Very little if none at all. Optimum quench "they say" is "around" .035". I think the piston on the early 340 was around .020" or so out of the hole. The head gaskets they used from Chrysler were the .020" steel shim gaskets. The chamber depth opposite the spark plug (which is where quench would occur) is generally in the .095" deep area. So, the .020" on both the piston and head gasket cancel each out. So you're lookin at a quench distance of about .095". That's not enough for any quench......although the piston being out of the hole adds compression, which was the goal.
