Thread: Low Engine Vacuum

Tweet

Is there anything else that might cause low engine vacuum at idle other than late valve timing, a leak, or a radical cam?

Worn rings? Here's a link to a site I found not long ago - at the bottom there's a set of situations with visual and word descriptions of how the vacuum gauge reacts to problems - How to Use and Interpret a Vacuum Gauge

I'm sorry. I should have stated this is a freshly rebuilt engine. I've got around 500 or so miles on it.

Maybe rings aren't seated yet? Take a look at the link - helped me get a handle on reading the vacuum gauge. Sorry if it wastes your time.

No, it's not a waste of time. I've actually read that before. I built this engine over the winter and got it put in and running back in the spring. It's a 327 small journal, bored .040, flat top pistons. cast iron rings, New PBM Performance Thunder series heads (World Products S/R Castings), 67cc chambers, 2.02/1.60 valves, .039 compressed thickness head gaskets, Edelbrock Performer intake, Quadrajet, stock exhaust manifolds. The cam is a Lunati Bracket Master II, 218 Dur. @ .050, 284 Adv., .458 Lift, 110 ls. I've got a closed L79 PCV system with the valve screwed into the oil filler tube. The motor idles and runs good and the plugs are a nice tan color although they do have a little carbon build up on them. Every compression calculator I've used comes out with 9:1 compression ratio. I wish I would have used a dome top piston instead of flats. I would rather have had 10:1. Anyway, I've got two problems with it right now. (1) It only pulls 10" of vacuum at idle. (2) It's using oil. I've adjusted the air mixture screws for max. vaccum but 10" is all I can get. As far as the oil issue, I had an oil leak I had to fix and for right now it's not leaking. It does not smoke and the tail pipes are not oily, a little sooty, but not oily. I'm wondering if the PCV valve is faulty. I haven't done a compression check yet but I'm going to. I've got to buy a checker. The rings may not be seated good yet but I've got 500 or so miles on it. About half of those miles were on long runs to car shows. Maybe I need to drive it around my neighborhood more and really get on it. I'm running Bradd Penn 10W/30 oil right now but I'm thinking of going to 10W/40 or straight 30W. Any suggestions or like experiences?

I pulled the hose off the PCV valve, stuck my pinky in it and it has fresh oil in it. So, I guess I should try another valve. Could this also cause low vacuum?

The pcv will pull oil out of the pan because the dipstick tube extends down into the pan about 3 inches into the oil--