for some time now i have been having issues with my 94Z blowing blue smoke out the back when at operating temp, especially under load. only after about a week after starting my new motor the problem began. i first thought the issue was blow by, but removing the intake and seeing oil in all the runners eliminated that, the problem is the intake gaskets are not sealing and oil is being sucked down the intake runners on the heads. I’ve replaced the gaskets probably 4 times now, using felpro and GM LT1 and LT4 gaskets. i've even used rtv around the ports (w/gaskets) as a last resort, still the problem persists. I’ve done a compression check, all cylinders at 190-200psi(10.7CR), plugs are perfect, has been tuned and the car hauls *** all the way the redline at 6.5k with no drivibility issues at all. also the block has not been decked and the heads have not been milled. My question is has anyone else had issues with brand new AFR heads used with stock intake(i used brand new LT4) not sealing around the bottom of the runners? what was the fix? did milling help? could the increased deck thickness of AFR heads to blame?
Dustin

 

What intake do you have? Do you have the casting number?

 

I assume you are talking about a LT4 setup? If so, I had the same problem for years after I swapped to LT4 heads/intake. Couldn't figure it out for the life of me. Whenever I had the intake off I had to go through the PITA of gasket matching a pair of stock LT4 gaskets to my ports.
My problem was solved after I found out GM makes a LT4 "performance" gaskets that required no grinding to match to the ports and I've never had a problem since. Part number is: 12367777. They come one per package and are about ~$15 each from gmpartsdirect.com.
I'd try those and see what happens.
On a side note... just because you have good compression doesn't mean your oil rings are okay.

 

maybe the u have an oil build up in the valvetrain area.... maybe the oil drain off in the heads to the block werent machined corretly. u could have oil building up and getting past the valve stems and into the combustion area. Or your rings were not installed correctly. It is one of these questions....

 

What i'm using is just the LT4 intake for 1996 vettes (12550630). The gaskets i have on now are gm Lt4 gaskets, they are green with a steel center. i don't know if those are the gaskets your refering to, because i can find the reciept for the gaskets i have on there now, but they did come as a pair in the package. but any way i will look at getting those gaskets anyway since i have to replace them any way. i am now 99% sure the gaskets are the problem because i pluged the pcv vent holes in the intake and valve covers, and hooked a vacuum gague to the dipstick and at idle there was no pressure build up and under load there was an inch or two of vacuum. the only thing causing this is obviously engine vacuum sucking from the intake runners.
Thanks for all the help!!

 

found the gaskets described, definatly not the gakets i'm using now, hopefully they will work!!

 

are you not using the LT4 "RACE ONLY" gaskets?

Theres a required gasket just for those afr's