Estimate a volume-weighted blend or solve the linear mix for a planning target. Actual finished-fuel octane can be non-linear, so critical combinations require supplier data or testing.
Blending fuel changes the mixture's knock resistance, but the result is not guaranteed to equal the volume-weighted average. Use these equations for planning only and keep both input ratings on the same scale.
Finished-fuel octane depends on component chemistry, and blending can be synergistic or otherwise non-linear. Ethanol-containing fuels and additive packages are especially poor candidates for assuming an exact weighted average. The E85 Blend Calculator solves ethanol percentage, not octane. For a calibration that depends on a minimum octane, use supplier blend data or test the finished fuel.
Octane is measured with standardized engine tests. RON and MON use different conditions; their difference is fuel sensitivity. US pumps post AKI, or (RON + MON) / 2, while many other markets post RON. There is no fixed RON-to-AKI offset because sensitivity varies. Before calculating, make sure both fuels use the same rating scale.
Octane rating measures resistance to knock under standardized tests. A higher rating can provide useful knock margin when an engine and calibration can use it, but it does not by itself guarantee power or make a boost/compression combination safe. Follow the vehicle or tune requirement; assess mixture, timing, charge temperature, fuel pressure, and knock behavior with suitable instrumentation.
Suppose you have 10 gallons of 93 AKI pump gas in the tank and want to reach 100 AKI for a track day using 110-octane unleaded race fuel. Use the target formula:
The linear model returns 7 gallons, producing a 17-gallon blend with a weighted estimate of 100.0 AKI. That verifies the arithmetic, not the actual tested octane. Confirm compatibility, unleaded/leaded status, rating scale, and finished-fuel performance with the suppliers before relying on the result.
The US EPA technical literature on gasoline blending explains that octane response depends on composition and may be non-linear. The calculator intentionally labels its output as a linear estimate.
Many high-octane race fuels (110+) are leaded - even small amounts permanently damage O2 sensors and catalytic converters. For street-driven cars with cats, stick to unleaded race fuels (e.g. 100-104 unleaded) or ethanol blending.
A volume-weighted average provides a planning estimate: (volume1 × octane1 + volume2 × octane2) ÷ total volume. Actual blend octane can be non-linear, so verify critical mixtures with supplier data or testing.
Not necessarily. Octane blending can be non-linear and depends on the chemistry of both components. Treat the volume-weighted answer as a planning model rather than a guaranteed finished-fuel rating.
RON and MON are standardized tests run under different conditions. US pump AKI is (RON + MON) / 2, while many other markets post RON. There is no exact universal conversion offset because RON minus MON varies by fuel.
Octane rating measures resistance to knock in standardized tests. Suitability in an engine also depends on load, temperature, mixture, timing, chamber design, deposits, and calibration.
Higher octane can help when the engine or calibration is knock-limited, but it does not guarantee more power. Follow the required fuel and verify changes with appropriate logging or testing.
Boost and compression are important knock variables, but neither creates a universal octane requirement. Match the fuel to the complete engine and calibration.
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