Antz81

What should a stock (except for removed AIR, EGR, EFE, with long tube headers and dual exhaust, no cat) have for the manifold vacuum at idle? Currently I'm getting 16", but think this should be higher. (my brothers 82 silverado gets 19") I'm not completely certain on my cam but I do believe it is the stock cam.

7T1vette

If the engine has lots of miles/wear and you still have the stock cam in it, you should be getting anywhere from 18"Hg to 20"Hg. To determine the max vacuum your car can produce, you need to disconnect and block-off ALL manifold vacuum sources from the engine and THEN check it. If you get a lot more vacuum, you will have one or more leaks to find and repair. Just add stuff back one-at-a-time and identify the system[s] that cause the leakages. Then chase them through that line until you identify it.

Antz81

I've disconnected everything but the brake booster (which i am 100% sure is not leaking) and still get the same. The engine idles fine and doesn't seem to be lacking in power. I've had a thorough check for vacuum leaks, but can't find any.

SH-60B

You can experiment with the ignition timing in search of higher vacuum.

Antz81

I've checked with 6, 8, and 12* initial timing, all give the same result. Currently I'm on 12* for the small performance gain.

Antz81

Vette is a 1981 4 speed. I thought I had this in the 1st post

MelWff

what rpm when you get the 16" reading?

Antz81

700rpm

MelWff

You unplugged the computer connection at the distributor and the vacuum line before setting the timing to 12 degrees initial?

Antz81

EST connector on the distributor was unplugged. No vacuum line for timing on an 81