Editing Quench

==Introduction==
[[File:Squishband.jpg|thumb|350px||]] 
Quench (or squish, or "squench") is sometimes referred to as "mechanical octane". It decreases the need for octane by promoting a more homogeneous air/fuel charge in the combustion chamber and it also helps promote flame travel.

==What is quench?==
Quench is the name given to the turbulent mixing of the air/fuel mixture caused by the close proximity of the piston to the quench pad(s) of the cylinder head. As the piston approaches top dead center (TDC), the clearance between the crown of the piston and the quench pad of the cylinder head diminishes to about 0.040" (steel rods, aluminum rods require more distance). This squeezes or "squishes" the air/fuel mixture from the area where the piston and head are closest, to the area where the combustion chamber is located. This action creates turbulence to achieve a more homogeneous mixing of the air/fuel mixture. A quench distance of ~0.040" will allow a high performance engine to run without detonation using less octane than would otherwise be needed. Of course this is providing that all the other important areas are also covered, like the static and dynamic compression ratios, correct air/fuel ratio, correct plug heat range, good ring and valve guide seal, etc.
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==How to arrive at the target quench figure==
One way to arrive at a ~0.040" quench distance is to cut the block decks to zero piston deck height and to use a head gasket that compresses to around 0.040". This allows a [[quench]] (or squish, or "squench") measurement of 0.040". 

==Parts stack height==
When the parts that make up the reciprocating assembly are selected, these parts have to fit into the SBC block deck height of ~9.025". When calculating the height of the parts that make up the reciprocating assembly, use 1/2 of the stroke. To that, add the rod length, head gasket thickness, piston compression height. 

The height of the parts needs to be right at 0.040" less than the deck height of the block.

In a running engine, the oil clearance will create a slightly longer stack- a 0.003" rod bearing oil clearance will add something slightly less than 0.003". In this article, oil clearance will NOT be added into the stack height. If desired the oil clearance may be added; easiest way to do this would be to either add the oil clearance to the rod length, or simpler yet, just add the oil clearance after the stack height is calculated. The added height from the oil clearance would only be an issue if the engine is being built with a marginal amount of quench (<0.035" for steel rods); if built with the "ideal" 0.040" quench, the oil clearance can be basically ignored.

Another consideration is piston "rock". At TDC as the piston transitions from upward to downward movement, the piston will tip on its wrist pin. This causes one edge of the piston to be a small amount higher than the other edge. The exact amount will vary with how much piston to wall clearance there is; more clearance means more piston rock. Forged pistons generally have a looser piston to wall clearance than cast pistons, but newer design forged pistons have tighter clearances than was used in days gone by. This is another thing that's basically accounted for if a 0.040" quench distance is maintained. Only if less than 0.035" would this possible be an issue. 

The bottom line to all this is it's best to maintain an adequate quench figure of 0.040". There's nothing to be gained by going tighter, and a 0.040" quench distance will avoid unseen problems for the most part. If the quench is less than 0.040", be sure to double check clearances to be sure there is no contact between the piston and head- for obvious reasons.  


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[[Category:undeveloped articles]]
[[Category:Engine]]