Hi All, I have a 1974 400 cid in a 67 chevelle. It seems to be building up too much vacumm pressure in the block. When I take the oil filler cap off the engine races up a bit. Put the cap back on and it starts to build up again. Its starting to push oil past the timing cover, oil dip stick, ect. Not good. We have checked everything we can think of. It has an Edlebrock performer intake with an edlebrock carb.
We are wondering if may be too much or wrong for the block or if its the intake / carb combination some how causing this.
This was built for street use so its got a mild cam, ect.

Any ideas are welcome. Thanks

Ed  

sorry I ment positve pressure not vacuum pressure  

That is a sure sign of significant blowby.  

Are you running any sort of a PCV system on the motor?