I just filled my 993 with 91 octane without ethanol for the first time. I've always filled with 93 octane (with ethanol) because I thought the octane rating is what I should be looking for. Now I'm confused, because it seems to develop more power on the 91 octane without ethanol. Can someone enlighten me?

 

Placebic.

 

Not sure, but it makes sense to use the no ethanol version, if storing it for many months.

 

Too funny you just brought this question up. I was going to ask about the same question. Better to run a lower octane of non-ethanol or a higher octane with it?

 

I noticed this too, on the track during a DE. As I understand it, ethanol burns at higher temp hence raises octane. However does not appear to produce as much power as gasoline, ie the explosion of fuel/air in the cylinders isn't as powerful, in our engine setup at least. Might be a different matter in F1 engines tho.

In my case part of it may be that I live at about 3500ft altitude, where higher than 91 octane may not be useful ie not enough air density to take advantage of it.

 

Sounds like you have a very sensitive AND accurate butt dyno.

Gasoline holds more energy than does ethanol, so running pure gas will yield more power than running an ethanol blended fuel. We're talking here about running the two fuels through the same engine and engine management. Some race fuels run a much higher percentage of ethanol than the pump gas we get at gas stations. Because the ethanol has very high octane numbers (octane = detonation resistance rating) tuners can take advantage of this with very aggressive ignition timing. However at the same time they will need to be burning larger quantities of fuel to get the same # of calories. The side benefit is better piston cooling.

So when we burn pure gas in our cars we get more HP and more MPG.

Oh, and ethanol burns slower, and cooler than gas. This = higher octane rating.