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94cobra69ss396 · 10-07-2009, 12:57 PM

Here's some info on quench from United Engine and Machine's website.

"Excessive cylinder pressure will encourage engine destroying detonation, and no piston is immune to its effects. An important first step is to set the assembled quench ("squish") distance to .040". The quench distance is the compressed thickness of the head gasket plus the deck clearance (the distance your piston is down in the bore). If your piston compression height (not dome height) is above the block deck, subtract the overage from the gasket thickness to get a true assembled quench distance. The quench area is the flat part of this piston that would contact a similar flat area on the cylinder head if you have zero assembled quench height. In a running engine the .040" quench usually decreases with RPM to a close collision between the piston and cylinder head. The shock wave from the close collision drives air at high velocity across the combustion chamber. This movement tends to cool hot spots, average the chamber temperature, and speeds flame travel after TDC to increase power. On the exhaust cycle, some cooling of this piston occurs due to the closeness of the hopefully cooler cylinder head. The power increase occurs because the shock wave occurs at exactly TDC on all cylinders, every time. It tends to make all cylinders alike and receive more identical flame travel speed. Spark scatter tends to be averaged with the TDC kick received from a tight quench.

Some non-quench engines, such as '68 and later Chrysler V-8's, can be converted to quench type with pistons such as the KB278, KB280, KB372, and KB373. Most Mopar cylinder heads recess the quench area into the head, so a raised area on the piston is necessary to get the close collision. If you are building an engine with steel rods, tight bearings and pistons, modest RPM, and automatic transmission, a .035" quench is the minimum practical to run without engine damage. The closer the piston comes to the cylinder head at operating speed, the more turbulence is generated. Unfortunately, the operating quench height varies in an engine as RPM and temperatures change. If aluminum rods, loose pistons (they rock and hit the head), and over 6000 RPM operation is anticipated, a static clearance of .055" could be required. A running quench height in excess of .060" will forfeit most of the benefits of the quench head design and can push the engine into severe detonation.

The suggested .040" static quench height is recommended as a good average dimension for stock rod engines up to 6500 RPM. Above 6500 RPM, rod selection becomes important. Since it is the close collision between the piston and the cylinder head that reduces the prospect of detonation, never add a shim or thick head gasket to lower compression on a quench head engine. If you have 10:1 with a proper quench and then add an extra .040" gasket to give 9.5:1 and .080" quench, you will likely create more ping at 9.5:l than you had at 10:1. One way to cheat the system is to make sure the piston of choice is light on quench side and to make sure the piston of choice is light on quench side and heavy on spark plug side. As RPM increases the piston tries to cock away from quench surface, allowing a tighter quench at most all RPM. The suitable way to lower the compression is to use a KB Dish Piston. KB Dish Pistons (reverse combustion chamber) are desinged for maximum quench area. Having part of the combustion chamber in the piston can improve the shape of the chamber and flame travel. The Step Dish is sort of an upscale version of our reqular configuration. It allows some piston weight reduction and allows the quench action to travel further across the chamber. It is especially favored when large dish cc's are required."

10-07-2009, 12:57 PM	#3
94cobra69ss396 Fast & Filthy Join Date: Jun 2008 Posts: 3,840 Tweet	Here's some info on quench from United Engine and Machine's website. "Excessive cylinder pressure will encourage engine destroying detonation, and no piston is immune to its effects. An important first step is to set the assembled quench ("squish") distance to .040". The quench distance is the compressed thickness of the head gasket plus the deck clearance (the distance your piston is down in the bore). If your piston compression height (not dome height) is above the block deck, subtract the overage from the gasket thickness to get a true assembled quench distance. The quench area is the flat part of this piston that would contact a similar flat area on the cylinder head if you have zero assembled quench height. In a running engine the .040" quench usually decreases with RPM to a close collision between the piston and cylinder head. The shock wave from the close collision drives air at high velocity across the combustion chamber. This movement tends to cool hot spots, average the chamber temperature, and speeds flame travel after TDC to increase power. On the exhaust cycle, some cooling of this piston occurs due to the closeness of the hopefully cooler cylinder head. The power increase occurs because the shock wave occurs at exactly TDC on all cylinders, every time. It tends to make all cylinders alike and receive more identical flame travel speed. Spark scatter tends to be averaged with the TDC kick received from a tight quench. Some non-quench engines, such as '68 and later Chrysler V-8's, can be converted to quench type with pistons such as the KB278, KB280, KB372, and KB373. Most Mopar cylinder heads recess the quench area into the head, so a raised area on the piston is necessary to get the close collision. If you are building an engine with steel rods, tight bearings and pistons, modest RPM, and automatic transmission, a .035" quench is the minimum practical to run without engine damage. The closer the piston comes to the cylinder head at operating speed, the more turbulence is generated. Unfortunately, the operating quench height varies in an engine as RPM and temperatures change. If aluminum rods, loose pistons (they rock and hit the head), and over 6000 RPM operation is anticipated, a static clearance of .055" could be required. A running quench height in excess of .060" will forfeit most of the benefits of the quench head design and can push the engine into severe detonation. The suggested .040" static quench height is recommended as a good average dimension for stock rod engines up to 6500 RPM. Above 6500 RPM, rod selection becomes important. Since it is the close collision between the piston and the cylinder head that reduces the prospect of detonation, never add a shim or thick head gasket to lower compression on a quench head engine. If you have 10:1 with a proper quench and then add an extra .040" gasket to give 9.5:1 and .080" quench, you will likely create more ping at 9.5:l than you had at 10:1. One way to cheat the system is to make sure the piston of choice is light on quench side and to make sure the piston of choice is light on quench side and heavy on spark plug side. As RPM increases the piston tries to cock away from quench surface, allowing a tighter quench at most all RPM. The suitable way to lower the compression is to use a KB Dish Piston. KB Dish Pistons (reverse combustion chamber) are desinged for maximum quench area. Having part of the combustion chamber in the piston can improve the shape of the chamber and flame travel. The Step Dish is sort of an upscale version of our reqular configuration. It allows some piston weight reduction and allows the quench action to travel further across the chamber. It is especially favored when large dish cc's are required."