Running Non-CC Hei W/o Vacuum Advance

[PeteA216]

Hey guys,
I want to play around a little bit and experiment. If I wanted to run my non-CC HEI distributor without it's vacuum advance like so many others do, relying solely on the centrifugal spring & weight advance, how would I go about setting the static timing? I know normally, whil ate idle at or below 800 RPM (depending on the centrifugal advance setup) you unplug the vacuum advance and plug the hole in the carb to prevent vacuum leaks, causing the canster drops down to minimum advance. You set it (8 degrees BTDC usually) and then plug the vacuum advance back into the carb and vacuum pulls it to full advance while the centrifugal weights are at minimum advance. Without the vacuum canister hooked up, at idle (or any time) it won't be pulled to maximum advance so how should the timing be set to compensate? My timing plate only goes 8 degrees both ways. I see this done all the time, but don't know how they do it. Any help would be greatly appreciated!

[SpinnerCee]

Advanced vacuum advance at idle is a fuel economy crutch for low-compression engines -- your hi compression performance engine will not like it at all.

Leave the vacuum advance disconnected and plugged.

Too much advance will melt your pistons -- unless you are using race gas with more than 100 octane, 8 degrees of initial timing is all you need.

[Blue Bowtie]

I can program in an advance curve with your EST distributor which would be impossible with any combination of weights, springs, advance cam plate, and a dual vacuum advance/retard unit. If this is in your '84 B-Car, and is basically a stock engine (less than 290º lobe duration and less than 11:1 static CR) you'll be doing yourself a disservice by switching to a mechanical distributor.

[PeteA216]

If this is in your '84 B-Car, and is basically a stock engine (less than 290º lobe duration and less than 11:1 static CR) you'll be doing yourself a disservice by switching to a mechanical distributor.

Yeah, this is on the Caprice. The ECM has long been removed from the car though. Under the hood resembles that of any pre-CC car. The engine is from a '69 Camaro according to the casting number, which is the only reason I find myself posting in the classic forums.

I did try to run it without the vacuum advance, and advanced the timing to 8 Degrees BTDC and what a difference! After driving it and advancing, over and over I was able to get roughly 11 degrees BTDC with no engine ping, but a whole lot of power.

[SpinnerCee]

Told ya

The next thing you want to try is to find a vacuum port above the throttle plates on the carb to hook the vacuum advance into -- it should be easy to find, since the manifold ports are almost always IN the carb basplate, so just about any other ports you find can be assumed to be above the carb's throttle blades. It's also likely to have a cap on it, and when it's open with the engine running, you should feel very little or no vacuum. Try it without changing your base timing, then make the timing and idle adjustments to compensate, if you need to retard the base timing to less than 8 degrees, plug it and go without it.