ORIGINAL: pe reivers
open ported pistons are there for a reason. The reason is that many model pilots neglect engine cooling, in which case the open ported piston saves their day at the field. So it reduces engine life a little bit? How many of us run their engines in excess of 200 hours without overhaul?
While I certainly agree with you regarding piston porting, I feel open cylinder porting is more a matter of easier production. For example, the classic DA50 / 100 cylinder has a closed bottom port opposite the exhaust port and as a result, there is minimal piston skirt wear because the skirt is supported through most of the stroke and especially at the top and bottom of the stroke. DA pistons don't seem to show a lot of wear on either piston skirt. Early DLE cylinders had a closed intake port on the port opposite the exhaust but later versions went to open porting on all intake ports. There has been reports of excessive piston wear as a result. The Jedi in another forum even posted some photos to support this. It was also indicated that when these cylinders are used on a twin, due to different thrust angles, one piston tends to wear where the other one does not.
This is not a criticism of these engines at all, just an observation. As you say Pe, most of these engines will never run to their limits before overhaul or repair anyway. I thought it interesting that the condition was so easily viewed in the posted photos though.