Diamond did some pistons for me w/ a small "dish" which "mirrors" the chamber of my Eddy 84cc heads. My thought is as the piston nears TDC the mix will "roll" into the chamber near the plug. These fit at 0 deck which gives me 10.2:1 comp ratio and .039 quench. So far runs perfect and easily swallows pump swill w/38 total timing. 470" low deck street toy. Hope that helps?