87, 89 or 93 octane????

I was a little surprised when my dealer told me this car is supposed to take premium only. Curious to find out what everyone is putting in. while it hurt the car to put in anything less then 93??

only as a last resort. The min you should go is 91. Its a turbo-4....no surprise it takes good gas. You WILL notice a change in the performance of the car. IMO its only a few more dollars, granted it does add up, but then again you bought the car at least partly for performance, so why be cheap now...

Always 93... if they don't have, they its 91 mixed w/ a bottle of grain alcohol to thin out the mix on the flux capacitor. Works every time!!

i use 97 octane

93 or 94, KOMENG I am jelous of you with that 97 octane stuff

The manuel recommends at least 91 octane but in a pinch, you can use 89 but it may affect performance

err... 93/94 AKI here is equivalent to the 97/98 RON stuff over in asia. So Komeng is actually has the same type of gas we have here. North America measures octane differently than RoW. I used to live in Malaysia.

ok not jelous anymore.

not cheap....ok maybe a little. guess I'll use Costco gas.

not cheap....ok maybe a little. guess I'll use Costco gas.

My Costco’s caries BP. Cant go wrong with BP for .07 less then everywhere else.

Shell 93. Dont use anything less than 91....comes with owning the car.

not cheap....ok maybe a little.

 

This is what I don't get. Generally the difference between mid-grade and premium is $.10 a gallon. That's like $1.50 a tank difference. If a buck fifty is too much for people to handle, they either bought too much car, or just don't care what the engine needs/requires. This is a turbo car which means high compression. The higher octane gas is to help reduce the chances of detonation. Putting the "cheap" stuff in, will cause your engine to essentially detune itself as to not start pinging.

 

</rant>

I use 93 from costco with no problems. It's cheaper than other station's 87

My Costco’s caries BP. Cant go wrong with BP for .07 less then everywhere else.

 

do all costco's in the chicago area (aside from chicago, schaumbug and bloomingdale are the only other locations that come to mind) carry BP? do they just brand it as costco gas, or is their actual BP signage? if not, how do you know it's bp gas? i'm not flaming, i'm just genuinely curious.

i can only get 92. i sometimes mix it with a half bottle of Torco and wind up with about a 95-96 mixture. never anything less than 92 though.

I used to use Suoco 94 all the time, then they stopped that in VA so now I just use Sunoco 93 all the time. If I cared that much about saving 1 dollar on every fill up of gas I wouldn't have bought a turbo'd car.

do all costco's in the chicago area (aside from chicago, schaumbug and bloomingdale are the only other locations that come to mind) carry BP? do they just brand it as costco gas, or is their actual BP signage? if not, how do you know it's bp gas? i'm not flaming, i'm just genuinely curious.

At the Bloomingdale one they bring it in on an unmarked truck but the driver was wearing BP clothing when filling the station (needless to say I didn’t fill up because its bad to fill the car when they are filling the tanks). I asked the attendant and he say that’s the case. For you executive members this does not count towards your 2% but I do get 2% on the Costco Amex.

 

I have also tried Mobile and BP and I always receive the same shity mileage, im not complaining I tend to shift late…really late…a lot.

Don't forget that altitude plays a part in what octane gas you can get in a particular area. Our highest here (except for a few stations that sell "special" gas) is 91 RON. At sea level the highest normal rating I've seen is 93/94 RON. Using 91 RON at sea level is just as bad as using 87 here.

 

If the car requires "Premium Fuel", that's what you should stick with regardless of the octane ratings. Don't try to get by with a mid-grade fuel just because some others are using Premium at 91 instead of 93/94.

This question consistently comes up on every discussion forum I participate in.

 

The Legacy GT and most cars for that matter MAY run no differently on 87 octane fuel. Octane has NOTHING to do with creating more power, it's simply a measurement of a how much the fuel can be compressed before it spontaneously ignites. The fuel is supposed to ignite when the spark plug emits a spark. This is supposed to be timed perfectly so the piston is pushed away from the explosion at the right time. If the fuel ignites spontaneously or prematurely due to excess cylinder temps., then this could cause piston/engine damage and that horrible engine "knock" sound.

 

Many cars today can anti-knock sensors and will reduce engine timing to prevent knock. This may result in lower fuel economy. The only way to tell is to test 87 octane and 91 octane for a substantial amount of time. In other words, use 87 octane for 10 full tanks of gas and then compare to 91 octane using 10 full tanks of gas. Compare your fuel economy. I’ll bet it won’t be any different assuming you don’t alter your driving style during the tests.

 

See this link: http://auto.howstuffworks.com/question90.htm

 

I personally use 87 octane in vehicles even when the manufacturer recommends a higher octane fuel. I do this carefully. More importantly, I do this because most manufactures' recommendations are very conservative. Their cars are sold for all kinds of different people with different uses and in different climates and altitudes. They set up their cars to be mass produced and in manner to apply to everyone to be used anywhere in the world - in other words, conservative. To quote the article, "the manufacturer's recommendation is conservative, so you may be able to carefully reduce the fuel octane. The penalty for getting it badly wrong, and not realizing that you have, could be expensive engine damage." Going from 91 octane to 87 octane is not considered a major difference. Unless you engine knocks, you are not doing any harm. You are actually saving money.

