AJ/FormS
68 Formua-S fastback clone 367/A833/GVod/3.55s
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- Jan 19, 2014
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I hear what you are saying.
By now you realize that it is just more than the vacuum advance that is effecting the tuning of your engine the timing curve, the fuel, cam and the converter they all work as a team to provide performance. If one player is not right it can/will effect the other players and performance will suffer.Yea I read so much stuff on here I forgot alot of the stuff by the time I need to use it and then have to go back and reeread it lol. Thanks again bud I will go back and read all that again.
Adjustable vac adv units.
From maaaaany years of experience with various brands.
[1] The Crane unit is probably the best known. It is also the stupidest design. Along with Accel [ & I think Mr. Gasket ], there is a spacer inside the spring. If you wind the the wrench in, it locks up! You get no VA. With these, I uncrimp the can & remove the spacer. The best adj VA units I have found come with Chinese dists
[2] VA has two adjustments. Rate, adjusted by using the wrench to change spring tension. And Total or amount of VA added. This requires some form of stop or limiter to limit plunger travel. I have found that in the majority of cases, the total amount will need to be limited. Too much VA [ ported or manifold sourced ] usually manifests it self as light surging &/or slight misfire. The concept of VA then gets blamed [ 'didn't work for me' ] when the real problem is that it was not dialled in properly.
Couple of general comments.
[3] The Crane instructions say to connect to manifold vacuum.
[4] Some of you are probably aware of, or even use, Progression Ignition dists, with models to suit Chrysler engines. Page 4 of the instructions say to connect to manifold vacuum. In upper case letters it says, 'DO NOT connect to ported vacuum'.
Nice write up guysHere is an old article with a lot of info. Keep it for reference and read the whole thing.
Cal Tech
Advance To Go
I just saw this post thanks for sharing. That makes more sense than anything iv read before and I completely agree. I was using 318willruns method of timing setting, basically he just keeps bumping up his timing at idle till the idle no longer increases or it stops idling smooth. Then backs it off 2 to 4 degrees which landed me at 20 degrees. I got all the way up to 24 degrees before it stopped increasing. And it seemed to run really good there. So using MVA I could set my initial at lets say 10* intial and using mva id be back at 24* during idle. Until the engine is under load. I guess im just gonna have to play around with it different ways and see what my engine likes. I appreciate all the help I have a much better understanding of the difference now!To Dartfreak 75.
The only difference between PVA & MVA is that MVA is operating at idle, PVA is not.
I suspect your engine will benefit from MVA. Easy to tell. Hook it up! If idle rpm increases & idle is smoother, then the engine likes it. It may not want all of the available advance that the VA can can deliver, so a stop would need to be fabricated to limit the total VA.
The difference between a locked dist providing, say, 34* at idle & MVA giving 34* is that the engine is always going to see 34* with a locked dist, which might produce pinging. MVA is load sensitive, so the 34* will reduce to a lower number under load.
You would be surprised how much extra idling timing even stock engines like.
Example: Pontiacs idled with 26*, 6* init + 20* MVA. These were high comp engines [ 10.75 ] with mild cams. Lower CR, more cam duration, needs more idle/cruise timing.
What is different between a Pontiac & a Mopar? They are made of cast iron & ingest fuel & air.
I don't understand what you mean by hitting stall? What does the stall have do with timing or detonation?beware the dreaded idle tip-in hesitation that takes extra pump-shot to overcome, and maybe you run out of shot 1/2 second later.....
I gotta repeat;
with an automatic, who cares about the timing below stall..... even 10 degrees short will not be missed.
But if you hit stall at WOT, with even 1* too much, over time, you are probably gonna detonate the plugs to pieces. And those ceramic bits are about three times as hard as steel..... 2200rpm is one revolution every .0273 seconds, which on a V8 is 4 firings. When you hear the detonation, IF you hear it, it might take you .5 second to lift off the throttle. In that time, your engine has fired 73 times................. where are the bits, and what are they doing?
At 2200 and cruising, your engine might want 56* of timing, for best fuel-economy.
If you run 12 mechanical at idle, and an additional 12 in the can, what happens at 2200 and cruising?
I'll tell you
Your max Power-Timing with a lo-compression 318 might be 36* at 3400rpm. To get to 36 from 12 is 24 degrees. And if your curve begins at 1000, then you have 2400 degrees to get there. This maths out to 1.0 degree per 100 rpm.
Therefore, at 2200 the mechanical timing will be 12+12=24. And in this case, the Vcan is bringing 12 to the table so 24+12=36 at 2200 and cruising.
But your engine might want 56*! so you are 20* short, and no wonder the thing is a pig on gas.
You said it; For power, the engine doesn't care about any timing below the stall-rpm.But just trying to give the engine the timing it wants at stall is a very big deal .What does the stall have do with timing or detonation?
Mumbo jumboDid you get the timing sorted out, the standard Mopar performance distributor curve should be real close.
There's fair amount of mumbo jumbo going on in this thread. lol
Did you get the timing sorted out, the standard Mopar performance distributor curve should be real close.
There's fair amount of mumbo jumbo going on in this thread. lol
Not yet I haven't even had a chance to work on it any yet.Did you get the timing sorted out, the standard Mopar performance distributor curve should be real close.
There's fair amount of mumbo jumbo going on in this thread. lol
Thanks for this much appreciated!
Thanks for this much appreciated!
Note the above testing procedures shown in posts 67-69 for dialling in vac adv will produce exactly the same results whether the VA was connected to ported or man vacuum. It makes no difference. Man vac cleans up the idle & tip in, ported doesn't operate at idle.
I never didn't believe you said to run ported from the beginning and I said thanks I haven't questioned that. Other ppl have chimed in and made good points and I have a better understanding of the whole process now! Im the type of person I don't want to just know how to do it want to know why I'm doing it that way and what will happen if I don't do it that way. Please don't take offense if I keep asking questions I always heed everything you say you have never lead me wrong im just the type of person a simple how to answer just isn't enough. And that's how you learn and expand your capabilities. It's easy to learn that 2+2=4 and memorized that but what happens when you get 3+1? Its still 4 your just getting there im a different way. But I never once 2nd guessed you or your advice! Sorry if I made you feel that I did.So did somebody finally get through? I'm glad you believe somebody for a change.
I never didn't believe you said to run ported from the beginning and I said thanks I haven't questioned that. Other ppl have chimed in and made good points and I have a better understanding of the whole process now! Im the type of person I don't want to just know how to do it want to know why I'm doing it that way and what will happen if I don't do it that way. Please don't take offense if I keep asking questions I always heed everything you say you have never lead me wrong im just the type of person a simple how to answer just isn't enough. And that's how you learn and expand your capabilities. It's easy to learn that 2+2=4 and memorized that but what happens when you get 3+1? Its still 4 your just getting there im a different way. But I never once 2nd guessed you or your advice! Sorry if I made you feel that I did.