Engine Compression Ratio Calculator
Calculate static compression ratio for engine building. Supports head gasket adjustments, piston dome/dish volumes, and deck clearance. Essential for turbo/NA tuning.
About
The Static Compression Ratio (CR) is a primary variable in internal combustion engine performance. It defines the ratio of the maximum cylinder volume (Bottom Dead Center) to the minimum cylinder volume (Top Dead Center). Accurate calculation is critical when selecting pistons or head gaskets, as a ratio too high for the fuel octane can lead to catastrophic detonation (knock), while a ratio too low results in poor efficiency and sluggish response.
This tool accounts for the subtle volume pockets often overlooked, such as deck clearance and crevice volume. It allows builders to toggle between metric (mm/cc) and imperial (inch) units, ensuring compatibility with both JDM/Euro and Domestic parts specifications.
Formulas
The compression ratio CR is calculated by comparing the swept volume Vs and the clearance volume Vc.
The Swept Volume (Displacement per cylinder):
The Clearance Volume is the sum of chamber, gasket, deck, and piston volumes:
Reference Data
| Engine Type | Typical CR Range | Fuel Requirement |
|---|---|---|
| Standard Street (NA) | 8.5:1 - 10.5:1 | 87 - 91 Octane |
| High Performance (NA) | 11.0:1 - 13.0:1 | 93 Octane - E85 |
| Low Boost Turbo | 8.5:1 - 9.5:1 | 91 - 93 Octane |
| High Boost Turbo/Race | 8.0:1 - 9.0:1 | Race Gas / E85 / Methanol |
| Diesel Direct Injection | 16.0:1 - 20.0:1 | Diesel |
| Mazda SkyActiv-G | 14.0:1 | 91+ Octane (Special timing) |