I know I have seen on here many times that with an auto, losses to the rear wheels is approx. 20% and I think a manual was about 10-15%. Is there another number out there for actual losses? When you compare a 300 crank hp engine and a 600 crank hp engine using the 20% of course it doesn't add up if both are using the same rear and tranny. Has anyone had their engine dynoed and then a chassi dyno done?

Just curious is all

Losses through gears are proportional to the power through it, so you still have more loss with higher HP. It isn't a "fixed" number. Things like a water pump of course is a fixed loss at a given RPM.

I have found that a "decent" estimate for an automatic car to be about 100 hp through the drivetrain. Manuals are about 75 due to clutch lockup.