E85 Ethanol Blend Calculator
How the Ethanol Blend Calculator Worked
Our E85 ethanol calculator helped customers determine the correct fuel blend ratio for their tune. E85 from the pump isn't always 85% ethanol — it varies seasonally from 51% to 83% depending on your region and the time of year.
The formula: To calculate the final ethanol content when mixing E85 with regular gasoline (E10):
Final E% = (E85_gallons × E85_content + Gas_gallons × 0.10) / Total_gallons × 100
Example
Mixing 5 gallons of E85 (actual 70% ethanol) with 10 gallons of 91 octane (10% ethanol):
(5 × 0.70 + 10 × 0.10) / 15 = 30% ethanol (E30)
Why Ethanol Content Matters for Tuning
E85 has a significantly higher octane rating than pump gas (roughly 105 octane equivalent), allowing more aggressive timing and boost levels. However, ethanol requires approximately 30% more fuel volume than gasoline, so injector size and fuel pump capacity become critical factors.
Our Stage 3 E85 tunes were calibrated for E60-E70 blends. Running a lower ethanol percentage than the tune expected could cause lean conditions, while running higher was wasteful but generally safe. We always recommended customers use a digital ethanol content analyzer (we sold those too) to verify their fuel before each fill-up.
Common Ethanol Blends for Performance
| Blend | Approx. Octane | Use Case |
|---|---|---|
| E10 (pump 91) | 91 | Stage 1 tunes |
| E30 | ~95 | Stage 2 aggressive |
| E50-E60 | ~100 | Stage 3 mild |
| E70-E85 | ~105 | Stage 3 full / race |