ok, bear with me. I'm trying to figure out throttling losses.
Assume atmosphere is 14.7 psi.
Assume 5 psi absolute at idle (guess!) inside the intake manifold.
Assume size of engine is 200 cubic inches.
Assume 1000 rpm.
from here
Horsepower required to Compress Air
it shows .05 horsepower for one cubic foot per minute.
One cubic foot is 1728 cubic inches.
so, we have
.05 hp * 1000 rpm * 228 cubic inches / 1728
is 6.5 horsepower. Which passes the big picture bs test.
Interesting is the fact that a 100 cubic inch engine takes half the power - smaller engines burn less gas at idle.
Duh.