[DanielDudley]

Maybe we should, for the purposes of discussion, assume that the losses are 15% at max power, which is the only part of the equation that ever gets addressed.

Perhaps they are less when running at 10% power, and perhaps they are more. Most people are only interested in what total HP numbers they can infer at max output.

Of course a lot of guys only quote wheel horsepower for accuracy. but I am still going to say that drive train losses are related to load on the system, and they would be much less in a no load situation, and much more reflective of what you are saying. If we are talking about a 75 HP loss at 4 or 500 HP, I can only say that that must reflect real world conditions, as engine builders and dyno operators always seem to quote the same loss figures. FWIW, they quote higher figures for AWD vehicles and fuel economy also drops, so I expect the losses are real, whether it has to do with friction or inertial losses or whatever.

They say it is mathematically impossible for bumble bees to fly, but they do anyway, so it must be real. Driveline losses at WOT are the same, for whatever the cause.