[serialk11r]

Hey guys, when I was thinking about how a positive displacement pump would work as an "air motor", I realized that an important part of the equation is intake plenum volume and acoustics...If the intake plenum volume is very small compared to the displacement of the engine, then most of the losses for an underdriven Roots blower are eliminated as the piston more or less directly does work on the rotors.

Then I realized that ITB setups have an extremely small distance from the throttle to the cylinder...and thus a very low volume between the throttle body and the cylinder! Moreover, since you're flowing a smaller net quantity of air through each throttle the throttle plate should be closed more. Then each piston will draw a slightly deeper vacuum during the intake stroke, with less adiabatic free expansion going on at the throttle body. After the intake valve closes the air pressure after the throttle will start to equalize with the air before the throttle, but since the volume of low pressure air is smaller, the free expansion loss should be lower.

Of course, getting ITBs solely for this purpose would probably be stupid since I can't imagine the difference being very big, but I wonder if anyone's bothered to document this...