Da-kuk/Getty ImagesInternal combustion engines are quite complex, even when you strip them back to basics. In essence, assuming you have the correct air-fuel mixture, it enters the combustion chamber, gets compressed and ignites, moving the piston, spinning the crank, and pushing the vehicle down the road. But there are so many other things going on to optimize the process. For one, there's the timing of the ignition itself, which can be advanced or moved back, to either increase power output or prevent dreaded knock, also known as detonation. But there are even finer details to discuss.Like quench — and we're not talking about relieving the engine of its thirst. No, instead we're talking about the space between the cylinder head and top of the piston when the latter is at top-dead center (TDC). So instead of pouring Gatorade into the intake manifold and hoping for happier performance, or a pleasant scent from the exhaust pipe, this fine detail has a big impact on performance and emissions.Let's discuss the vital role that combustion chamber quench — also known as piston-to-head clearance and quench height — plays, including what some ideal measurements are depending on connecting rod material.AdvertisementAdvertisementRead more: 11 Huge Engines With Surprisingly Low HorsepowerIt's all about turbulenceOctavian Lazar/Getty ImagesAs the air-fuel mixture leaves the intake manifold and reaches the combustion chamber, it slows down, and the fuel droplets leave the air stream and puddle up together. Quench mixes them back together.Ideal quench causes more turbulence and velocity in the combustion chamber, cramming the air-fuel mixture towards the spark plug and reducing the chance that any bit of it goes unburned. The higher the turbulence as the piston moves up, the better-mixed the air and fuel are. This not only ensures a clean burn, but alsoprevents knocking and helps with exhaust emissions.Quench factors in the added space of the cylinder head gasket and the piston shape, and should be as tight as possible without piston-to-valve contact. Marlan Davis points out for Hot Rod Magazine that a good rule of thumb is 0.038 to 0.043 inches of clearance with steel connecting rods, and with aluminum units, it should be increased to 0.050 to 0.065 due to them getting longer with heat.AdvertisementAdvertisementHe also points out that old-school emissions-minded V8s, like the later '70s' Chrysler 440, had over 0.06 inches of quench as a way to, what was thought of at the time, lower compression and reduce detonation. However, common modern theory says that this creates more unburned gases, and means knock has a tendency to rear its ugly head.On the flip side, quench shouldn't be tighter than 0.035 inches, and it should be increased if the piston has enough rock at TDC to stick out above the block deck. This can be achieved with a thicker head gasket. Combustion chamber quench plays a vital role in engine performance, as it determines how well-mixed the air-fuel mixture is before it's lit off by the spark plug.Want more like this? Join the Jalopnik newsletter to get the latest auto news sent straight to your inbox, and follow us or add us as a preferred search source on Google.Read the original article on Jalopnik.