I run Wildcat YS 20/20, an OS F plug and a 16x6 prop - gives ~9,200 rpm at full throttle, static.

I did put an aluminum baffle in the intake, to direct half the airflow to the intake side of the engine. I also think it needs more open area to exhaust air out of the cowl. I'll open up the bottom of the cowl behind the intake side and see if that helps. Would like to keep it somewhat stand-off scale, but if that's not enough cooling, I'll put in the mirror image intake opening.

Thanks for the advice, Dave.