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An Overview of Flex Fuel Calibration

February 20266 min read

An Overview of Flex Fuel Calibration

Flex fuel calibration is one of the most popular upgrades for turbocharged performance builds. It allows your engine to run on any blend of E85 and pump gasoline — automatically adjusting fueling, ignition timing, and boost pressure based on the ethanol content detected by a flex fuel sensor.

How Flex Fuel Works

A flex fuel sensor (also called an ethanol content sensor) measures the percentage of ethanol in the fuel in real-time. The ECU reads this signal and interpolates between two calibration maps:

Pump gas map (0% ethanol) — conservative timing, lower boost, richer mixture

E85 map (85% ethanol) — aggressive timing, higher boost, leaner mixture

At any blend in between, the ECU automatically calculates the correct fueling and timing. This means you can fill up with whatever's available — E85 when it's cheap and accessible, pump gas when it's not — and the car adapts automatically.

Why E85 Is So Good for Turbocharged Engines

Ethanol has several properties that make it ideal for turbocharged applications:

Higher octane rating — E85 has an effective octane rating of ~105 RON, allowing more aggressive ignition timing

Cooling effect — ethanol absorbs heat as it evaporates, reducing intake charge temperatures

Stoichiometric AFR — E85's stoich is ~9.8:1 vs 14.7:1 for gasoline, requiring more fuel but providing more cooling

The result is typically 10-20% more power on E85 compared to pump gas, with better reliability due to the cooling effect.

What's Required for Flex Fuel

To run flex fuel, you need:

Flex fuel sensor — measures ethanol content (Syvecs part SYV-FLEX)

Compatible ECU — Syvecs, MoTeC, Life Racing, and EcuTek all support flex fuel

Fuel system capable of E85 — injectors, fuel pump, and lines must be E85-compatible

Proper calibration — a skilled calibrator to develop both maps and the interpolation strategy

We calibrate flex fuel builds regularly across Syvecs, MoTeC, and EcuTek platforms. Contact us to discuss your build.

Jason Bentley

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