Indeed. I helped one of the sport class reno racers and got him to instrument the plane briefly. I ran some calcs based on the measurements and made some recommendations. He picked up about 15 kts in the first iteration! Unfortunately, I think he got impatient with the process and I had a hard time getting any more readings.Regarding cowl pressures, the important thing is to actually measure them and not assume anything about how air is going to flow. A simple gauge that measures inches of water can be had for under $50 and save many headaches if it just gets used. From my experience, radiators, oil coolers, and inter coolers will perform pretty well once the differential pressure across them gets up around 6 or 7 inches. It only takes a little leakage to allow the differential pressure to equalize and destroy the flow. Air scoops and NACA inlets cannot do their job if they are having to exit air into a high pressure area, like the inside of the cowling. The pressure in my cowling behind the radiators will have around 7" water column pressure, so to get good flow to another exchanger requires the air inlet or scoop to overcome this pressure before any flow can take place. It is easy to waste a bunch of time putting things together that looks like it will allow good air flow and cooling...
I also got to compare notes with Dave Anders for a couple of hours at the race and concluded that both in the race plane and in most of the planes I've seen, there is likely quite a bit of low hanging fruit in the cooling system, but as you say, you can't assume, you have to measure, unless you are a lot better than me. At least theoretically, I also see some apparent low hanging fruit in water cooled engines, but I've not actually had opportunity to touch one.
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