How many horsepower do you suppose it requires to turn, say, a 200hp engine at 2000rpm? Lots.
If you extend the best-economy plot in
this diagram (a 250HP engine) all the way down to zero fuel, the intercept on the power output axis is somewhere around
minus 60HP which I think represents the friction losses at ~ 2000rpm.
I hope I got that right.
It is about 25% of max rated power.