“The cowl pressure is too great because the cowl air exit is not large enough or the inlets are too large…”

 

BALDERDASH!  (Whatever that is.)

 

You are being sandbagged by a colleague with a slower airplane.  (It happens.)

 

If the engine cools OK, then there is no point in making inlets or outlets larger.   It will only increase cooling drag and overcool the engine.

 

The cowl pressure will be high at high cruise speeds, approaching the pressure measured by the pitot tube, that is, the ram pressure.  At 200 KIAS the ram pressure is about 1 psig.  At 250 KIAS, it will be roughly 1.6 psig.

 

Now consider your oil door.  Imagine it is 4 by 5 inches, 20 square inches. 

 

Conduct the following mental experiment.  Remove top cowl, invert, and place on pillows to keep the oil door off the floor.  Put 32 pounds of lead shot bags on the oil door to push it out.  Add some vibration. 

 

No wonder those two wimpy rivets failed. 

 

Reinforce door and go flying, snug in the fact that your cowl is delivering good pressure recovery. 

 

And minimize cooling drag!

 

Fred