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Username Post: vacuum advance canister        (Topic#356508)
995jim 
Contributor
Posts: 468
995jim
Loc: Ohio
Reg: 12-17-06
05-20-19 05:03 PM - Post#2766823    

Hi, I just installed a new adjustable vacuum advance canister on my 402 chevy HEI dist.The instructions say to advance the timing 2 degrees above current advance, then proceed with adjustments. My first question is what is the purpose of over advancing the 2 degrees?
Also is it any better or worse to pull vacuum for the canister from the carb or intake manifold?
thanks jim

Jim

65' Impala SS, 65' Belair, 89' Silverado Z71, 95' Silverado Z71, 12' Silverado, 15' Silverado LTZ, 16' Tahoe LTZ


 


rumrumm 
"18th Year" Silver Supporting Member
Posts: 2086
rumrumm
Loc: Macomb, IL
Reg: 10-18-01
05-21-19 07:38 AM - Post#2766841    
    In response to 995jim

I cannot answer your first question, but the answer to your second question is you should run your vacuum advance from the manifold vacuum port from your carburetor.

Lynn

"There's no 12-step program for stupid."


383 sbc, Eagle, AFR, SRP, CompCams, Edelbrock, FiTECH. Dyno #'s: 450 hp @ 5700, 468 lb. ft. of torque @ 4300.



 
IgnitionMan 
Valued Contributor
Posts: 3667

Reg: 04-15-05
05-21-19 09:14 AM - Post#2766849    
    In response to 995jim

Which particular vacuum advance, and if it was a Crane, where did you mount the degrees stop plate?



 
995jim 
Contributor
Posts: 468
995jim
Loc: Ohio
Reg: 12-17-06
05-21-19 04:35 PM - Post#2766884    
    In response to IgnitionMan

its a jegs brand adjustable by using the allen wrench inside the vac tube. I talked to sales tech and the response was to give engine a leaner burn. I didn't really understand the response. I figured the advance should be 18 btc whether or not the engine has a vac advance canister.

Jim

65' Impala SS, 65' Belair, 89' Silverado Z71, 95' Silverado Z71, 12' Silverado, 15' Silverado LTZ, 16' Tahoe LTZ


 
IgnitionMan 
Valued Contributor
Posts: 3667

Reg: 04-15-05
05-22-19 01:27 AM - Post#2766912    
    In response to 995jim

Of there is no separate degree adjustment stop plate, it is all the way useless. The Allen wrench setting in the diaphragm, is to adjust the vacuum rate the advance works within, NOT to adjust degrees of timing added.

As far as the "tech" goes, more usdlezz info on building be at, he Did an t know that to do that, is to use a fully functional EGR valve and its ported vacuum source, ,KT full manifold vacuum to help non-EGR type engines.

Now, do you have a degree stop plate on the advance, and if so, where is it mounted? No plate, no fix it right.






 
japete92 
"5th Year" Silver Supporting Member
Posts: 1248
japete92
Loc: No. Virginia
Reg: 01-18-13
05-22-19 07:51 AM - Post#2766923    
    In response to 995jim

This may be helpful to you:

https://www.chevelles.com/forums/13-performance /18...

Pete



 
995jim 
Contributor
Posts: 468
995jim
Loc: Ohio
Reg: 12-17-06
05-22-19 05:46 PM - Post#2766959    
    In response to IgnitionMan

Currently there is a stop pate mounted exactly where the vac canister would bolt down to in the distributor and the rod length/bolt hole pattern matches exactly to the vac canister

Jim

65' Impala SS, 65' Belair, 89' Silverado Z71, 95' Silverado Z71, 12' Silverado, 15' Silverado LTZ, 16' Tahoe LTZ


 
IgnitionMan 
Valued Contributor
Posts: 3667

Reg: 04-15-05
05-22-19 07:04 PM - Post#2766960    
    In response to 995jim

Jim, I don't fully get what you are saying, so I will outline it, and hope we are on the same page.

Crane adjustable vacuum advance kits have a scroll plate that is there to limit the number of degrees the advance gives. It is a small plate, curved round, with a series of serrated cuts that fit the pull pin when installed. This plate is also available separately, to mount to other advances.

Crane says to mount the plate to the end vacuum advance hold down screw, which pushes the pull pin INTO the diaphragm as degrees are removed.

If that is the case, the plate is mounted on the wrong side of the pin. Pushing the pin into the diaphragm as degrees are stopped down isn't the right way to do it, as the diaphragm spring is tightened with every adjustment to reduce degrees, and within two turns of the diaphragm spring, the vacuum rating is why past working for any engine.

We actually want to stop the pull pin in its travel to limit degrees of vacuum advance. This separates the vacuum pull rate frm the degrees availble. This method doesn't push the pin into the diaphragm, it stops the pin when its travel produces the desired amount of degrees.

Now, nobody get out of shape with this, IT AIN'T an ad, but, there are pictures of the stop plate and it mounted correctly on my web site. I also can send you complete info on mounting the plate correctly, it isn't hard, and that should get you an advance that has separate vacuum rating and degrees adjustments.

