OMG what a noob!

[Trace]

hey sup all. I just got my 94 legacy turbo sedan auto two days ago and am already felt like a proud owner. for $6000 CAD thank god I didn't get a corolla or a civic.

However, I don't know anything about this car. After I bought the car I pulled up at an gas station and when was about to refuel the car I stood and stared at the pump, there's 87, 89, 91, and 94...

Which one should I get??? does it matter??

Thanks for the help I'd be very appreciated!

[TheSubaruJunkie]

It does matter. Do some research on octane ratings and what it means.

And you want 91.

-Brian

[Trace]

there's going to be a lot more reading than just octane ratings... thinking of getting my hands dirty tunning this car, but i guess i'll start from the fundamentals. anyways, thanks!

[TheSubaruJunkie]

Pretty much boils down to: The higher the octane rating, the more pressure is needed to ignite the fuel mixture. The lower the octane rating, the easier the fuel is to ignite.

With our cars being turbocharged, they run at a higher compression than most cars, and if you run a low octane fuel the high compression mixed with the hotter intake air will more likely pre-ignite the fuel... before the spark plug has a chance to do its job. This results in pinging and poor performance, and in the long run could result in engine damage. The higher octane fuel will hold up to the increased heat and pressure and will not pre-ignite as easy.

If I could, i would run 94 octane in my car just cause im picky about that kinda thing. But the highest I can get here is 91, which is all i ever run.

-Brian

[ericem]

I thought turbo charged motors had less compression.

[TheSubaruJunkie]

Yes, they do. But then you add 5-7-11psi from the turbo and you have much higher compression.

By default, the engine blocks do have a lower compression ratio. But its the turbo that makes up for it.

[ericem]

Oh, thats why its not a good idea to turbo a non turbo without changing the heads and pistons I guess lol.

[TheSubaruJunkie]

Yes, thats precisely why. The lower compression in our EJ's is created by the pistons i believe. Im pretty sure the heads are identical to all other EJ22's.

[Trace]

Very valuable information guys thanks!

Learning something more practical here than I get from school everyday ><

[Imprezive]

never get anything below 91 octane. With a stock legacy turbo, you dont need 94 octane, and it wont hurt anyting but it might help a little bit. so its up to you.

[555BCTurbo]

Pretty much boils down to: The higher the octane rating, the more pressure is needed to ignite the fuel mixture.

Not really...


Octane rating measures the resistance of fuel to autoignite (preignite in our case). A higher octane fuel actually burns slower and has slightly less energy than a lower octane fuel, but because of the higher dynamic compression ratios in a turbocharged engine, the higher octane fuel allows for a more even burn and subsequently more power generation because of the compression.