Timing question
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Joined: Apr 2005
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From: webster ny
Timing question
In Lars timing paper he says:
NOTE: This procedure cannot be used on the HEI ignition systems. Removal of the springs will cause an artificially over-advanced condition that will never be achieved with the springs in place. You can use the basic technique described in this paper with the HEI units (setting timing up to 36 degrees), but to check total timing, you must install a set of soft springs. You cannot remove the springs altogether. With the soft springs in place, rev the engine until the centrifugal advance is pegged out. Adjust for 36 degrees total. Then re-install your original springs.
Ok I understand everything he is saying less, the adjustment part. What exactly do you adjust?
If you rotate the distributor, are you not then also changing initial timing as well?
Thats my confusion - I understand (perhaps incorrectly) total timing to be made up of 3 different components - initial timing (set by rotating distributor)
vacuum advance (controlled by engine vacuum, can be adj with aftermarket type)
mechanical advance (controlled by ??? springs??)
So I guess my point is, if I set initial timing to say 16 deg by rotating the distributor as needed (with vacuum advance disabled), and then, I try to set mechanical advance to 36 deg at 2500 by rotating the distributor.... the two adjustments will interfere with each other.
Thanks,
Hef
NOTE: This procedure cannot be used on the HEI ignition systems. Removal of the springs will cause an artificially over-advanced condition that will never be achieved with the springs in place. You can use the basic technique described in this paper with the HEI units (setting timing up to 36 degrees), but to check total timing, you must install a set of soft springs. You cannot remove the springs altogether. With the soft springs in place, rev the engine until the centrifugal advance is pegged out. Adjust for 36 degrees total. Then re-install your original springs.
Ok I understand everything he is saying less, the adjustment part. What exactly do you adjust?
If you rotate the distributor, are you not then also changing initial timing as well?
Thats my confusion - I understand (perhaps incorrectly) total timing to be made up of 3 different components - initial timing (set by rotating distributor)
vacuum advance (controlled by engine vacuum, can be adj with aftermarket type)
mechanical advance (controlled by ??? springs??)
So I guess my point is, if I set initial timing to say 16 deg by rotating the distributor as needed (with vacuum advance disabled), and then, I try to set mechanical advance to 36 deg at 2500 by rotating the distributor.... the two adjustments will interfere with each other.
Thanks,
Hef
Team Owner
Joined: Jul 2001
Posts: 182,997
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From: Lakeland, FL
Cruise-In IV-V-VI-VII-VIII Veteran
St. Jude Donor '03, '06, '17
I never worry about initial timing.. I just set my timing to 36 degrees total.. It doesn't matter to me what the initial timing is as long as I get my 36 degrees total 
Tech Contributor
Joined: Aug 1999
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From: At my Bar drinking and wrenching in Lafayette Colorado
Hef -
You are correct. When you set up for total timing (which does not include vacuum advance), you are also changing initial timing. The two are tied together by the length of the timing curve. The only way to separate the two is to alter the length of the curve. In most cases this is not necessary, as initial timing is irrelevant for performance. As long as initial timing falls somewhere in the range of 12-20 degrees, you're in pretty good shape. You can then add more initial timing for idle quality purposes by running your vacuum advance off of manifold vacuum if you'd like. If the car does not want more initial timing, you can run ported vacuum. But it's total timing that is of interest and most important. Olivier is correct.
You are correct. When you set up for total timing (which does not include vacuum advance), you are also changing initial timing. The two are tied together by the length of the timing curve. The only way to separate the two is to alter the length of the curve. In most cases this is not necessary, as initial timing is irrelevant for performance. As long as initial timing falls somewhere in the range of 12-20 degrees, you're in pretty good shape. You can then add more initial timing for idle quality purposes by running your vacuum advance off of manifold vacuum if you'd like. If the car does not want more initial timing, you can run ported vacuum. But it's total timing that is of interest and most important. Olivier is correct.
