Tricked again! After a plug change I noticed that #1 was showing noticeable hotter CHTs than before--maybe 25-30 degrees hotter CHT and it was going over 425F in a climb which I don't like to see, although it WAS a pretty hot day. So I swapped in some new plugs, futzed around checking for an intake leak, test flew, pulled the EGT sensor out of the exhaust and had a look (normal) and finally borescoped the cylinder. All looked normal. Then I noticed that I had gotten sloppy and installed the upper cowl with the upper baffle folded inward so that plenum air was leaking around the baffle (pic 1). I mounted the cowl correctly and voila (or "wall-ah" as some folks say), problem solved.
I used dams on the upper cowls. It is just one way of doing it but the upper baffle must make a good seal against the plenum pressure below. I have seen some new installations where the upper baffles flopped inboard--a guarantee of cooling problems with updraft cooling. Pic 2 is how it normally looks.