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  #1  
Old 01-09-2008, 09:21 PM
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gasoline

so i was wondering, why do our cars need premium? if i use a lower grade will it effect anything? can i potentially damage something? does the gas mileage change? (i cant experiment, my speedo doesnt work, so neither does any other mileage counter). what exactly is the difference?
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  #2  
Old 01-09-2008, 09:27 PM
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i think 91 octane is the minimum but i run 89 all the time and it runs great. sometimes if you run 87 or so you will get knock from the motor unless you have the ecu chip switched for 87 to prevent knock and you car will run like utter crap!!!unless you have the chip
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  #3  
Old 01-09-2008, 09:34 PM
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The EG33 runs a 10:1 compression ratio, which is fairly high. This makes it prone to knock, or detonation, the explosive burning of fuel in the cylinders. Knock turns engines into molten hunks of metal. In fuel, octane is the component which governs knock resitance. So more octane = more resistant to knock.

Plus, with more octane you can run more timing advance (firing the spark plugs earlier for more power). The 87 octane switch in the ECUTune chip backs the timing down to a level that will not hurt the engine even on lower octane.

Many people have used regular in their SVXii without causing harm, but if you're going to put your car in a situation where it will be pushed, or the engine will run very hot, high octane is essential.
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  #4  
Old 01-09-2008, 10:05 PM
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put in teh cheap ass 85 octane; he won't know the difference.
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  #5  
Old 01-09-2008, 10:19 PM
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Quote:
Originally Posted by shelfy View Post
put in teh cheap ass 85 octane; he won't know the difference.
My car's a girl.
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  #6  
Old 01-09-2008, 10:32 PM
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Quote:
Originally Posted by Crazy_pilot View Post
My car's a girl.
ewwwwwwww.
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1997 Subaru SVX LSi "Svetlana" #185 of 640 - 09/1996 - Polo Green Pearl - 34k miles

1992 Subaru SVX LS-L "Everett" #8738 - 01/1992 - Ebony Pearl - 139k miles - 5MT shifty - Sold 07/31/2011

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  #7  
Old 01-09-2008, 11:00 PM
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Quote:
Originally Posted by Crazy_pilot View Post
The EG33 runs a 10:1 compression ratio, which is fairly high. This makes it prone to knock, or detonation, the explosive burning of fuel in the cylinders. Knock turns engines into molten hunks of metal. In fuel, octane is the component which governs knock resitance. So more octane = more resistant to knock.

Plus, with more octane you can run more timing advance (firing the spark plugs earlier for more power). The 87 octane switch in the ECUTune chip backs the timing down to a level that will not hurt the engine even on lower octane.

Many people have used regular in their SVXii without causing harm, but if you're going to put your car in a situation where it will be pushed, or the engine will run very hot, high octane is essential.

Pay attention here.

A lot of people will tell you to run regular, and while you will probably not destroy the engine running it, you will NOT be seeing the level off efficiency or performance that the SVX is capable of.

Those who say that regular won't make a difference are mistaken, but I can't really blame them. The SVX is very sensitive to knock, and has a computer that is slow to learn. If you put regular gas in the computer will throttle back timing over time to compensate, causing a lack of millage and power, but keeping the engine healthy. Most people who put regular gas in their premium required cars won't notice a difference if they one day decide to fill it up with premum, as the driving cycles one tank typically allows will not be enough to allow the computer to learn to advance timing, it is something that happens on a gradient, and over time, so it isn't noticeable.

That being said, if you got in shelfys car, drove it, then drove a car that had adapted to premium and had always run it, you COULD tell a difference, and a marked one at that. I estimate that shelfy is losing 10~20% in power and 10% in milage because of his blasphemous ways.

The rule here is thus, Subaru's engineers knew what they were doing, and I would listen to them. They would not advertise the car as premium only if it worked out just as well to run regular, as cheaper fuel is always a good selling point.


In closing, I would recommend that you look at both the "ignition timing" and "octane" entries in wikipedia and fully understand them if you want a real answer to your question. While 87 won't kill your car, it will cost more in the end due to lost efficiency.



END OF LINE.
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  #8  
Old 01-10-2008, 05:29 AM
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If you live in an area where premium is higher than 91 octane you can safely top-off with regular without worries. Running greater-than-specified octane gains you nothing.

dcb
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  #9  
Old 01-10-2008, 08:39 AM
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Burn Regular

The cars run fine on regular. As indicated by some that really know--you won't notice ANY difference in performance with regular. I have probably put as many miles on these cars as anyone here and it has all been on regular gas (86-89 octane).

The ONLY cautionary note is that if it ever does ping or run after key is turned off--THEN burn premium--or check for knock sensor problem codes.

