I puzzled over these numbers as well. The chassis dyne is going to be a measurement of dyno drum torque and 750 lb-ft is meaningless without also knowing the drive wheel diameter and the dyno traction drum diameter and having verification of the rearend ratio.
I have done work on chassis dynes for transmission test stands for Borg Warner and if there is anything the big auto makers are (in)famous for it is specsmanship.
Lets say the dyno rollers are 16 inches in diameter and truck tires are 32 inches (easier math :p )
That means that 750 lb-ft at the drum is 1500 lb-ft at the rear wheel / 3.73 = 402 lb-ft at the flywheel. My experience tells me that most drivetrains of this type are actually much higher than 95 - 97 percent efficient which in the worst case would be 402/.95 ~= 425 lb-ft of real torque at the flywheel.
That sounds about right . . . if the dyno drums were smaller, that would mean higher engine torque. I bet the drums are smaller than 16 inches, I have seen them between 12 inches and 14 inches most commonly which would equate to something a bit closer to 500 lb-ft at the flywheel.
zatmakesense?
