How far do you advance your timing? - Pontiac GTO Forum
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post #1 of 7 (permalink) Old 10-20-2012, 11:51 PM Thread Starter
 
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How far do you advance your timing?

I set my timing at 6 degrees before TDC and it sounds good when at idle but does not accelerate well

I have:
1971 455 block bored .30 over
"96" heads professional built by Butler Performance with roller rockers (details below)
-Competition 3 angle valve job
-FULL bronze guides (not liners)
-Ferrea Stainless Steel valves
-Surfaced on all 3 sides
-Retainers & HD valve locks
-Tall dual springs
-New 5/16 guide plates
-7/16 rocker arm studs
-HP valve seals
-Blue printed and assembled
COMP Cams Magnum Double Roller Timing Set
COMP Cams Xtreme Energy Cam and Lifter Kit PN 223
Pioneer Street Performance Harmonic Balancer
Edelbrock Performer RPM Intake Manifold
Edelbrock Performer Carburetor
PerTronix Flame-Thrower III Ignition Coil
PerTronix Ignitor III Solid-State Ignition System
Hooker competition headers

Thanks for the input,

Joe
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post #2 of 7 (permalink) Old 10-21-2012, 12:43 AM
 
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In general, 6 degrees is probably not enough initial timing. Mine runs best with initial set at 12 (14 with real good gas) degrees before. Total timing is what you're looking for and it determines how your car runs and accelerates. It is a function of your initial timing plus your vacuum advance plus your mechanical (centrifugal) advance and should be somewhere in the 34-36 degree range, plus you want it all in at a certain RPM (generally somewhere around 3000 RPMs or slightly less) depending on your gearing, your cam, and other things.

Lars (who posts here) has a great technical paper that he shares, which tells you exactly how to set your timing.

When the only tool in your toolbox is a hammer, you tend to see every problem as a nail.

Last edited by chuckha62; 10-21-2012 at 10:07 AM.
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post #3 of 7 (permalink) Old 10-21-2012, 01:28 AM
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What you want to do is to set TOTAL ignition timing to the "happy place" for your engine and then just let the initial value land whereever it lands. With iron open chamber heads, "most" Pontiacs tend to be happy somewhere around 35-36 degrees total. Aluminum heads, and also closed chamber 670's, tend to like more than that. If you want to really dial it in, then the process is to start lower - say around 33 degrees - then sneak up on it a little at a time, testing with clocks, until you find the setting that results in the lowest E.T.

To check total advance you'll need either a light that has that capability, or a timing tape on your balancer that has degree readings up to at least 40 degrees. Disconnect the vacuum advance, plug the line, and take the rpm up to where you can tell all the advance is "in" (the marks stop moving under the light) - usually somewhere around 3000 rpm is enough. Once you figure out where your engine likes to be, then take your light and check where it is at idle (like you'd "normally" check timing). Don't change it, just look at it - that way you'll know where to set it in the future without having to work on it at RPM.

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post #4 of 7 (permalink) Old 10-21-2012, 11:02 AM Thread Starter
 
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Bear,

Thanks for the info. If I'm reading this correctly, I want 32-36 degrees before TDC at 3,000 RPMs to set my timing. I will have to play with the engine to find out were it wants to be in the 32-36 degree, then annotate the advance at idle for future reference.

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post #5 of 7 (permalink) Old 10-22-2012, 12:51 PM
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Quote:
Originally Posted by joesweeting View Post
Bear,

Thanks for the info. If I'm reading this correctly, I want 32-36 degrees before TDC at 3,000 RPMs to set my timing. I will have to play with the engine to find out were it wants to be in the 32-36 degree, then annotate the advance at idle for future reference.
Yep, you've got it right.

Bear

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post #6 of 7 (permalink) Old 10-22-2012, 05:46 PM Thread Starter
 
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Thanks again

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post #7 of 7 (permalink) Old 10-28-2012, 12:03 PM
 
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Quote:
Originally Posted by joesweeting View Post
If I'm reading this correctly, I want 32-36 degrees before TDC at 3,000 RPMs to set my timing. I will have to play with the engine to find out were it wants to be in the 32-36 degree, then annotate the advance at idle for future reference.
If you have a stock distributor with the factory springs, chances are good that the total timing won't be "all-in" by 3000 rpm. You want to set the total timing at the point where the centrifugal timing is "max'ed out", whether this be at 3000 or 4000, or wherever it's "pegged out." For optimum performance, you want this to be at about 2500 - 3000 rpm, but you'll have to do a spring swap for that to occur, in most cases.

As Chuck noted, I have a step-by-step paper outlining how to set up the total timing and how to correct the length of the timing curve to obtain the desired initial setting. Just drop me an e-mail request for a copy.

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