Injector scoop: aerodynamic drag

I've often wondered if there has been a systematic study of the trade-off between the aerodynamic drag of the injector scoop and the extra horsepower it may provide. This only becomes an issue when the car is really moving -- the aero drag scales nonlinearly with velocity, but I can't guess how much extra horsepower ram-air induction provides at 200, 220, or 250 mph. Is it enough to overcome the extra drag it introduces?

I'm no aerospace engineer, but my hunch is it would be better to get the scoop out of the turbulent airstream. The air has to make an abrupt right angle turn into the supercharger, presenting all kinds of flow uniformity problems that dynamically change as the car picks up speed. Does the supercharger not care? Have dyno tests ever been performed with air blasting into the supercharger scoop?

Why not pick up the air from a `quieter' area of the vehicle? This would lead to more controlled and hence more reliable power from the motor because the supercharger would not be dealing with all that turbulence at the input. Plus it looks to me like the scoop represents a significant portion of the frontal cross section on a TAD, and a very lossy one at that. The position of the injector scoop on most FC's appears to severely break up the flow of air across the hood, resulting in additional turbulent drag.

I'm sure this question has been kicked around for probably four decades. I know there is extensive wind tunnel data, but I doubt the motor is running during these tests. I'd be interested to hear the current thinking.

 

more on injector scoops

We did an article for IHRA on the relationship between the engine air consumption, vehicle speed, and cross-sectional area of the scoop. You can down load it from "ARTICLES" in our web site:
www.racecarbook.com
Bob Szabo, Author of Fuel Injection Racing Secrets & 5000 Horsepower on Methanol
bob@racecarbook.com