style will have way more bearing on timing than induction.
Dragon Slayer
Well-Known Member
I think it does still have an effect because it has an effect on fuel mixture quality and distribution which would have an effect on timing needs. The bottom line to me is your motor is not a good example for someone trying to figure out what to do with a carbureted non turbo motor. Plus your using an engine management system too.
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