[YosarianRem]

Howdy everybody,

Newbie Here

I searched, but couldn't find out if it is OK to run 100 octane in a completely stock 2008....saw lot's of info on the Cobb Stage 1/2. Safe to do, warranty problems, etc. I'm saving for the Cobb setup but it will be awhile. Thanks for you help.

[solovus]

You'd be fine, but why would you want to do this?

[YosarianRem]

Good question....I've had Outbacks for years. I'm new to the STI My understanding (or misunderstanding) is that one could gain a noticeable performance increase from the higher octane fuel. Correct?

[Garrett]

Originally Posted by YosarianRem

Good question....I've had Outbacks for years. I'm new to the STI My understanding (or misunderstanding) is that one could gain a noticeable performance increase from the higher octane fuel. Correct?

Incorrect, you loose performance if you run your car with less-than-intended Octane.

This is engine was meant for 93 Octane to run optimally. 91 can be used because the engine's EMU can retard timing enough to stop engine knock (detonation). So, for added protection and anomalies in gas, it is prudent just to use 94 octane.

96+ Octane will do nothing for you, unless you have aftermarket mods or tunning that can make use of it.



-Garrett

[bigd]

From what I have come to understand, higher octane fuel doesn't give you more power by itself, instead its more stable. This means the engine can be tuned more aggressively (i.e. timing, boost, etc) to take advantage of it.

Lower octane fuels detonate more easily (pre-ignite, knock, ping, etc). For instance, the piston compressing the mixture causes the mixture to heat up before the spark happens. This may force the fuel to ignite prematurely and attempt to force the piston down before it gets to top-dead-center (TDC). This eventually results in engine damage since its essentially fighting itself. A more stable fuel (higher octane rating) can handle this better and instead ignite when the spark happens, which is when the ECU says it's supposed to ignite.

There's other ways to increase a fuel's octane rating instead of just running higher octane fuel such as water/meth injection. I'd stick with 91/92/93 octane pump gas since its available everywhere.

So, without tuning, you may not see any performance increase at all. I could be wrong.

[pisymbol]

100 octane will only yield you power if you go to the dyno and retune the car for it. Though I would recommend other modifications to give you more power than just 100 octane fuel.

[EtoS]

The only time I could see justifying 100 octane is if you are gonna track it. 93 octane goes a long way believe it or not. Just dumping in 100oct gas won't give you an increase, actually with most cars it hurts performance. The best octane for your car is what it's tuned to use. Be warned, unless it's a dedicated track car I wouldn't get it tuned purely for 100oct, that gets expensive fast and at least around here 100oct is hard to come by- you'd probably end up stuck on the side of the road of you're low on gas and far from home or any place that sells 100oct

[VROOM293]

07 STi tuned for 93 octane.
Example fill up when on empty;12 or 11 gal of 91 as no 93 here in cali.
Mixed with approx. 3 gal. of 100 octane. to adhere to 93 tune.

Am i doing something wrong? I notice a big difference if i dont do this mix. Albeit placebo affect is very real.

[VROOM293]

Originally Posted by Garrett

Incorrect, you loose performance if you run your car with less-than-intended Octane.

This is engine was meant for 93 Octane to run optimally. 91 can be used because the engine's EMU can retard timing enough to stop engine knock (detonation). So, for added protection and anomalies in gas, it is prudent just to use 94 octane.

96+ Octane will do nothing for you, unless you have aftermarket mods or tunning that can make use of it.



-Garrett

huh

[EtoS]

Originally Posted by VROOM293

07 STi tuned for 93 octane.
Example fill up when on empty;12 or 11 gal of 91 as no 93 here in cali.
Mixed with approx. 3 gal. of 100 octane. to adhere to 93 tune.

Am i doing something wrong? I notice a big difference if i dont do this mix. Albeit placebo affect is very real.

Close enough if it's 12 gallons of 91 to 3 gallons of 100(92.8 octane). BTW the best way to get a good mix is to put the 100 octane first before the 91.

[Garrett]

Originally Posted by VROOM293

huh

Yes, that is everything you need to know in a nutshell of how and why..! Octane is no mystery and it doesn't need to be complicated to understand.






-Garrett

[ake109]

Originally Posted by VROOM293

huh

Exactly what Garrett said.

The engine is designed for 93.

You run it on 91, the computer retards the timing (not sure about boost, depends on how Subaru tuned it) so you lose some power.

You can put in 94+ in case you want to be prudent. e.g. bad batch of 93 gas or extra hot and stressful operating conditions.

[VROOM293]

Originally Posted by ake109

Exactly what Garrett said.

The engine is designed for 93.

You run it on 91, the computer retards the timing (not sure about boost, depends on how Subaru tuned it) so you lose some power.

You can put in 94+ in case you want to be prudent. e.g. bad batch of 93 gas or extra hot and stressful operating conditions.

Our CA. piss at the pump offers 91 then 100 @3 stations in all of L.A.
brentwood 76 ,playa del rey 76 ,barrington 76.
NO 94.I wish we were so lucky!
I cant wait to put real 93 in my tank,as my car has never had the pleasure .

[VROOM293]

Originally Posted by EtoS

Close enough if it's 12 gallons of 91 to 3 gallons of 100(92.8 octane). BTW the best way to get a good mix is to put the 100 octane first before the 91.

Thanks for the breakdown and tip.

[BBBsti LTD]

I just sent this link to a MOD to suggesting to stick it, good link to calculate octane and final price of gas tank.

How to determine octane when mixing 91 and 104 gas??