What surprised me a little bit was I saw 2.15 inches of
water or about .08 psi on the back side of the rad. This means
there is a lot of excess cooling to be had from this rad at high
speeds if somehow the pressure could be lowered behind the rad.

With a properly vented cowl the first gen RX7 rad with metal
header tanks might work fine for our purposes. This however points
up the extreme importance of getting the air out from under the hood
and out of the cowl for that matter. It is absolutely essential that
you make these pressure measurements or you are just spinning
your wheels trying to cool your engine.  There is no way of knowing
what is going on unless you make these pressure measurements.
The sad part about it is nobody does it and it is real easy
to do if you know how.

Paul:  Have you tried this with the hood propped open at the rear a bit, to
let out the air?  Back in the 70's and 80's a lot of guys with 'Vettes used
that trick to help cooling.

I would be interested to know the effects of letting out the air...

Al.

Sure did Al. You missed the message apparently.

Subject:        More pressure measurements
   Date:        Sat, 09 Feb 2002 00:46:24 -0800
  From:        ACRE NL <rotaryeng@earthlink.net>

Did some more pressure measurements on the first gen RX7
today. Since the pressure in the cowl was high
I thought I would try opening the cowl flaps.

No luck. Only a minor improvement in under hood pressure.
3.7" H2o in front of the rad 2.7' H2o behind the rad and
1.8" H2o on the firewall. Essentially the same as it was with the
hood closed. I surmise the reason for this is the pressure
at the base of the windshield is real high. Air is going in
the engine compartment from the base of the windshield and not
out as one would think.  We shall see with the next test.

Paul Lamar

Paul,
Perspective from a non-engineer...

I can't help but think that you would see an better results by increasing
the length of your 2x4 to extend all the way across the windshield area,
thereby blocking the high pressure air from entering the engine bay due to
the high pressure area in front of the windshield.  Seems that this would
result in the underhood air being drawn out along both sides of the
hood.  Yes... No?
Mark Steitle

You are probably right Mark. I just did not want to spend too much
time on it and I had that 2 x 4 lying around. I had no intentions
of cutting holes in the RX7. Any effective holes would probably require 
a lip at the front edge and a streamlined outlet. This was mainly a 
demonstration exercise for people doing cooling development work on 
their aircraft.

Paul Lamar
 
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