Ethanol vs octane
Thread Starter
Burning Brakes
Joined: Jul 2012
Posts: 944
Likes: 31
From: WV
Ethanol vs octane
Just found a gas station with ethanol free gasoline, but it is only 90 octane.
So that makes me wonder whether I would get better performance using 90 octane ethanol free, or by using 93 octane containing 10% ethanol?
Anyone have an insight?
So that makes me wonder whether I would get better performance using 90 octane ethanol free, or by using 93 octane containing 10% ethanol?
Anyone have an insight?
Last edited by emptnest; Dec 23, 2012 at 02:56 PM. Reason: Broaden audience
Racer
Joined: Nov 2006
Posts: 297
Likes: 26
From: San Jose California
Organic chemistry 101
The power that comes from combustible fuels comes from the energy released by breaking the bonds between molecules. Octane is a single bond hydrocarbon with eight carbons and eighteen hydrogens. The single bonds don't produce much energy but are easy to break. Therefore Octane has LESS energy than the mixture of double and triple bonded hydrocarbons that we call gasoline. Since Octane can "spread" easily, it helps prevent detonation. So never use any more Octane than you need to prevent detonation as the more Octane, the less energy in the fuel. EthanOL is a pure alcohOL (the "OL" is the clue). Ethanol is like Octane in that it allows you to run higher compression and/or more timing advance, but it contains about 20% less energy than gasoline. Ethanol, being an alcohol is corrosive and absorbs water vapor from the air. I would rather use a 90 Octane gasoline with no Ethanol than an Ethanol mixture with a higher "Octane equivalent rating".
Melting Slicks
Joined: Nov 2009
Posts: 2,922
Likes: 219
From: West Branch, MI
This has been beaten to death in the past, but I'll give you some first hand info. I live in OKC and we have 100% gas (no ethanol) everywhere. Octane is 91 for the Premium. I use it exclusively in my 98 Vette and power, performance and mileage is awesome. I took a trip to Detroit last June. Filled up with 91 100% in OKC and got 29.5mpg on that gas. Filled up in Rolla, Mo and all they had for the rest of the trip was 93 octane 10% ethanol gas. I noticed a considerable loss in power using the ethanol gas and my mileage dropped to 27mpg the rest of the trip. When I got back to OKC, I started using the 100% stuff and power and mileage is back to normal. If I were you, I'd give it a try with the 90 octane and run a couple of tanks through your car. I'll bet you see the difference. Keep us informed. 
Burning Brakes
Joined: Sep 2011
Posts: 764
Likes: 19
From: odessa FL
In theory you could make more power with the 93 octane blend over the 91 IF the tuning were optimised to take full advantage of the addl octane and the injector pulse volume set to compensate for the lesser heat content. But your mileage would inevitably go down.
We can get marine gas in this area without alcohol but its higher than ***** on a giraffe. I think its only regular grade too.
We can get marine gas in this area without alcohol but its higher than ***** on a giraffe. I think its only regular grade too.
