Do you really think that is what those slits are for? Seems like if they wanted to reduce compression they could have done it by increasing the combustion chamber size, increasing the deck height, etc. Those slits extend upwards from the transfer ports, and I just am not sure what their function might be. I was pondering that again just yesterday.

As the piston ring uncovered those slits, it would send combustion pressure and exhaust gases pulsing into the transfer port. Then when the exhaust port opens, that would stop and internal flow would be as normal. I keep wondering if it isn't a form of exhaust gas recirculation. Maybe some of the exhaust gases that enter the transfer ports never get exhausted, thereby giving "EGR".

I would like to know for sure why they are there. My brother has a Ryobi that runs quite well. When I pulled it apart to clean it after a crash, I was quite surprised to find that it had the slits. Has anyone done a controlled comparison to find out if and how much power they cost????

AV8TOR