I set up my water manometer in the 1st gen RX7
to see what was going one with the rad and the under hood
pressure. I was surprise to see so much pressure under the hood
but not too surprised. I saw 3.7 inches of water pressure in front of
the rad at about 80 MPH speedometer but I probably had a five or 
ten MPH headwind. 3.7 inches of water is .139 psi. About the dynamic 
pressure at 88 MPH.  

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.

I also saw 1.55 inches or .058 psi up under the hood back by the 
firewall. If we assume this is the pressure all over under the
hood and the hood is roughly three feet wide by four feet long that
represents a lift on the front of the first gen  RX7 of about 
100 pounds at only 85 MPH. 12 square feet, times 144 square inches per
square foot, times .058 psi is 100 pounds! If your race RX7 weighs 
2000 pounds and 50% is on the front that is a 10% reduction in 
cornering G's!!! The rear is not going to corner any faster
than the front. 

If there are any secrets in racing stock body cars
this is at the top of the list. As Lynn Hanover would say; "you
are leaving a lot of cornering power on the table".

More about building low cost manometers later.

Paul Lamar
 
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