SiliminPro

Cylinder Pressure Estimation

Estimates the theoretical pressure inside the cylinder at peak compression, based on the dynamic compression ratio.

psi

Estimated Cylinder Pressure is

0 PSI

Diagram coming soon

Cranking Pressure: The Engine's Health Report

Cylinder pressure, often measured as "cranking pressure," is the peak pressure generated in the cylinder during the compression stroke at low (cranking) speeds. It is the direct, measurable outcome of the Dynamic Compression Ratio (DCR). This value is a vital diagnostic tool, revealing the true health and component synergy of an engine build.

From Ratio to Reality: The Physics of Pressure

The estimated cylinder pressure is calculated using the adiabatic compression formula, which describes how gas pressure increases when its volume is reduced without heat transfer.

The Core Formula

This equation links the final pressure (P2) to the initial pressure (P1), the compression ratio, and the properties of the gas being compressed.

Pfinal = Pinitial × (DCR)γ

Specific Heat Ratio (Gamma - γ)

This value represents how a gas's temperature changes during compression. For diatomic gases like air (mostly nitrogen and oxygen), this constant is approximately 1.4.

γair ≈ 1.4

Interpreting the PSI: What the Numbers Mean

The calculated pressure is a powerful indicator of your engine's character and its compatibility with your chosen fuel.

Street Performance (160-190 PSI)

This range is the sweet spot for a responsive, pump-gas-friendly engine. It provides a strong powerband and good drivability without pushing the limits of detonation on typical premium fuel (e.g., 91-93 octane).

Race / High Octane (200-250+ PSI)

Pressures in this range indicate a highly efficient, aggressive engine combination designed for maximum power. This requires high-octane race fuel, E85, or methanol to prevent destructive detonation under extreme cylinder pressures.