closed chamber vs open chamber edelbrock heads

A quench design has a portion of the piston come very close to a portion of the head opposite the piston. This forces all the mixture from the side of the chamber over towards the piston a a high velocity promoting better mixing and makes the engine less susceptable to detonation. This will allow you to run a higher compression ratio.

For example: My 360 with closed chamber magnum heads was built with the pistons at zero deck. With an 0.039 head gasket the flat portion of the that extends over the piston comes with in 0.039". I have 10.6:1 compression in my engine and it will run without detonation on 89 octane gas.