Ethanol Fuel Blend Calculator

When to use it

• Compare how a change in final tank volume affects high-ethanol fuel to add before committing to parts, setup, or strategy changes.
• Check a workshop, dyno, simulator, or trackside spreadsheet result using a transparent formula: Tank × (target − current) ÷ (source − current).
• Use the result with known fuel density, measured fuel pressure, realistic duty-cycle limits, and logged lambda data. Fuel systems should be sized with headroom because demand changes with boost, temperature, fuel type, and engine safety targets.

How to use it

1. Enter final tank volume in L; the default value shown is 50 L.
2. Enter current ethanol in %; the default value shown is 10 %.
3. Enter source ethanol in %; the default value shown is 85 %.
4. Enter target ethanol in %; the default value shown is 40 %.

How to read the result

High-ethanol fuel to add is shown in L. Use the number as a calculated reference point, then compare it with measured data from the car, the part supplier, or the race environment. A mathematically clean answer can still be unsuitable if the inputs are estimated, rounded, measured under different conditions, or outside the normal range for the vehicle.

Assumptions and checks

• Assumes the remaining volume is the current blend and volumes combine ideally.
• Changing final tank volume and current ethanol together can move the answer in ways that are easy to miss, so make related setup changes deliberately.
• Confirm the fuel type and density when converting between mass flow and volume flow.
• Keep injector duty cycle and pump capacity below their practical limits with a sensible reserve.
• Verify fuelling changes on proper measuring equipment before relying on them at full load.