I have yet another question concerning initial and total mechanical enging timing. I have read the various message threads and from what I can gather you would want 36deg timing in by 3000 rpm with approximately 16 deg initial timing and 20 degress of advance, but I am not sure if this is applicible for big blocks or small blocks so I need to ask the question once again.

My configuration:
'69 Chevelle SS coupe
M-21
3.73: Differential
325 hp 396
2-bolt main
bored .30 over
Keith Black hypereutectic poston
cast iron exhaust manifolds
Edlebrock torker 2 manifold
Comp Cams high energy hydraulic cam 218/218
Comp Cams roller tip rockers
stock oval port heads with 3-angle grind
Mallory unlite distributor
Jet stage 2 quadrajet
Centerforce 2 clutch

Thanks

Do you know what the compression ratio is? if it's stock CR, you have iron heads and a short cam, you might be pinging pretty bad with that timing. see if you can get a setup like 12 + 20 + 10 or 15 vacuum advance. Most of the newer MSD HEI type distributors will be able to produce those figures. A stock distributor will have to be modified by somebody who knows what he's doing to get that curve.

Do you know what the compression ratio is? if it's stock CR, you have iron heads and a short cam, you might be pinging pretty bad with that timing. see if you can get a setup like 12 + 20 + 10 or 15 vacuum advance. Most of the newer MSD HEI type distributors will be able to produce those figures. A stock distributor will have to be modified by somebody who knows what he's doing to get that curve.


Make that manifold vacuum too. Not ported. You want the vacuum advance to go away when you step on the throttle.

what do you think happens to ported vacuum when you stomp on it?

each engine is different.
if you build 2 identical engines, and put one in a heavy car with highway gears and an automatic trans and the other in a light car with deep gears and a manual trans, you will need a different setup on each.
just play with your timing on your car and see what it likes.

In general, I prefer less initial and more centrifugal with a stock or mild cam. Too much initial advance with a stock cam makes it very hard to get the idle speed low enough.

More initial and less centrifugal with a radical, poor-idling cam. Extra advance means you may be able to idle the engine with the idle speed screw somewhere near stock position; keeps the throttle plates where they need to be in relation to the transfer slots in the carb.

"Slow" advance in a heavy car. (all in at 3000 rpm or thereabouts) In a REALLY heavy vehicle, or with very low-number "highway" gears, you may need to go to an even higher RPM to prevent ping.
"Fast" advance in a light car, or with very high numbered gears (all in at lower RPM)

As much vacuum advance as the engine will tolerate without any ping at part-throttle--including when accelerating at part throttle.
Ported or manifold vacuum; whichever one you like best. Try 'em both.

what do you think happens to ported vacuum when you stomp on it?

As engine rpm increases vacuum signal to the vacuum advance increases, virtually instaneously. If he is having pinging problems increasing the signal to his vacuum advance is exactly what he DOESN'T want.

Beyond that I suggest you hook up a vacuum gauge to a ported vacuum source and blip the throttle.

For comparison sake , then , hook that same gauge up to a manifold vacuum source and blip the throttle again. Observe the vacuum gauge's response.

Then come back here and tell us what you saw. :)