Lee
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  #10  
Old 01-10-2008, 09:31 AM
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Quote:
Originally Posted by lhopp77 View Post
The cars run fine on regular. As indicated by some that really know--you won't notice ANY difference in performance with regular.
Says you. I was forced to visit NJ in my SVX, and ran low on gas while I was there, so I stopped for a fill. I hate not being able to pump my own gas, but I dealt with it. I was pretty low as well. After I left, on the way home, I noticed a noticeably rougher ride from the engine, what sounded like a valve tap, and not the responsiveness that I'm used to. I looked at the receipt, and sure enough, 87, even though I specifically said 92.

Under normal driving conditions, I put in 94 exclusively at the shell on my way to work.

Think about it this way: Cost difference between 87 and 92 is roughly 20 cents. On average, I put 12 gallons of gas in my car. That's $2.40 more per fill up, every 8-10 days.

If your gonna own an SVX, you can't be cheap, because premium fuel is about the least expensive maintenance item. If you want your car to last, and treat you well, I recommend sticking with the manufacturer recommendations, they're not there for show, they're there to prolong the life of your car, and enhance your driving experience.
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  #11  
Old 01-10-2008, 10:08 AM
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Quote:
Originally Posted by JaySVX View Post
.

If your gonna own an SVX, you can't be cheap, because premium fuel is about the least expensive maintenance item. If you want your car to last, and treat you well, I recommend sticking with the manufacturer recommendations, they're not there for show, they're there to prolong the life of your car, and enhance your driving experience.
these cars cost close to 30-40 K when they first came out and are a rare breed in themselves, for one i am trying to preserve mine and its gets nothing and i means nothing less that 93 octane, and will drive an extra 5 miles or walk just to get it. As everyone has said there is a reason it say premium only, and honestly the car shouldnt take less than 92 octane ever, or you risk destroying the engine.

Just FYI i have never but anything but 93 in my car and get any where for 24-26 MPG city/highway mix.
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  #12  
Old 01-10-2008, 10:30 AM
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Funny how what fuel to use is one of the most provocative topics around here.

Of course Subaru specified "premium" for a reason, and the contention that lower octane diminishes economy and performance is perfectly sensible. That said, if my own findings with my own cars supported this, I'd immediately switch to the highest octane I could find. Fact is, I routinely alternate between pumping 1/4 and 3/4 tank of premium and regular, maintain meticulous fuel economy records and conclude that, as applies to my cars and my type of driving, there is no measurable difference. Buying more octane than necessary is a waste of money, in my book.

dcb
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Old 01-10-2008, 10:44 AM
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Three things:

1. Buying more octane than you need is a waste of money
2. Yes, the ECU will "learn" what you're feeding it, but it takes a while
3. Audible knock is a bad thing

-Bill
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  #14  
Old 01-10-2008, 12:01 PM
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Later

Quote:
Originally Posted by JaySVX View Post
Says you. I was forced to visit NJ in my SVX, and ran low on gas while I was there, so I stopped for a fill. I hate not being able to pump my own gas, but I dealt with it. I was pretty low as well. After I left, on the way home, I noticed a noticeably rougher ride from the engine, what sounded like a valve tap, and not the responsiveness that I'm used to. I looked at the receipt, and sure enough, 87, even though I specifically said 92.

If your gonna own an SVX, you can't be cheap, because premium fuel is about the least expensive maintenance item. If you want your car to last, and treat you well, I recommend sticking with the manufacturer recommendations, they're not there for show, they're there to prolong the life of your car, and enhance your driving experience.
When you have owned as many as I have and driven as many miles in them with REGULAR fuel---come back and talk to me.

Lee
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Old 01-10-2008, 12:06 PM
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Quote:
Originally Posted by dcarrb View Post
Funny how what fuel to use is one of the most provocative topics around here.

Of course Subaru specified "premium" for a reason, and the contention that lower octane diminishes economy and performance is perfectly sensible. That said, if my own findings with my own cars supported this, I'd immediately switch to the highest octane I could find. Fact is, I routinely alternate between pumping 1/4 and 3/4 tank of premium and regular, maintain meticulous fuel economy records and conclude that, as applies to my cars and my type of driving, there is no measurable difference. Buying more octane than necessary is a waste of money, in my book.

dcb

Fact--they also detuned the cars from its potential. Of course they ALWAYS hedge their bets. Again--the car runs great on regular fuel. My findings after several hundred thousand miles in several different SVXi come up with the same findings you indicate--no difference--just cheaper.

Lee
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Last edited by lhopp77; 01-10-2008 at 03:48 PM.
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