HELP ME with adjustable vacuum advance - Team Camaro Tech
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post #1 of 5 (permalink) Old Feb 2nd, 01, 01:26 PM Thread Starter
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Join Date: Jan 2001
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I just got the crane (I think) adjustable vacuum advance kit with the limiter plate. I put the one blue one silver spring in and followed the directions and I heard a little ticking (I think) so I put the other blue spring in. Then I took it for a test drive and it was better off before I did anything. Now when I accelerate it's a dog. The springs that were in it are heavier than the blue springs.

I got a stock 350, headers, edelbrock intake/carb, TH350. I'm in the mtns also about 6000ft. It's a rebuilt HEI so maybe it has modified weights or springs?

Also when they say lube the dis. weight's pivot points what should I use to lube em? Also should I connect the vacuum advance to the manifold vacuum or ported vacuum. I want the best performance possible but don't we all. I'm not worried about emissions though. If anyone can even point me in the right direction that would be great too.

[This message has been edited by 67stock (edited 02-02-2001).]
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post #2 of 5 (permalink) Old Feb 2nd, 01, 04:42 PM
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Freddie
 
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Tune the car with the vacuum unhooked first. Set the mechanical advance for maximum performance. Start out by adjusting the inital timing at idle for the best throtle response and then set the mechanical advance for about 36 to 38 degrees total. After you have the engine performing at it's best, start setting up the vacuum advance. You want to tune this for fuel economy so it needs to be at about 40 to 42 degrees total. This is with the vacuum line hooked to a ported source. With the line hooked to ported vacuum, the vacuum advance will fall off to nothing under full throtle (mechanical advance only) so you don't run into detonation, but you will have full advance while cruising. If you have any spark knock while setting up the mechanical or vacuum advance, back that one off untill it goes away. I hope this is clear to you. Some things are hard to explain.

------------------
'69 RS/SS396 pro street
427/4spd/9"

[This message has been edited by big gear head (edited 02-02-2001).]
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post #3 of 5 (permalink) Old Feb 2nd, 01, 05:04 PM Thread Starter
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I was just toyin with it and put the original springs back on. It must have different weights cause the stock ones are real stiff and the crane ones that came with the Va. advance (even the heaviest ones) are lighter than these.

How do I know what the mechanical is set at? All I have is some springs doesn't give me anything to work with. I think I'm getting knock on mechanical.

You know can I just go to NAPA or GM and ask for some springs and weights or what?
Also what do I lube the pivot points(for the weights) with?
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post #4 of 5 (permalink) Old Feb 2nd, 01, 06:06 PM
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Freddie
 
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Put some grease on them very lightly. Use your timing light to check the advance. You need to mark your balancer every 10 degrees and mark the 30s every 2 degrees. This way you can bring the RPMs up to about 3500 and see what the advance is doing. The mechanical advance should all be in by 3500. Its a trial and error thing. Try one set of springs and then swap them for another set untill you get it right.

------------------
'69 RS/SS396 pro street
427/4spd/9"
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post #5 of 5 (permalink) Old Feb 2nd, 01, 09:05 PM
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joe
 
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I wrote this to help someone who was trying to set their distribitor up. There are many different ways to do it but here is a copy maybe it will help.

You have two advance systems built into the dist. (vacuum and mechanical) that operate independently of each other. The vacuum canister rotates the plate that the points are screwed down to by using a manifold vacuum operated canister. The vacuum canister has two variables 1) the amount of its travel (rotation of points plate in deg.) and 2) the amount of inches of vacuum (hg) it takes to make it rotate the points plate and thus advance the timing.
Mechanical advance uses weights and springs (centrifugal force) to advance and retard the timing and it also has two variables 1) the amount of rotation travel in deg. (using a pin and slot) and 2) at what speed and rpm it reaches total advance (controlled by spring tension)
One more thing has to be considered - the vacuum source.
Ported vacuum is taken above the throttle valve so there is no vacuum at idle.
Non-ported has vacuum at idle.
Some say ported vacuum is used to improve the emissions by causing higher exhaust gas temp with a retarded spark at idle so some carb books will tell you to use it - some engines may run better with non ported depending on the way the vacuum and mech advance is set up in the distributor.
Now the fun part; you get to play with the 6 variables to tune your engine. 1) ported vacuum, 2) non ported vacuum, 3) amount of vacuum (hg) needed to operate the vac canister, 4) amount of travel of the canister linkage, 5) amount of mach advance travel/rotation (deg) and 6) how soon or late your mach advance comes in (springs)
Now how do you make the adjustments?
A stock canister is fixed - for example a high hp canister may open at 8-hg vacuum.
Some low hp cans open at 15 hg. You can buy an adjustable can with a setscrew in the vacuum nipple. This is needed if you have low vacuum because of a “big” camshaft.
To limit the travel of the canister - you put in a little adjustable plate that adjusts (limits) the travel of the can linkage . The rotation of the mechanical advance is changed by installing a brass bushing on a pin that rides in a slot or by brazing up the slot to shorten it. (It’s under the rotor) How soon your mach. advance comes on is adjusted by swapping the springs.
Now you need the numbers (tricky part) no one can tell you what is best for your combo of engine, trans, rear gear, fuel, and driving conditions.
To get started ( your numbers will differ) first set mechanical advance using timming tape on the harmonic balancer. Some people recommend to set the distributor mechanical travel rotation at 24 deg (fix the pin and slot or use bushing) put in springs that bring in advance by 3500 rpm , set initial at 12 deg. This gives total mach advance of 36 deg. Now limit your vac can travel (the little plate on end of vacuum advance linkage) to 10 deg of advance at full non ported vacuum. Now with vacuum connected to non ported source you have 22 at idle and 46 at 3500 rpm. Using non ported vacuum, the engine will adjust its own vacuum timing as its vacuum changes. It will have no vacuum advance while cranking or at WOT but will advance timing while at low loads for better fuel economy. The mechanical advance will change with the RPMs. You will have to experiment with all 6 variables to get the best numbers for your car or send your distributor to a shop with a distributor machine.


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