Got a 91 Z28 with the 305. Engine got rebuilt but then sat for 4 years. I got it firing up and saw smoke by valve covers. I assume its blow bye so I gave it a compression check and it's around 80. I know it needs to be higher. I think that the rings are not set all the way. Is there any fix or anything to help me besides doing a rebuild?

 

May just need to run it longer. Sometimes squirting oil into the cylinders and leave it set for a while helps.

 

Yes, the basic rule of thumb is to squirt some heavier weight oil into the cylinder through the spark plug hole before inserting the compression gauge and turning the engine over several times.
If the compression rises, the leak is by the rings, i.e. blowby.
If the compression doesn't change, it's likely valves leaking (which is easier to fix).

The engine should be at its operating temperature for the compression check. Though, cold compression of 80psi is way too low, that's a given. I once was offered a freshly "rebuilt" engine with 50psi cold compression. They haven't seen my run so fast before! :-D I got 150psi cold now on my own build. Can't complain!

Let us know what you find.
Lou

P.S.: A stupid question comes to mind: has the engine been ever run after assembly? Or was it the first time now?
And an interesting question: did you just rebuild it to stock specs or did you make improvements? I'd be curious to know what you've done to it, if anything.