Ethanol (E85) remapping on a sports car:what to know before you start
- Combustion & calibration
- Compatibility
- Risks & legal
E85 contains roughly 60 to 85% ethanol depending on the season. Its high octane and cooling effect suit turbo engines, but its lower energy content requires much more fuel. A homologated flex-fuel kit is about legal conversion, not performance; ethanol remapping changes the calibration and falls outside homologation. Compatibility is checked case by case, and ethanol is calibrated bespoke, on the dyno, with data logging.
E85 appeals to enthusiasts for its octane and charge cooling, but it is also where a poor file can cost an engine. This guide covers combustion, compatibility, risks and how ethanol fits into bespoke engine remapping.
What exactly is E85?
▸ Composition and seasonal variation
The ethanol content varies with the season, so any calibration assuming a fixed rate is wrong part of the year.
▸ Lower energy content
Around 30% more fuel is needed for the same amount of air, which tests injectors and pumps.
▸ Octane and charge cooling
Both push back knock, giving turbo engines room on timing and boost, within mechanical limits.
Flex-fuel kit or ethanol remap: two very different approaches
One aims at legal conversion, the other uses ethanol as a calibration lever, like a Stage 1 or 2.
▸ The homologated flex-fuel kit
It lengthens injection time for legal E85 use, with no performance goal.
▸ Ethanol calibration by mapping
An application of custom engine mapping: injection, timing, boost, cold start, ethanol sensor.
Comparison
| Criterion | Flex-fuel kit | Ethanol remap |
|---|---|---|
| Goal | Run on E85 | Use ethanol in calibration |
| Legal | Homologated | Outside homologation |
| Monitoring | Limited | High |
Is my sports car compatible with ethanol?
Injection, injectors and HP pump
A diagnostic shows whether the fuel system has the margin needed.
Fuel system materials
Seals, hoses and pumps must tolerate continuous E85 use.
Classics and youngtimers
Original materials were not designed for ethanol: caution is advised.
Risks of a poorly done ethanol remap
Ethanol tolerates a lot, except approximation.
▸ Lean mixture, knock, failure
Seasonal ethanol variation can lean out the mixture and cause knock.
▸ Cold starts and oil dilution
See our article on engine oil for sports cars.
▸ Track use
Continuous fuel flow and heat require a safety margin.
▸ Driveline stress
See our article on the uprated clutch.
Why ethanol is calibrated bespoke, never with a generic file
Logs, wideband lambda, ethanol corrections
Data drives injection and timing corrections for the real ethanol content.
The Bernis Factory approach
Bespoke mapping with an engine engineer, in Signes, 700 m from Circuit Paul Ricard; feasibility confirmed case by case.
Legal framework, insurance, roadworthiness test
A homologated kit is legal; an ethanol remap is outside homologation and must be declared to your insurer. See is remapping legal in France?.
FAQ: ethanol remapping and E85
Can you run E85 without any modification?
Not recommended: the mixture runs too lean.
Can you go back to 98 RON after an ethanol remap?
Yes with an ethanol sensor strategy, or by restoring the saved original file.
Does E85 damage the engine?
Not on a compatible, properly calibrated engine.
What power gain can you expect?
It depends on the engine and hardware; it is measured on the dyno.
Is an ethanol remap suitable for track use?
Yes, if calibrated for track with margins and monitoring.
Assess your project before switching to E85
Ethanol calibration is part of bespoke engine remapping. Start with a diagnosis at our Signes workshop.
A project,
a call.
Tell us about your car and how you use it. We'll figure out the right service together, maintenance, engine tuning, chassis, restoration.
83870 Signes
Across from the Paul Ricard circuit
Monday, Friday · 9:30-18:00
By appointment only