So my confusion is that gasoline is 93 octane, 10% ethanol drops that to 87 octane, but 15% ethanol is 88 octane. Still trying to figure out that math.
Can anybody help?
https://www.chargerforums.com/threads/octane-and-btu-explained.240618/
“All octane rating does is measure the ability of a fuel to resist pre-ignition (read that as detonation) in a higher compression engine... Higher octane fuels allow the use of higher compression ratios, and THAT does produce more power.”
https://www.smokstak.com/forum/threads/octane-and-btus.48144/
“BTU’s and Octane is like comparing apples and oranges. The purpose of octane is to raise the temapature at which the fuel ignites. It DOES NOT as most people think add power to the fuel. That is why it is called “Anti-knock” and not “Added power”. Higher octane was developed for high compression engines to keep from detonation. High compression makes more power, not high octane. This is also why you don’t see horsepower ratings for a given engine using the differant octanes of fuel. There are several good web sites that go into this. BTU’s are the amount of heat in a given about of fuel. If I remember right it is the amount of fuel it takes to raise one pound of water one degree, or something like that. Diesel has the highest BTU’s then gasoline is next in line.”
Ethanol is an octane booster.
10% ethanol is added to 85 octane gasoline to make it 87 octane.
And 10% ethanol is added to 91 octane gasoline to make it 93 octane.
That’s why most “ethanol free” gas is 91 octane.
Adding 15% ethanol to 85 octane gas makes it 88 octane.
The 85 and 91 octane gas is known in the industry as “BOB” gas, “before oxygenate blending”.