With E85 at around 0,89€/L against €1.80 and up for 95 octane, a flex-fuel conversion is one of the best decisions you can make for your car. But a good E85 conversion is not something you improvise.
💡 In short: An E85 conversion remaps the ECU so the engine will run on ethanol. The engine becomes flex-fuel — it can run on ethanol, on petrol, or on any blend of the two.
The real savings
E85 is cheaper but you use more of it. Consumption rises by roughly 20-25% on pure ethanol. Here is what that means in practice:
| Vehicle | 95 octane use | E85 use | Saving / 100 km |
|---|---|---|---|
| City car (6L/100) | 10,80€ | 6,70€ | -4,10€ (-38%) |
| Saloon (8L/100) | 14,40€ | 8,90€ | -5,50€ (-38%) |
| SUV (10L/100) | 18,00€ | 11,20€ | -6,80€ (-38%) |
| Sports car (12L/100) | 21,60€ | 13,40€ | -8,20€ (-38%) |
Over 20,000 km a year on a saloon, the saving comes to roughly €1,100/year. The conversion pays for itself in a single tank.
Is my vehicle compatible?
The vast majority of modern turbo petrol engines — roughly 2005 onwards — can take an E85 conversion. Naturally aspirated engines can too, though the gains are more modest.
Generally compatible ✅
- Turbo petrol engines: TSI, TFSI, EcoBoost, PureTech, TCe and similar
- Naturally aspirated petrol engines built after 2000
- Most recent Peugeot, Citroën, Renault, VW, BMW and Mercedes models
Caution, or not compatible ⚠️
- Diesel engines → not compatible
- Some very old naturally aspirated engines (seals and lines that will not take ethanol)
- Vehicles with a fragile catalytic converter (needs checking)
⚠️ Important: Before any conversion, check that the injector seals and fuel lines are ethanol compatible. On recent vehicles they usually are as standard.
What the conversion changes in the ECU
Ethanol behaves very differently from petrol. An E85 map adapts:
- Injection: injector flow is increased (ethanol carries less energy per litre)
- Ignition advance: ethanol tolerates more advance, which means more power
- Mixture: lambda is adapted for ethanol combustion
- Flex management: the lambda sensor is read to adapt to whatever blend is in the tank
Flex-fuel versus a pure E85 conversion
There are two kinds of conversion:
- Flex-fuel: the vehicle adapts automatically to any petrol/ethanol blend. You can run E85, 95 octane or E10 without thinking about it. This is the option we recommend.
- Pure E85: the vehicle is tuned for E85 alone. Less flexible, but it maximises the power gain.
✅ What we recommend: The conversion Flex-Fuel at €65. You keep full flexibility while saving on every tank of E85 you put in.
The other benefits of ethanol
Beyond the savings, ethanol brings other benefits:
- More power: E85 has an octane rating around 104 — the engine tolerates more advance and makes more power
- Better cooling: ethanol absorbs more heat as it evaporates — good news for turbos
- Carbon footprint: ethanol is made from plants — a smaller carbon footprint
Switching to E85
starting today
Bespoke flex-fuel conversion · works with every tool · delivered in 30 to 90 minutes
Pays for itself in one tank.
Traps to avoid
- Do not convert an engine in poor condition — ethanol is harder on worn parts
- Avoid plug-in E85 boxes that sit on the injectors — they cannot manage the whole map properly
- Always do a full ECU conversion for a result that is both optimal and safe