initial timing....initial timing...please read the articles....
There are several types of timing that you need to know about. First, there's the initial timing, which is also known as "idle timing", which is where the timing is at an idle without the help of the mechanical weights inside the distributor, and without the vacuum advance hooked-up. Then there's the mechanical advance, which is the advance you get from the weights inside the distributor. As the engine RPM comes-up, it's the initial timing AND the mechanical advance that gives you your TOTAL timing. For instance; say your distributor has 26 degrees of mechanical advance built into the weights inside and you want a total of 36 degrees of total timing; you would need to set the initial timing (idle timing) at 10 degrees (10 degrees on the crank and 26 degrees from the mechanical weights = 36 degrees of total timing).
The trick is; for performance use you want as much advance as you can get on the crank and the least amount from the mechanical weights in the distributor, hence why race distributors have no mechanical advance at all. To really make a trick street set-up you should only have about 10 degrees or so of mechanical advance in the distributor and about 24 - 26 degrees of initial timing on the crank to obtain your total of 34 - 36 degrees of total timing. This will launch you out of the hole much harder, and give you great jack rabbit starts from street light to street light. You NEED advance at low RPM to make that engine pull hard. It'll have MUCH better throttle response, a better idle vacuum signal, and it'll run cooler & cleaner. Unfortunately stock engines & distributors are set-up completely the opposite so they need to be re-curved to fix this problem. This is why some guys can tune an engine and make it run killer (like we do), and other's just can't seem to get their car to get out of its own way.
Now; to find and set the total timing all you need to do is set the dial on your timing light to 36. Now rev your engine up to about 3,500 RPM (to insure that the mechanical weights are fully activated) and watch your timing mark on the harmonic balancer. Now rotate your distributor until the marks line-up at "0" on the crank. When it reads "0", (yet the light is set at 36), you have a total timing of 36 degrees. Make sure you do this with your vacuum advance NOT hooked-up. If you don't run a vacuum advance, then don't do anything, just leave everything as it is and tighten it down and you're good to go. Your engine isn't really at "0" or Top Dead Center. The timing light is offsetting the light beam by 36 degrees, so you should be reading "0" on the crank.
The total advance will change if you replace your distributor or install an advance curve kit, so always check it and KNOW where your timing is at! It's REAL important on more radical engines, especially on high compression / supercharged and/or nitrous engines! One degree off on the timing can mean anywhere fron 20, 30 or even as much as 40 horsepower loss in some engines!
the link to the mopar muscle articles show how to modify the distributor...