well, I found 2 psi. The nice thing (for me) about getting older is that I can laugh at myself now. In my younger days I'd never post on a board about some stupid thing I'd done.
I built a plug and test fitting to pressurize the intake manifold. Hooked it up to 25 psi and found a big leak. In the throttle body there was (what I thought) a blind hole out the passenger side. I'd looked at it when I installed it, and it didn't go anywhere. Well, it does, goes out in front of the throttle blade. Not under vacuum, but a direct leak under boost. Thing is, you look straight at it and it looks like a blind hole; change the angle and you can just see a passage on the bottom side joining it. I tapped it for 1/8" NPT as you see here:
That now gets me to 12 psi at the intake. I can also hear some slight leakage at the intake o-rings. Very small amount, but who knows how much that may add up to total. Trying to find a stock LS2 intake to try. Don't want to spend a ton of money as I'll never use it permanently, but it will bolt right on and fit my 90mm throttle body. It's also what I had on this engine in the GTO, and had no boost leakage. If someone has one let me know.
Jody