E85 Ethanol Blend Calculator

Mix pump fuel and E85 to hit your target ethanol % — litres of each + resulting AFR.

How it works

1

Set your fuels

Enter the ethanol % of your pump petrol (E10 = 10) and your real E85 (winter blends can be ~70%).

2

Choose a target

Pick the ethanol content your map is tuned for — E30, E50, E70…

3

Get the mix

We give the exact litres of pump fuel and E85 for your tank, plus the blend's stoich AFR.

Frequently asked questions

Why measure E85 actual ethanol content?

Pump E85 varies from ~50% (winter) to ~85% (summer). Tuning for a fixed ethanol % means you should blend to a known target rather than trusting the pump label.

What ethanol % should I use?

E30 gives a safe knock-resistance gain on most stock-ish setups; bigger blends (E50–E85) need supporting fuelling (injectors/pump). Match the blend your map was calibrated for.

Does more ethanol need more fuel?

Yes — stoichiometric AFR drops as ethanol rises (14.7 at E0 to ~9.0 at E100), so injectors and pump must keep up. The tool shows the blend's stoich AFR.

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