Believe it or not, the summer is coming 
soon the snow will melt and the snow tires will be off. Question is, do you stay at 91 octane gas?
I was told that when it gets hotter, the car will lose some kick, and its better to put 94 octane gas, which is fine, Its only a couple of cents more, and fairly available here.
Thoughts?
For our cars, use 91 octane. The only time I would suggest using a higher octane would be in the winter, as the amount of O2 is increased due to the colder weather and resulting in more fuel being supplied to balance out the A/F ratio.
Generally though, this practice of using higher octane fuels is due to a higher than stock boost / compression ratio that requires a higher detonation (knock) threshold for the fuel. You’ll notice power being restricted if the ECU detects knock and will adjust the timing accordingly.
My $0.02
Comment by ericlfg265 — February 23, 2009 @ 11:02 pm
You either have engine knock or you dont. Use the lowest octane you can without detecting knock or follow the manual which will be conservative. There is no other reason or benefit to using a higher octane rating than specified. Possible difference in knock potential in the mountains due to altitude and Oxygen levels but minimal unless you are on the edge.
Comment by wittym — February 25, 2009 @ 2:05 am
If you were using a modded ECU software that gives 30-40 more hp, it would give you like 2-4 hp increment.
You run stock, you don,t drive on a race track, sticking to 91 should be wiser.
BTW, I plan getting a WRX265 soon, and would like to know if on a longer term, this car feels nice daily, comfortable, and reasonable l/100km thirst ?
Comment by Chuck2001 — February 25, 2009 @ 8:14 pm
Chuck
Enjoy your Wrx when you get it.
day to day the car feels great, love it, its fast, its super fun, and
very comfy. Gas wise on the HWY not bad. on the street if you have a
heavy foot (which is where the fun is) the gas is not the great, but
what a ride
Comment by Samer Forzley — February 27, 2009 @ 3:36 pm
Hey Chuck, I agree with Samer. I’ve been in the 265 since about middle of November and it’s been a great machine aside from having succumbed to the spun bearing issue myself . Very comfortable seats, good seating position, lots of ‘go’ even when you’re not in boost land. Gas .. sucks.
I average about 470 KM’s to a tank and that’s with a few extra km’s into the fuel light. Big tank to fill when you do stop by the gas station – it’s approx. 65 liter tank and so it’s not cheap.
Either way, it’s a great machine.
Comment by ericlfg265 — February 28, 2009 @ 10:35 pm
I got an email from Jeff asking if the 228 HP wrx also requires 91 Octaine
my understanding is that
The two cars have the same engine, and both are turbo, the difference in the 265 is that it has different turbo components that lets it get a few extra HP’s out of the engine, you are gonna have to use 91 for the 228 as well
Comment by Samer Forzley — March 1, 2009 @ 8:35 am
One thing to note.
94 Octane found at Sunoco stations (probably the only 94 in Canada, 93 I think is available at Pioneer) is boosted with Ethanol to generate the higher rating. So the oil company takes a lower octane rated fuel and increases this by adding Ethanol. This isn’t great for injectors.
My recommendation is to fill up with 91 octane found at Shell stations. This is the only brand of premium gas that I can find which does not have ethanol added.
Run 91 nothing less. This is a turbo charged, modestly high compression engine that will generate heat. Heat causes detonation in lower octane fuels. Just spend the extra buck or two at the pump.
My 2 cents.
-JT t- minus 3 days till I pick up the 2010 WRX 5 door.!
Comment by JT — October 2, 2009 @ 12:47 pm