Quench is the distance between the top of the piston at TDC and the cylinder head surface. It is also called "Squish" or "Piston-to-Head Clearance."
How is it measured?
Quench is a calculated dimension. It uses the following formula:
Quench = Deck Clearance + Compressed Head Gasket Thickness
How does it affect performance?
The right amount of quench can promote fast, complete burn of the air/fuel mixture. It creates turbulence, which forces the air/fuel mixture toward the spark plug. This reduces the possibility of Detonation. It also leads to cleaner emissions.
What should it be?
Quench should be as tight as possible, without the piston contacting the head. Recommended quench depends on your max rpm and the type of connecting rods you use.
| Max RPM | Connecting Rod Type | Quench Range |
| 6,000 or less | Steel | 0.035 - 0.045 in. |
| 6,000 + | Steel | 0.038 - 0.043 in. |
| Any | Aluminum | 0.050 - 0.065 in. |
Notes
- Aluminum rods get longer as they get hotter.
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- Increased quench will prevent the piston from contacting the head.
- Don't run more than 0.060 in. quench trying to lower Compression Ratio.
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- This will slow the combustion process and could cause Detonation.