What would be peculiar to your combo where more boost than say, 6-8lbs or so, doesn’t show up as more power...... compared to other builds, also running non-intercooled roots blowers carbureted on gas, where they still show improvements with higher boost levels than you’re running?

In the pic above........ how is the drive shaft rpm higher than the engine rpm?

68 Satellite, 383 with stock 906’s, 3550lbs, 11.18@123
Dealer for Comp Cams/Indy Heads