Cheap Horsepower-Ram air

[Ed Mellinger]

"Ram air" just uses the Dynamic Pressure at the front of the vehicle to
aid engine breathing.  The formula is simple, 1/2 the fluid density
times the velocity squared (in suitable units).   This works out to
about .04 psi boost at 50 mph, .17 psi at 100 mph, and .7 psi at 200
mph; pretty feeble boost (although not as feeble as the
previously-mentioned cooling fan), but what the hey it's nearly free. 

Let's see, top speed goes roughly as the cube of engine power; if 0.7
psi boost gave (.7/14.7) about 5% more power, top speed would go up by
1.6% or the previously mentioned "few mph".  I'm glad that the UJM has
done many good things for motorcycle technology over the years (can you
say 150 street hp per liter!) 'cause this doesn't look like one of 'em.

Getting cool air from in front of the car is much more significant for
street driving; if the radiator exhaust air is 45F warmer that's a 5%
density (power) loss right there.
 
The BMW list has had a sad thread going from a fellow whose 7-series
hydro-locked during a Miami thunderstorm... if you are thinking ram air,
think also about the wall of water that hits you when a semi hits a
puddle in the adjacent lane...

Ed