[Christ]

Originally Posted by dcb

...and then some (no internal engine friction for large chunks of your trip)

The vacuum pump increases internal friction by forcing the rings to seat under non-combustion conditions... It reduces pumping losses by evacuating pressure from the crankcase, creating a positive pressure differential between the top of the piston and the bottom of the piston, which makes the power stroke "more effective", since the piston doesn't have to displace a mass of fluid (air) in order to reach BDC, nor does it have to fight against the same to reach TDC.

Also, increased ring seal prevents blow-by, so marginally better efficiency is produced due to less pressure loss into the crankcase.

The power loss due to the increase in friction is inevitably over-ruled by the decrease in crankcase pressure, which aides in more efficient production of power.