We can go forth from there with proper curves and curve speeds, what vacuum to run, degrees, and theory/application.

If I am right, you are only a hex head machine screw, flat washer and drilled/tapped hole from getting the stop plate correct.

If you want to view the vacuum advance stop plate mounting package, send me an email and I will send it to you, NO CHARGE.

gmvacuumadvancemodificati ons@gmail.com

The other common misinformation on adjustable vacuum advance is that the Allen screw adjustment inside the diaphragm on those advances that do not have a stop plate, adjusts the available degrees correctly, is false. If we think about it, changing the vacuum rating by "adjusting the diaphragm travel" not only changes the degrees available, but also does the same as the Crane with the stop plate mounted on the end screw, closes the travel down to decrease degrees, and pushes the diaphragm into the spring, and, not far after that, we run out of adjustment to reduce the spring tension for lower vacuum, we render the advance useless.

When properly set up, the adjustable vacuum advance with plate mounted in the correct place benefits so much, not causes more trouble.



 
995jim 
Contributor
Posts: 468
995jim
Loc: Ohio
Reg: 12-17-06
05-23-19 05:39 PM - Post#2766999    
    In response to IgnitionMan

Sorry , I gave you an incorrect description of what I have. The dist has a vac advance lockout not a stop plate so I will have to get a stop plate then.

Jim

65' Impala SS, 65' Belair, 89' Silverado Z71, 95' Silverado Z71, 12' Silverado, 15' Silverado LTZ, 16' Tahoe LTZ


 
IgnitionMan 
Valued Contributor
Posts: 3667

Reg: 04-15-05
05-23-19 07:02 PM - Post#2767003    
    In response to 995jim

So, there is no vacuum advance at all? Or, one is there, but the vac adv is locked out?

What specific distributor is it we are discussing???



 
995jim 
Contributor
Posts: 468
995jim
Loc: Ohio
Reg: 12-17-06
05-25-19 03:48 PM - Post#2767080    
    In response to IgnitionMan

no vac advance at all. thanks, jim

Jim

65' Impala SS, 65' Belair, 89' Silverado Z71, 95' Silverado Z71, 12' Silverado, 15' Silverado LTZ, 16' Tahoe LTZ


 
IgnitionMan 
Valued Contributor
Posts: 3667

Reg: 04-15-05
05-26-19 07:52 AM - Post#2767099    
    In response to 995jim

1/4 mile drag race only vehicle?

Not driven on the street?

No vacuum advance, for a street driven engine, not good.

The confusing part, "Hi, I just installed a new adjustable vacuum advance canister on my 402 chevy HEI dist.The instructions say to advance the timing 2 degrees above current advance, then proceed with adjustments. My first question is what is the purpose of over advancing the 2 degrees?
Also is it any better or worse to pull vacuum for the canister from the carb or intake manifold?"



 
995jim 
Contributor
Posts: 468
995jim
Loc: Ohio
Reg: 12-17-06
05-28-19 03:30 PM - Post#2767245    
    In response to IgnitionMan

Im sorry about my post as what I was thinking I simply wasn't saying. The car is just a driver with a 402 I had rebuilt from a local engine shop. The engine compression is 8.5 to 1 as I wanted pump gas. cam is dur .050 intake219 ex 219 lobe lift .2860 separation 110. I also had forged pistons. I see red and yellow springs on the distributor advance weights,HEI dist with a vac advance lockout plate installed where the vac canister would be installed which there is not currently
, 400 trans,750 edelbrock,3;73 rear posi,and hooker headers. No EGR, stealth inake, Hope this info gives a little more insight to my original question. thanks jim

Jim

65' Impala SS, 65' Belair, 89' Silverado Z71, 95' Silverado Z71, 12' Silverado, 15' Silverado LTZ, 16' Tahoe LTZ


Edited by 995jim on 05-28-19 04:20 PM. Reason for edit: No reason given.

 
IgnitionMan 
Valued Contributor
Posts: 3667

Reg: 04-15-05
05-29-19 05:49 AM - Post#2767273    
    In response to 995jim

Ok, now we have a much better insight. On your engine combo, a correctly set up vacuum advance will help immensely.

Initial of 12

Vacuum advance set to 10 to 12, on full manifold vacuum, for an idle timing of 22/24

Mechanical to give 22 degrees for a 34 degree total, start curve 100/150 rpms over idle speed, limit 2,800 to 3,000 rpms, should run really good.

If you go with a Crane adjustable vac adv, and set the degrees stop plate up the way I outline in the package, use the Crane mechanical springs from the kit, should get you there.

If you have a bit of time, please pull,cap,and rkgkr and find out which weights and center scroll you are using now, they have numbers on them.

So many tuning problems are directly caused by top tuners and dyno hero's doing their very worst, recommending to "rip that vacuum advance off it, it don't do anything, any way", except make the engine run better than they ever could.



 


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