RV7A, Lycoming Thunderbolt YIO-390-EXP. 10:1 compression, Airflow Performance FM200 with ram air, dual P-Mags with Engine Bridge timing controller.
I couldn’t climb full power at less than 130kts and keep Cyl temps below 410. In cruise at 8500 I had to run lean of peak to get temps below 380, rich of peak operation pushed into 400 degree territory. Had to run retarded timing (max 25 degrees) to help temps.
Last week I installed Van’s new cowl louvers kit. Total time for the install was about six hours spread over a couple of days. Pretty easy quick job if you already have on hand the fiberglass supplies.
Did a long test flight and I’m very pleased with the results. Full power climb to 8500 @ 120kts and 1200fpm resulted in all cylinders below 400. Cruise flight rich of peak now possible with temps in the 380 range, LOP now in the 330 range.
Overall I’m seeing a 20 - 30 degree decrease in cylinder head temps. Additionally, I’m now running a max ignition advance of 29 degrees with a base timing of 21 degrees (angle valve engine timing is 20 degrees BTDC).
So the big question is how did it impact my airspeed? This is pretty hard to answer. I’m actually going a few knots faster as I can run the engine a bit harder and with a little more advance. I tried running the same LOP fuel flow as before and might have seen 2 kts higher TAS, but density altitudes and other factors were certainly different. I think it is safe to conclude that the louvers had little to no impact on airspeed.
One other factor in my plane was the presence of the heat muff that partially blocked the exit air on the right side of the cowl. Along with the nose wheel mounts, the exit air area on my plane was pretty restricted. That may also have been a factor that made this mod so successful on my plane.
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Mel Jordan
Tucson RV-7A
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