FAQ: What do the Groves do?

"Without grooves, the combustion is incomplete and unburned fuel remains in the cylinder. This unburned fuel is still expanding during the exhaust stroke; with the engine idling at the end of the exhaust stroke the expanding unburned gases flow past the intake valve into the intake manifold causing poor idle.

With the grooved cylinder heads combustion is more complete leaving little unburned fuel behind, more of the fuel is used to generate power and less is used to generate heat. (That’s also why the engines run cooler). With the modified heads little or no unburned fuel remains during the exhaust stroke. With less unburned fuel to expand during the overlap period the gasses flowing past the intake valve are reduced resulting in improved idle quality."