Do angle valve cylinders have the same condition as parallel valve cylinders with lack of finning on one (intake) side? Or maybe that's not universal. The cylinders on my parallel valve 360 Superior engine are certainly lacking in that area- but maybe that's irrelevant to this discussion.
Given that most of us draw (or in my case, will draw once it's flying) air from the upper plenum to feed the oil cooler, it seems to me that good sealing is necessary in any case- any leakage (parasitic loss) takes away air that could have gone past the fins or through the cooler.
RV-7 Flying as of June 24, 2012
1120+ hours as of August 17, 2021.