E85 vs 93 octane: which is better?

For power, E85 usually wins. Its effective octane is roughly 100–105 (R+M/2) versus 93 for premium, and ethanol's cooling effect lets boosted engines run more timing and boost safely. That's why ethanol is a staple of the tuning world — it's the cheapest path to race-fuel-adjacent octane.

The trade-offs

• Fuel economy: E85 has ~27% less energy per gallon, so you'll burn noticeably more of it than 93.
• Availability: 93 is at nearly every station; E85 is not (finding E85 takes a map).
• Consistency: 93 is a known quantity; pump E85 varies 51–83% ethanol (why), so its octane shifts.
• Hardware: full E85 needs the fuel system to support the higher flow; many run a blend instead.

The popular middle ground: blend them

Lots of tuners split the difference by blending E85 with 93 to a target like E30 or E50 — more octane than straight 93, better economy and easier fueling than full E85. The right ratio depends on the real pump ethanol %; here's the math, and E85 App's calculator does it for you.

So which should you run?

For a daily driver, 93 is simpler. For a boosted/tuned build chasing cheap power, E85 (or an E30–E50 blend) is hard to beat — just budget for the MPG hit and confirm your car and tune support it.