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63chev2drht
08-31-2003, 09:14 AM
hello,
I have the Hei. setup in a car I picked up it's a 327/403hp it has a .03/.03 solid cam set at 3degs adv. on the run sheet the timing read like this 14degs.at idle ,31degs at 2500 no vac. and 51degs with vac hooked up can anyone tell me what is going on here.

thanks worked up

msdtech1
08-31-2003, 08:14 PM
With no load on the engine an vacuum applied to the vacuum advance canister, your vacuum advance will be added to whatever your timing is at. An example of a typical MSD Distributor setup would be as follows. Intitial timing set at 12 degrees. Mechanical timing set at 21 degrees. Vacuum Advance at 16 degrees. This would be with two blue springs installed.

Checking the timing at idle.
Without Vacuum - 12 degrees initial = 12 degrees indicated by timing light.
With Vacuum - 12 degrees initial + 16 degrees vacuum = 28 degrees total indicated by timing light.

Checking at 3000 rpm.
Without Vacuum - 12 degrees initial + 21 degrees mechanical = 33 degrees indicated by timing light.
With Vacuum = 12 degrees initial + 21 degrees mechanical + 16 degrees vacuum = 49 degrees indicated by timing light.

Please note that when you put a load on the engine the vacuum is reduced or goes away. Therefore the vacuum advance is only present when the engine is a low speed or while idling.

MSD Tech1