Jim,
My CHTs were lower with my old engine. It was a Lyc factory overhaul that only lasted 1380 hours before the bottom end was found to be worn out. My new limits rebuild runs a bit hotter cht wise, but cooler oil temp wise. It has new Lyc cyl. And my plane does have Daves cowl, but when I put it on, I didnt see any real change in CHTs from where they were. The old engine would run 340-380 on all cyl on all but the most arduous hot climbs, or extended cold letdowns.
Zach