As I reported yesterday, I did a phase one climb test to 10,000' at WOT to see what the temps would do. OAT was 78F at take off, hottest CHT was 377 max oil temp was 175.
What I did not mention was that on the very first taxi test, hottest CHT was 395 just taxiing around for a half hour. That was unacceptable and immediately decided to open exit area as a 4 pipe exhaust system does take up some of the existing area.
The bottom of the cowl was opened forward of the standard area 4"x12" and in effect nearly doubled the exit area. I did not see anything like 395 again during taxi tests.
This is a contentious subject with cooling purists, but I believe the best way to improve cooling is to reduce the internal cowl pressure in the lower end of the engine compartment and the way to do it is increase exit area. It worked with the 7A with the Subby H6 and the conversion to the Lycoming IO360. You can increase exit area by cutting forward of the opening or by installing louvers.
I do not like CHT issues...