I have one of the 2004 Subies with the stock turbo. I've been using 93 octane gas as recommended, which is normally no big deal, since I usually only fill up every few weeks. But soon I'm going to be taking a cross- country drive, and the extra cost of the premium gas is going to add up over thousands of miles.
I'm not really a car expert so hopefully someone who knows about these things can fill me in. The car has a knock sensor right? And a knock sensor lets you use regular gas by changing some timings or something right? I've heard it takes some of the power out of the turbo. Other than that, is there a big downside?
Basically, the big question on my mind is if I can somehow save some $$$ by using regular gas for my trip. I can't really imagine needing the turbo boost when I'll be mostly on cruise control at 75. Is this practical?
You may find that your warranty will be voided if you don't use the recommended fuel.
When I got my 2000 Forester GT turbo here in Oz, I asked Subaru the same question and was told that if any damage was caused through incorrect fuel usage, all warranty would be voided (apparently they CAN tell!). I am no expert either, but according to Subaru mechanics, damage WILL occur if standard fuel is used on the turbo engine for extended periods.
Once you put < 93 octane in the tank, you will pretty much never have 93 in there again, as it will always be diluted. Also, IIRC, the reccommended octane is 91- it's just not available everywhere.
It will knock like a bugger and you can do real damage to the car. Detonation is a big issue in turbocharged engines. The boost pressure comes up with RPM. At 75 MPH, I would bet you have significant boost pressure.
I am curious though. If you can't afford the extra couple of dollars for the correct fuel, why would you by a turbocharged car?
A reasonable compromise is to alternate fill-ups between premium and a lower grade when the tank is about 1/3 full. The resulting mixture should minimize any power decrease by the engine management system. I had a turbo
Nobody has asked you the requisite questions, to which your answers to your questions can only be guessed at.
1) Where are you located? I couldn't figure that out since your email address is not valid, and you used a web service to post.
2) Which car do you own?
The basic problem of not knowing where you're at is that the numbering systems for antiknock resistance is different in various countries. The system used in the US/Canada is called the Anti-Knock Index (AKI) or (R+M)/2, which is the average of the Research Octane Number (RON) and the Motor Octane Number (MON). "Regular" fuel sold in the US is
87 (R+M)/2, while typical "premium" fuel is at least 91 (R+M)/2.
In other countries, only the Research Octane Number (RON) is used. Most pump fuel has a higher RON than (R+M)/2 number. A Toyota manual I have says that in addition to the (R+M)/2 numbers, they consider "regular" to be 91 RON, while "premium" is 96 RON. Every once in a while, there's some crazy Usenet argument when people don't understand the difference and talk about how crappy the fuel sold in the US is.
As far as I know, the US Spec Subarus either recommend 87 octane,
91 (Turbos) and 93 (STi) - in (R+M)2 rating. 93 (R+M)/2 is extremely difficult to find in the US. I've never seen it before in California.
A knock sensor is supposed to detect the **onset** of knock, before any damage occurs, and retards the timing (ignites each spark earlier). Toyota sells their V6s as fine with regular, but better with premium. Others sell them as "please use premium", but "it won't kill the engine" if you use regular.
Turbocharging an engine increases the combustion chamber pressures, and makes it more likely to explode spontaneously before the spark ignites the fuel/air. A "higher octane" just means that they fuel resists this spontaneous ignition before the spark.
When you say cruise control at 75, it sounds like you mean 75 MPH (i.e. United States), so I'm thinking you're in the US. When cruising, premium fuel isn't going to do squat. If you're accelerating or climbing, your car's performance is probably going to suffer.
However - if the knock sensor malfunctions, you might damage the engine.
93 and/or 94 is extremely difficult to find in the northwestern U.S. Not even the Chevrons (which *all* have 94, even up in the middle of rednecksville, NWT) down there have 93 or 94. I took my old WRX across Canada and then all the way down the Washington and then Oregon Coast, and not a single friggin' 93 or 94 octane the whole way past the border.
Those that knew what I was talking about told me to go down to the racetrack. "That's racing fuel." Arg! No it isn't!
I remember when 92 octane (R+M)/2 was typical premium sold in California. Then all of a sudden I saw these new 91 octane stickers showing up on pumps. You could tell they were new because the older 87 and 89 octane stickers were faded.
