Guides
Correcting an Ethanol Blend
You overshot or undershot your target ethanol blend. Here is how to fix it — adding fuel, draining, or burning down — and how to work out the exact amounts.
How to Test Ethanol Content
How to measure the actual ethanol percentage in pump E85 or gasoline using a simple water-separation test, why it matters, and what the result does and does not tell you.
Seasonal E85 Ethanol Content
Pump E85 ethanol content changes with season and region. What the ASTM classes actually permit, what surveys have measured, and what to assume where you live.
Why E85 Is Not 85% Ethanol
The number in the name is not a specification. What ASTM D5798 actually permits, and why real pump E85 is usually well below 85% ethanol.
Why We Do Not Show Octane
Ethanol blending octane is non-linear and base-fuel dependent. Why a linear octane estimate is wrong, and why we would rather show you nothing than a wrong number.
What Is E85?
What E85 is, what it contains, which vehicles can use it, and what it does for a performance engine.
Mixing E85 With 93 Octane
How to mix pump E85 with 93 octane to reach a target ethanol blend, why the ethanol already in your 93 changes the answer, and how to mix so it actually combines.