 

Some background information:

 

The likilhood of an engine to knock increases with the compression ratio. The higher the compression ratio, typically, the higher the cylinder temperature. The higher the cylinder temperature, the more likely for the fuel to ignite spantaneously and cause engine knock/damage. Higher octane fuel can simply withstand the higher cylinder temperature longer than a lower octane fuel.

 

I use 87 octane fuel in my 2003 Nissan Pathfinder. The compression ratio in my Pathfinder is actually higher than the Legacy GT (10.3:1 vs. 8.4:1). Most importantly, I have measured the same fuel economy as when I used 91 octane. If my car was losing power, then it would also lose fuel economy. I've used both fuels for an extensive amount of time and drive cycles. The ECU is adaptable and will adjust to different octane. Moving from 91 octane to 87 octane is minor on an engine with the compression ratio we are concerned with here. There is no penalty for doing so. If we were discussing engines with a higher compression ratio, then running lower octane MAY cause engine knock and MAY cause damage. If you decide to modify your Legacy's turbo and significantly raise the compression ratio, then you may want to experiment with a higher octane fuel.

 

Just remember that higher octane fuel DOES NOT PRODUCE MORE POWER! Many people purchase the 93 octane fuel because they think their car will run better or magically become quicker. It's simply not true. Octane ratings have to do with the fuel's ability to resist detonation - that's it! TV ads. have done a wonderful job of brainwashing car owners. Heck, they even name their fuels accordingly (Shell V-Power, Amaco Ultimate, Mobil Super Unleaded, etc.) If you go to any of these major fuel manufactures’ web sites, they even state that the higher octane fuel does not produce more power.

Our "low" 8.4:1 compression is not consistent like the 10.3:1 on your pathfinder or the 11:1 on my S2000. We're turboed remember that. The compression rises as boost rises. It's what a car is designed to run on. Hell the Prius' engine is 13:1, that's motorcycle levels, yet is designed to run on 87. Why put a lesser grade in and have the ECU compensate by retarding timing. Sure it may not hurt performance, but the engine isn't running at it's optimal setting.

EASY Euclid.... I'm with you on the premium gas and performance. Wouldn't risk putting anything less in for it to be cheap or to hinder performance. Being this is the first performance car I've owned, my question is more from curiousity.

Ding! Euclid got it. Using lower grade octane, depending on your area, the weather, the quality of the gas etc. will very likely cause the ECU to pull timing and you will lose power. It will do this because the car is designed to run on premium gas (California cars are designed to run on 91 because that's what premium is here), and it's a safety margin. If you run lower octane gas in your Legacy you are effectively removing that safety margin, and if the octane is too low for the conditions, the ECU will respond and pull timing to make sure you've got a safety margin again.

 

You might be able to run 87 octane and not notice any difference - as I said, it depends on the conditions in your area and the quality of the gas in question. But in most places (especially here in Cali) using low octane gas is a sure way to retard your ignition timing and lose some power.

As I was sitting here writing the "novel" below, Xactly and Euclid said what I was trying to say.

 

While I pretty much agree with everything Mono has stated, I take exception to this.

TThe compression ratio in my Pathfinder is actually higher than the Legacy GT (10.3:1 vs. 8.4:1).

8.4:1 may be the compression ratio of the engine without boost, but it doesn't reflect the "effective ratio" when the turbo is doing it's thing. Coincidentally, knock is most damaging during full boost and higher RPM's.

In comparing factory engines, nearly all normally aspirated units have a higher compression ratio than force-induction units.

 

I agree that running lower than "Premium" might be okay. I personally wouldn't recommend it to someone that doesn't really understand what engines do though. After seeing a few ruined engines in my lifetime because the owner blindly trusted someone talking out his ass, I'm very reluctant to make such a recommendation to everyone. It's really sad to see someone making payments on a new car with a damaged/ruined engine!

 

I have (as stated in another thread about this subject) logged PCM data showing that noticeable power loss can occur under the right circumstances when gasoline is not retardant enough for the situation. This was noticed on a different car so it may not be applicable to this Subaru engine.

 

I don't know if Subaru's ECM does this or not, but quite a few PCM/ECMs will pull timing for a set duration when knock is detected. In other words, when it senses knock, it might pull timing by 15-20 degrees for 1.5 seconds even if the actual knock only occurred for a tenth of a second. If knock occurs again, there's another 1.5 seconds of retardation, etc. THAT will hurt performance a great deal and is very noticeable when you have have less than 15 seconds to get to the other end of the track! If our ECMs handle knock detection the same way, it's definitely going to hurt performance more than an engine that's not giving the knock sensor a workout!

 

Lower octane probably won't hurt someone that rarely gets the turbo spooled up "properly" on a regular basis. But the lack of retardation in the fuel is going to probably hurt performance if that person ever needs to really use the turbo.

While the knock sensors are there to help protect the engine from damage, not all knock sensors work correctly and they can fail unexpectedly. That's all it would take to start tearing up a perfectly good engine!

I always use 93 in any car I'm driving. Whats a few bucks on gas your paying 190 for 89 and 2.05 for 93 the 15 cents is worth it to me.

If the compression ratio isn't high enough to warrant "Premium Fuel", you may be wasting money AND losing performance.

Whatever the manufacturer recommends includes a good safety buffer. There's no need to go above that unless modifications are made.

 

I knew a guy that claimed he used some kind of really high octane (maybe 140ish) Jet fuel in his car for a few minutes. It was a new car at the time. The engine overheated in just a couple of minutes. I doubt that he was lying about it because he took a LOT of grief for doing such a thing and never changed his story!