B&S>>>shouldn't as long as the squish is the same. There would be a tiny bit of loss around the perimeter of the pop-up - as it obviously can't scrape the chamber.>>>
Pete>>>Two flat surfaces mating will have the smallest area>>>
OK. Thanks. Makes sense.
Another thing. Smooth arching reliefs into the heads seem like they would be better for flow drag reduction than 90 degree reliefs in the deck. Even though a bit of turbulent mixing might be lost, charge might be greater?