Since there has been a lot of talk lately on this topic of quench, thought I would share what (I think) I know about it. As I understand the thinking on the squish: In an engine that has the flat part of the piston nearly hitting the flat part of the cyl head at TDC, with say .035" clearance to spare, the mixture furthest from the spark plug is shot across the chamber at high speed towards the spark plug. This swirl/turbulence action causes the entire charge to burn more completely and evenly. Especially the portion furthest from the plug. Since the flame front has started traveling across the chamber at say 36 degrees before TDC, this turbulence is shot into the flame front causing a more complete and rapid burn. Then the end charge also has the heat "Quenched" out of it as it nears the end of the chamber, hopefully preventing pre ignitiom. That is where a rogue flame front can ignite from, and travels towards the other flame front. When they collide, then that is where the Ping or knock happens. - - - Updated - - - All theory and speculation aside, the many motors I have built seem to be more responsive and produce more power with a tight quench distance.