AutoWeek did a story on, "Where did the octane go in California?" Apparently this gives the refiners a little more wiggle room, and they probably have "retooled" for it. I'm guessing they're still diverting their higher-octane fuel streams for racing or aviation fuels.
Actually - the use of oxygenates such as MTBE or ethanol raises the octane rating, so that wouldn't be it.
I've heard a few things from former petroleum chemists. The whole refining process takes raw materials and distills it into any number of "streams" of different products and sub products like gasoline, diesel, lubricants, etc. It's not super precise, and they have one heck of a time trying to separate the undesirable stuff like sulfur. I think the addition of lead or oxygenates (like MTBE) is done last in the steps before storage and delivery.
Look in your owners manual under fuel recommendations. I bet it says 93 octane is recommended . No harm will come using regualr gas. You may lose some "performance" but I doubt youll know. No company will produce an engine that sensitive or they would be paying too much for warranty claims. Personal experience-
2001.5 VW Passat w/ 1.8 Turbo has never used premium in 140k miles. A lot of problems with this car but none related to fuel octane.
It is very hard to find in California, but it is readily available in most other parts of the US. It is not easily found in most places in Canada. 94 is available in Ontario, Quebec, and some parts of BC, but Supreme is 91 everywhere else.
If it is hot out and I am using 91 (I have an STi), if I don't use octane boost, the car will knock at anything above 3000 RPM irrespective of whether I am accelerating or running on cruise control. The problem is that the knock sensor can only retart ignition to a point. Unless you have a manual BOV that will allow you to reduce boost pressure, the turbocharger will build up pressure based solely on the RPM. It will knock no matter what you are doing if there is sufficient boost pressure.
Again, the ignition will not retard until it detects knock. While the damage may be minimal, it is already damging the engine when the ECU retards the ignition. Its not a big deal if this is a momentary thing. However, if it happens for a prolonged period of time, it can cause noticeable damage.
The ECU in the STi will retard the ignition by 8 degrees each step until it does not detect knock. It will then attempt to advance the ignition timing
3 degrees, check for knock, and advance it 3 degrees again, until it detects knock. Then it backs it off 8 degrees and starts over.
It is not a good thing to use anything less than the recommended fuel for the car. With the STi, the recommended is 93 or better, and 91 can be used in emergencies and nothing less should be used (right from the owner's manual). For the WRX, 91 is recommended, 89 can be used in an emegency, and
87 should be avoided.
With the STi, where boost pressures are generally higher than the WRX, the car will go into 'limp mode' if anything less than 91 is used. That opens the BOV and allows no boost pressure at all. This is a dangerous condition for the engine, and the ECU will throw a code. I was told by Subaru that if the car went into limp mode for incorrect fuel (there are a variety of other reasons it will do it) the warranty will be voided for 'unintended use or misuse'. For the extra couple of bucks per tank load, it isn't worth taking the chance.
Bullshit. Allow me to refresh your memory as to my post in this thread a mere 24 hours ago. :-)
-- Begin --
The basic problem of not knowing where you're at is that the numbering systems for antiknock resistance is different in various countries. The system used in the US/Canada is called the Anti-Knock Index (AKI) or (R+M)/2, which is the average of the Research Octane Number (RON) and the Motor Octane Number (MON). "Regular" fuel sold in the US is
87 (R+M)/2, while typical "premium" fuel is at least 91 (R+M)/2.
In other countries, only the Research Octane Number (RON) is used. Most pump fuel has a higher RON than (R+M)/2 number. A Toyota manual I have says that in addition to the (R+M)/2 numbers, they consider "regular" to be 91 RON, while "premium" is 96 RON. Every once in a while, there's some crazy Usenet argument when people don't understand the difference and talk about how crappy the fuel sold in the US is.
-- End --
That 91 RON "regular" fuel is pretty much the same as our US 87 (R+M)/2 "regular" fuel. That 96 RON "premium" fuel is pretty much the same as our 91 (R+M)/2 "premium" fuel. Right now the price I'm paying at the pump is US $2.179/gallon, which (at current exchange rate of 1.2892 AUD/USD) translates to AUS $.742/liter.
In my trips up north (via BC, it's a fun drive) I've found that every single Chevron in BC has 94. So--really, it's available everywhere there. They keep telling me the reason is the large number of harley drivers who baby their bikes.
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