bigjacksauto

I finally have the option to run ethanol free gas in our area.
Has anyone tried pure 91 octane vs 93 octane with 10 percent ethanol.
Looking for ideas of which would make more power in a stock Hhr ss?
I realize the pure gas should produce more hp. But it is two points lower on octane.
Also is there a benefit maybe a cooling effect with the 10 % ethanol?

Breadfan

Higher octane allows you to run more timing for more power. Ethanol content raises the effective octane but lowers the mileage. (simple answer here) i think above 94 on a stock tune gets no more timing advance.

bigjacksauto

I agree the ethanol is used to raise octane but at the same time you get less MPG so I am assuming less power?
So the? I still have is what would make more power on a stock Hhr ss
91 octane pure gas or 93 octane with 10 percent ethanol?

XtremeSS

Remember, your car is stock. You will always make the same power unless you tune. Its called "learn down". < this feature is sofa king stupid btw. The only thing you may notice with higher octane is better response.

843de

The main difference between 91 octane "straight gas" and 93 octane E-10 gasoline, is the slightly increased ability of the 93 octane to resist detonation in a high compression engine.

Will the 93 octane E-10 gasoline give you more power than the regular 91 octane "straight" gasoline, no. Functionally the two are the same, interchangeable and identical for all intents and purposes.

10% Ethanol in the fuel blend will lower overall fuel efficiency by approximately 2-5%, but any slight increase in potential energy brought to the table by the Ethanol is on the range of 1% more than un-blended fuel.

With either octane rating you're about at the end of the available ignition advance, so running the 93 octane fuel will allow the ECM to get out to/or close to the maximum advance algorithm.

Honestly, I think that unless you were doing back to back dyno pulls in a controlled environment, any differences will be too small to measure or quantify.

sleeper

These days seems most gas is P4 gas, aka pizz for gas

843de

Yeah, its been a long time since they wanted you to "Put a Tiger in Your Tank", and even longer since you got free maps and had to deal with a mythical creature called an Attendant.

sleeper

Very true, no more "service with a smile" & all the extras that went with it..

badassbowtie

no difference on the butt dyno for me...I found one gas station by me that has it

bigjacksauto

Thanks everyone for the input.

• xtremess I hear ya about the learn down feature I am guessing that the stock ss tune will only start pulling timing due to detonation due to low octane below say 91 octane?

• 843de thanks for the percentage explanation, It would be nice for someone to do a back to back dyno pulls with the different gases but it does sound like the learn down feature would take away any if not all gains.

• badassbowtie thanks for testing on the old butt dyno lol sometimes thats the best test of all