Hmmmmm........Something does not sound right. I say that cheech because I have a 180 mounted in a Dynaflite Chipmunk and the engine is fully enclosed in the cowl and I have had no problem with overheating whatsoever. The opening on my cowl is only 1 1/4"X2" and the outlet at the bottom rear of the cowl is 2"X2 1/4". My engine is inverted and as luck would have it the airflow is directly around the cylinder It looks to me like you have plenty of air coming in but several people have suggested that maybe the air needs to be directed by baffles and that is a good possibility but I have to wonder if you have a big enough opening to allow the air to flow out. Doubledee says rule of thumb is 2 to 1 and I would certainly agree but I like to go 3 to 1 if at all reasonable while preserving the looks of the cowl. Also, those in the know tell me that an engine will "unload " between 500 and 1,000 rpm in the air as opposed to on the ground, so that means that at full throttle your engine is taching say 9500 rpm and in the air at the same throttle setting it may be turning 10,500. I know Saito says that the operating range is between 2000 and 11,000 rpm but that sounds like asking a lot from that type engine. If I can get my Saito's to do what I want between 8,000 and 8,500 I'm quite happy, but I'm a scale type flyer as opposed to flying aerobatics so I'm not looking for the same type of output that you probably are. If I were facing this problem I think I would double check my needle valve settings both high and low because with my limited knowledge and experience it sounds to me like you may be running just a tad lean. Hope this has been a help. Good luck .

Steve