most 4wd's will see 27-33 % losses, as sed above.
but i have heard ava rollers, 4wd cars only loss 17%, and the operator says, transmission can not lose 100 bhp, cos it would over heat.
the point is
on rollers, or hub dyno's, bhp is measured at the wheels/hubs
and calculated at fly(guessing game).
on engine dyno's, bhp is measure at fly, but you will also loss about 30 bhp once fitted in car, cos of drag of the alternator,power steerin, and even more if air con turned on. then - transmission loss.