OK, Paul O Wise One,
You were correct. I put small pieces of foam at the ends
of my pressure sensing tubes and now things make sense.
I thought with a small tube with about 1/16" ID the velocity
effect wouldn't be there, but I was wrong. These are very
small pressures we are measuring.
It was a 20C morning, full power climb 5200 RPM 90 knots all
the way to 3500', oil temp reached 230. Level off and cruise
at a lower RPM than normal to get things cooled off, 4900 RPM,
120 knots, oil temp eventually dropped to 210.
I seem to have about constant pressure drop accross the oil
cooler of 3-4 inches of H2O, in the correct direction.
Climbing at 90 knots, there is 1" of positive pressure on the
inlet side and 2" of suction from the big fan at the exit side.
Cruising at 120 knots, there is 3-4" of positive pressure on the
inlet side and no suction from the exit.
Shouldn't I be getting more pressure on the inlet side than this?
Perry
Well let's see 120 kts is 138 mph if my arithmetic is correct.
dynamic pressure at 138 mph is 50 psf or .34 psi or one inch of H20 is
.038 psi so you should see 9 inches of water dynamic pressure.
A good P51 type scoop properly sealed should see up to 50% to 80% of that or
about 4.5 to 7 inches. Your scoop is not all that bad. We still
need to measure the pressure distribution over the full
face of the oil cooler. One end might be seeing most of the pressure.
The water manometer is on the way today UPS second day air. It has
ten sections so use four taps equally spaced along the length of
the oil cooler core both sides.
Your problem might be elsewhere. Are you sure your oil temp gage is correct?
Where are you measuring the oil temp?. What did Mazdatrix do with
the oil thermostat button in the front of the e-shaft? What size
rotor oil squirter jets were used? You might want to mod the front
housing so the oil is coming straight out of the pump.
Paul Lamar
What about larger inlet? It's about 5 x 5 but the "ID" might be more
like 4.5 x 4.5. So that is only 20.25 sq. inches. Oil cooler is about
5 x 25 (?) for 125 sq. inches. 20/125 = 16%. I think I will try to
open it up to say 30%. That would be a 6.12" square. I need a cowl flap
on the inlet, make it really big for climb and close it down for cruise.
I haven't calibrated the oil temp gauge, but it is a high quality unit.
It measures the oil going into the engine at the oil filter pad on the engine
where I have a bypass block. Oil filter is mounted remotely near the oil cooler.
I already had one of those Mazdatrix/Racing Beat plugs in the e-shaft,
so I assume they left it in there. I assume squirter jets are still stock.
I would like to do that mod, but I'm unhappy about the size of the port
you drill in the engine. I think you are limited to 1/4" NPT or slightly
larger. My oil lines are all AN10, 1/2" NPT would be better, but there is
not enough meat there. Adapting one size to another is kludgey. I think Ian
had good success with this mod?
Perry
I would hold off until we have some more data. Any increase in scoop size
will cause an increase in drag. Polishing the inside will not hurt however.
Paul Lamar
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