George,
I'm using a Rod Bower Filter since 120h now. The systems works very well. I used to start with an older design and upgraded to a bigger flapper valve and bigger holes for filtered air intake. The pictures are made before the upgrade. I actually use a Lycoming IO-390. The aluminum intake ring in the cowling is also available from Rod. The difference from filtered to ram air is about 1.2" in cruise and you really feel a difference when you open the valve. There is some very fine dirt sticking on the inside of the fuel meter intake from the unfiltered ramair use. But I don't think this will harm the engine... When the valve is closed the engine will get warm filtered air from inside the cowling. As soon as I'm airborn I open the ramair valve. I'm happy with the system!
Christian
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