Knock Threshold Calculator

Estimate the detonation threshold based on compression ratio, intake air temperature, fuel octane, and boost pressure.

Input Parameters

Results

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Effective CR
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Knock Index
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Max Safe Advance
° BTDC
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Safety Rating
Note: Detonation (knock) causes catastrophic engine damage. Higher octane fuel, lower IAT, and lower effective compression ratio all reduce knock tendency. SAE J2699 knock testing standard.

Reference

Effective CR = Static CR × (14.7 + Boost) / 14.7 Knock Index = Eff_CR × 1.5 + Temp_factor × 10 − Octane × 0.3 Temp Factor = (IAT − 60) / 100 Max Advance = 40 − (KI − 10) × 2°