Ethanol vs gasoline

Ethanol resists knock better than gasoline, which is why high-compression and racing engines like it. It also cools the intake charge as it vaporises, which adds power in engines tuned for it.

It carries less energy per litre, so consumption rises. On flex-fuel vehicles running high blends, a fuel-economy drop is normal and expected.

Ethanol is also a solvent and absorbs water. Older fuel systems with incompatible rubber, cork or certain metals need attention before running high blends.