I am curious about what octane gas to use. I have a '98 V70 AWD (180K miles) (light-pressure turbo engine) and a 2004 xc90 2.5T AWD (155K miles), along with a '98 v70 base (206K miles). For the two turbo cars, the owner's manual "recommends" 91 octane gas, but says the car can us 87.

I have been trying to figure this out for years, and I have gone through periods of time using ONLY 91 (with up to 10% ethanol), only to revert to 87 when the added cost of 91 gets prohibitive. I am not sure whether there is a noticeable change in mileage or performance.

Recently, I came across a station where they had ethanol-free 91 octane gas for about $.30 more per gallon than 87 with 10% ethanol. My mileage was significantly higher (though it was only one tank).

I guess my question is, does ethanol-free 91 octane gas offer advantages? Is it better for my turbocharged engines, especially as they age? If it's 10% more expensive but offers almost that much better mileage AND is better for the engine, it makes sense to pay, but if there is no advantage (and the increased mileage on that one tank was my imagination or a fluke), I'll stick with 87 w/10% ethanol. Any thoughts would be appreciated!