If you need guides, valve, seats, etc is better to buy a pair of rebuilt heads than to pay a machine shop to fix yours.

I'm not yet convinced you are doing the testing correctly. But you seem to be pretty firmly convinced.

Best wishes.

 

If I removed the rockers and compressed each cylinder to 100 psi, what could be incorrect about the testing? What other variables could there be? Like I mentioned, maybe my turning the motor slowly by hand made a valve stick? That’s about all I can think of. It’s no small amount of air coming out of the intake.

 

If you have 90+ compression you have very little leakage and not much is coming out. I worry that you are mistaking normal hissing during pressurizing of the cylinders as a problem. Hence the ONLY WAY TO TELL IS TO DO A REAL LEAKDOWN TEST WITH A LEAKDOWN TESTER, NOT WHAT YOU ARE DOING WHEN SIMPLY PRESSURIZING THE CYLINDERS.

I don't want you to pull the heads off unnecessarily. That's a lot of work and head gaskets aren't cheap.

If you really feel that air coming past the intake valve is excessive, then go ahead and pull them. But then again, how did it ever have 90 psi of compression? Hmmmmm - Does it have a broken valve spring? Try pressing down on it and comparing to others. Lots of repairs like this do not require heads to be pulled.