Want to increase your engine’s power and fuel economy and reduce the risk of detonation? If you are expecting a recommendation for the latest snake-oil fuel additive, that’s a fair guess, but you would be wrong. Actually, the key to all those claims isn’t some magic potion, but rather optimizing your engine’s squish clearance.
What is squish? Squish, also known as quench, is the gap between the top of the piston and the perimeter of the combustion chamber when the piston is at top dead center. Having the right amount of squish improves combustion efficiency by forcing the fuel/air mixture that’s hiding at the far reaches of the combustion chamber towards the spark plug, which in turn leads to more power, better fuel mileage, and less risk of detonation.
In reality though, manufacturing tolerances mean that production engines may have squish figures that are a long way off from optimal. While about 0.035” (35 thousandths of an inch) is a good benchmark, stock engines may fall within the 50 to 60 thousandths range. That extra space is robbing you of power!
In this video from the MC Garage, Senior Road Test Editor Ari Henning will walk you through the steps required to check and adjust engine squish. True, checking squish is an advanced topic for the average home mechanic, but it’s actually one of the fundamentals of engine building, so even if you don’t intend to ever check squish, it’s worth knowing about.