Originally Posted by semtex

Hey guys,

As some of you already know, about a year ago I moved from Georgia up to Alberta, Canada. Back in GA I always used Shell V-Power 93 octane - it was a bit of a no-brainer. But up here, Shell V-Power only goes up to 91 octane. There's a Canadian chain called Husky, however, and they sell 94 octane. Thing is, Husky's gas is 10% ethanol, while up here Shell contains no ethanol. So I'm in a bit of a quandry and would like your opinions on which fuel I should go with.

Some additional background. I'm currently driving a 2011 STi. (I had to leave my Z in GA). Yes, yes, I know this is a Z forum, but this is the forum I call home, and I'd be in the same quandry if I had taken my Z up here with me, even more so if I ever slapped a turbo on it. In case you're not familiar with the STi, it's a turbo'd engine. I have Cobb AP running on it, and the Cobb AP comes with separate maps for both 91 and 93 octane, the latter having more aggressive timing. For the last couple of months, I've been filling up with Shell 91 exclusively. But I just couldn't resist the urge to switch to the Cobb 93 map, so a week ago I switched over to the E10 94 octane, reflashed my ECU with the 93 map, and wow, what a noticeable difference! The turbo spools up quicker and there's noticeably more responsiveness and torque across the entire band.

This is where my head gets a little muddled. From what I've been able to read on the net via Google searching, I'm going to get less mileage from the E10 due to the lower energy content of ethanol. I read another explanation that the real reason you get lower mileage is because ethanol has a higher oxygen content, so the ECU compensates by running rich (i.e., more fuel) to even out the AFR. Either way, other STi owners report a fuel economy degradation of 2-3%, and I can live with that, NP. I've also read that ethanol is actually beneficial to turbo applications because it has a cooling effect, and that, combined with the higher AKI that allows for more advanced ignition timing, contributes to the power gain. (One guy reported that he tested Husky E10 94 against Shell V-Power 91 on a dyno and got 20whp more out of the Husky 94.) So far, so good.

My big concern is durability. I keep reading conflicting things on this. On one hand, people say ethanol will harm the hoses, seals, and fuel injectors if used long-term. A lot of people also say that ethanol tends to leave deposits behind. Then there are those who counter that all modern gasoline engines in cars are designed to run fine with ethanol. I've further read that ethanol only becomes a problem if you let the fuel sit in your tank for an extended period of time, because the ethanol will separate from the gasoline and that's when it causes corrosion, leaves deposits, etc., so if you're using it in a daily driver it'll be fine. But then the naysayers say, why take the chance? Shell V-Power is proven when it comes to engine protection.

So I'm having trouble deciding between the two. My car runs better on the E10 94. The fuel economy loss is noticeable but I think I'm willing to live with it as a fair trade-off for the extra power. Internal engine corrosion and deposits, however? Yeah I'm not so keen on that. My current plan is to continue running the E10 94 and dump a bottle of Techron or Gumout in the tank every 3000 miles or so as a precaution.

Opinions? What would you guys do if you if you had to choose between Husky 94 octane E10 and 91 octane no-ethanol from Shell? (Husky is pretty reputable in Canada, btw.)