What is quench and is it important?
A. This article gives a very good explanation. The Jeep 4.0L engine is blessed with a cylinder head that has kidney-shaped combustion chambers and dished pistons that promote swirl and reduce the tendency for the engine to detonate. The piston/head combination also has two quench areas where the pistons come into very close contact with the head at TDC, thus pushing hot gases back into the combustion chamber and promoting more swirl. A tighter distance between the flat part of the piston crown and the head (quench height) promotes even more swirl, allowing you to run the engine on lower octane fuel without experiencing detonation.
