Ok, answers: pump gas, Dyno is an eddy current dyno - proven in the past to be pretty accurate,(religious maintenance, calibrations, resetting baro/temp/etc. for every run among other things).
The throttle body is a LS2 electronic one - GTO/Corvette style. Intake is the Samberg radiator setup.
Where is the power? I think two things - one, shaved heads giving about 11.4:1 compression ratio,(vs about 10.4:1 on unmilled L92's), and the camshaft being spec'd properly for my build. The intake - basically a stock LS3 intake, in front of the throttle body - very similar to a Camaro setup - a straight shot.
Honestly - initially we thought something was wrong in the settings for the dyno,(you set the weight/etc..) - it was set for a camaro,(3400 lbs), and when it was reset to 2800lbs, it hardly changed at all. The best non milled/shaved L92 w/LS2 motor he had done before was about 475rwhp. So my extra nearly point of compression, the very straight shot intake and a good exhaust setup are likely the difference. I expected lower than a camaro setup because of a solid axle vs independent rear suspension - bottom line, its one beast of a motor. Took it out for a drive this afternoon with my dad - no traction in 1-3rd, and it starts getting squirmy in 4th....
515 rwhp, 2800lbs - about 5.5 lbs/hp. If you go by flywheel hp,(1.15 correction factor) about 590-600, 4.7 lbs/hp
To put it in perspective - new ZR1: 5.25lb/hp with flywheel of 638 and weight of 3350.
Mclaren F1: 627hp, 2950lb - 4.7lb/hp,(same as mine)
If you've ever watched videos of the McLaren F1 on the track - and the absolutely brutal accel/spinning/etc.., that is very much what my car is like right now.
