Texasdoc Can you get us a couple of pictures of the motor? It sound like you have done your home work with installing the stroker kit. I got a kit from Brent and did he same sizing and everything to install the kit. I got 484 cubes of rotating mass and run tall valve covers to clear the Erson setup. There are shields inside both covers. The R/S valve has my pcv going to the main port at the base of the throttle body and have a Cheap Cal custom breather on the other side. I had it the other way and was sucking oil through the motor when racing. Went to the other way and no problems. I don't see how there is any way with both a vacuum source and open breather can cause a pressure buildup inside the motor. We need to get a gauge on this and check the internal pressure when driving.
If a head gasket breaks, you get coolant high temps and smoking 90% of the times out exhaust. Oil leaks speak for them selves, rtv, gasket failure, seal cut, simple to find and repair.
Is it possible the the block is warpped? When cold it seals and hot it leaks? The last thing would be a cracked head. Have to be on the exhaust side and blowing a small amount of pressure back into the motor through a bad valve stem or port crack.
Piston rings do flutter when the motor is running, the chance of a couple of cylinders getting end gap to line up is like winning the lottery but if the leak test show air getting into the bottom of the motor, we have an issue. The other idea is that the cylinders are not round and would need to measure both taper and out of round. The head studs or bolts may have distorted the cylinder walls and the rings are not staying flush. As the motor expands from heating up the clearance grows up to .001" This is not alot but for gas to escape, it doesn't need much.
Here the thing, and this would get you through the summer without chasing this leak, add a vacuum pump with a low output of 3-5 psi and seal the system. Car the car for the summer and in the winter or down time pull the motor and have it done over by a pro machinist. That pump will not hurt anything at low pressure and keep the motor sealed without leaks.
Other choice is a tank and lines hooked to both valve cover and run 2 small filters on top. Have the pcv valve working. I see no way for this block to build up pressure. You do need a drain to return the oil back to the motor.
And the fight goes on. We will get it. Rick L.
Pictues of the motor
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