I got my rebuilt engine in the truck last weekend. Fired it up, adjusted idle and timing. It runs, but has about 14" of vacuum at a not very smooth idle. Vacuum is steady. I put a 240 head on it with Chevy rockers. It has an Edelbrock one barrel intake and fuel injected exhaust manifolds. Will the vacuum get better once the rings seat or are the rocker arms the culprit? Anyone running Chevy rockers have any advice for me? Thanks, Tim

 

Engine manifold vacuum of a given engine type depends on a few factors. Camshaft selection being one, a rumpety performance type for example is going to exhibit low vacuum at idle because of things like valve overlap. They are designed for high RPM applications. A stock-ish engine though, in good tune and mechanical condition should pull 18" to 20" Hg at Sea Level. Your tag sez you're in Missouruh, so no high altitude correction factor applies there.

It would not be unusual for a rebuild to show lower average vacuum until the rings are properly seated. This is one reason why it's so important to get a new engine under load and workin' hard right away, excessive idling with no loading on the rings will cause the cylinders to glaze over and they will never seat properly, "oil burner" etc.

Get on the highway, get it hot and (for maintenance test purposes only natch) with some "spirited" driving to include both deceleration and full throttle acceleration. Shouldn't take too long with cast iron rings and numbers should come up.