I'm finally taxiing my HKS-Kitfox project, and am having troubles with the CHT over temping on the HKS when I have the cowl installed. It seems to be OK when I'm moving, but it will redline if I'm stopped and run it up for a short while. And once the temps get high, they won't come back down at idle.

Some baffling may help, but I've yet to find any photos of a HKS in the cowl that has any baffles attached. So, I'm looking at the air exit for now. I've read quite a few times online about a 3:1 ratio to the cowling inlet as being a good exit size, but with a large 13" round cowl opening on the front, there is no way I'd get there without removing the whole bottom cowl. Anyone else with an air-cooled engine want to tell me how large their cowl exit is?

Another thought is that the airfoil portion of the prop blade appears to start at the edge of the cowl opening, so maybe there is no airflow happening at all in the cowl when stopped. I'd like to try out a venturii lip on the bottom edge of the cowl in hopes that it would create some suction from the prop blast going across it, but I haven't been able to find any info online on how to design one. I looked at two aircraft on the field (Stinson Voyager and Piper Pacer) both of which have an exit opening lip. They both appear to be 45 deg to the cowling surface (nearly pointing straight down when the aircraft are on the ground). The Stinson's is about 1.25" tall and the Pacer is almost 2". Anyone else played around with cowl exit lips?