RC car engines have used transfer ports somewhat like that. They use Yam 12 (very poor) transfer passage shapes, though. We were able to improve the power of a 35 cc race engine with the pictured liner modification. The stock liner is on the left. The best power modification is the second liner from the left. All these designs try to block the flow out of the exhaust. I think the RC car liner designs may also be for marketing more than serious performance improvement. They come out with different porting every few years.
Lohring Miller
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