Thats quite interesting in the % drivetrain loss dept actually....

636rwhp/3800 = 864fly to run the no's
60 Foot E.T. : 1.33
1/8 Mile E.T. : 6.02
1/8 Mile Trap Speed : 112.88
1/4 Mile E.T. : 9.54
1/4 Mile Trap Speed : 140
36% loss on the day at the track to rwhp dyno figs

508rwhp/3700 = 650fly to run the no's.
60 Foot E.T. : 1.45
1/8 Mile E.T. : 6.56
1/8 Mile Trap Speed : 103.58
1/4 Mile E.T. : 10.40
1/4 Mile Trap Speed : 129
28% loss per rwhp dyno figs
thats a bit excessive in the loss dept!
perhaps weight is the answer if drivetrain the same?

As I said before I'm not saying my calcs are 100% as only a tool but its worked out pretty much spot on for everything I've ever inputed, but then it would cos I'm after hp no's for the cars I ran and know about all the spec of the motors which matches up with hp produced/weights and timeslips + I ran at the same track every time, Santa Pod. 0 elevation....so you just keep changing the hp no. till you get the Actual ET/mph run....working in reverse if you like.