Ram air box truths (real PSI gain)
Gentlemen,
This issue has been explored and many of us have spent hundreds of

dollars

or many hours to install a RAM air box in our aircraft to gain an

expected

increase in performance. Truth be told, there isn't much gain under

200

mph. At least not enough to even register on the airspeed indicator.

I'll

explain why and you can decide for yourself.  This is probably why

no

one

will quote any increase in speed when you purchase a RAM airbox from

them,

because there won't be any.
Here are the true hard facts using the following criteria:

(Publication:

Aerodynamics and Flight)
At   MSL Pressure 14.7 psi  (densest air possible on the planet)
At   200 MPH (if your plane will go this fast) direct air flow (non
obstructed, perfect flow)
At   59.02 degrees F  (15 degrees C)  Standard aeronautical

calculation

temp at MSL

TOTAL INCREASE IN PRESSURE =  0.710 psi

By the way, any performance increase is assuming that there are zero

bends,

curves, voids, filters elements or any other disturbance/blockage of

the

flow into the cylinder head ports. And we all know that isn't the

case

in

our aircraft or engine induction design.  Now, go ahead and factor

in

actual conditions and temp at 2000 to 8000 ft MSL along with your

actual

airspeed (indicated pressure) and the fact that you are not getting
true/undisturbed RAM air into your PERFORMANCE DESIGNED Lycoming

induction system.

You might see 1.5 HP at 2900 RPM's on an 0-320 engine running Wide
open Throttle.  Just don't pack a lunch before flight, you'll get

the

same

results.
Just passing along mathematical facts.

This guy betrays his own lack of 'mathmatical facts'.  Since engine HP is
almost directly related to available manifold pressure, the HP increase
using HIS numbers would be 7.727 HP.  (.710 / 14.7 =  4.829%   * 160 HP =
7.727)

Ever seen a formula 1 racer NOT use a ram air inlet?

Tracy Crook
tcrook@rotaryaviation.com
www.rotaryaviation.com

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