Panther -

About 23 psi @ WOT which is probably near the upper limit of where I want to be.

All -

Assuming I will need to pull the intake manifold and replace the gasket, does anyone have a recommendation on the best BBC (502) intake gasket (brand, p/n)?

either merc or felpro W/ aviation permatex

1274 Fel-pro

Check the intake bolts 1st before you do anything to either confirm or eliminate the intake not tight allowing water to blow past the intake gaskets. While I was chasing down my problem, the gaskets always looked good with no signs of leakage. I probably could have just tighten the bolts down and been good to go, then replace the gaskets once the problem was found.

Are your water passages corroded on the intake gasket surface on the intake?

What is the end gap at the front and rear of the intake manifold, ck both sides with a feeler gage to make sure you have clearance and the intake is fitted correctly.

Try pressurizing the system ? It will eliminate reversion possibility. Last spring a friend of mine put 2 brand new intakes without checking the gap around the water passages. When I removed the int manifold it was clear to see the gasket had more crush on the the top than the bottom. The other side was just fine.
Had a problem a few years back & replaced the risers with Sierra's. Turned out it was the design of the piece of S**T aftermarlet risers. Replaced with merc's & solved the problem.

Oil temp? how are you venting the valve covers?

What intake are you using ? Also intercoolers are known to leak. I like the Cometic gaskets. But the felpro 1275's work well for me. What temp. is the motor running at, this could be a dead giveaway to the problem. BBB

Heads shaved, block deck shaved? You may have incorrect geometry causing poor intake to head sealing. I've seen this happen before.

Thanks for the part numbers.

I'm running the Whipple supplied intake manifold. The setup uses a crossover so my water temps rarely get over 100°F when I am running.

Oil temps spend most of their time warming up to 180°F, then peak at 190-200 for short bursts when I finally get to open it up. My valve covers are vented with a single small breather over the starboard cylinders, and a PCV valve on the port side.
Is there a chance that this is condensation? The oil was pretty crappy. How many boat trips in colder weather does it take to turn oil into chocolate milk?

It sounds like I may eventually have to pull the intake and have a look. In the meantime, I will probably figure out a way to pressure test the block. Anybody done this before? What do I need?

As I mentioned before, I did find a few loose bolts on the intake the last time I had the intercooler off. Unfortunately, some of the intake bolts on the Whipple setup are actually in the plenum area so you have to remove the intercooler to get to them. I'll still check the torque on them before taking them out.