06 STI and WRX Impreza - Premium fuel recommended or REQUIRED?

The knock sensor can detect it, and the ECU can only compensate so much. There are tons of automotive engineers around who will tell you you are wrong. Compressing air causes it to heat up. Regular burns too hot, too fast and does not resist compression; in particular with already compressed air that is hotter to begin with. That damages engines. Your EA82 may not be as aggressively timed as an STi either.

Reply to
JD
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I apologise if I am wrong, but also why I included the specifics about my car and engine, so nobody thought I was trying to do a direct comparison. Just my two cents worth from years of running different grades of gas in different cars. But also like I said, do your own comparisons. I would hope Subaru would give the computer enough timing adjust to cover the range of gasolines available to run in it's car, if only to stave off damage, but if there is not enough adjustment, I agree, you are going to damage your engine from the preignition. If timing adjust is sufficient however, do you still insist that the regular is somehow damaging the engine? If so, I would like to know what else is happening, not to be a pain, but because I am curious to learn.

~Brian

Reply to
strchild

The STi recommends 93 minimum, and 91 can be used. 89 is not recommended except in an emergency. The car is tuned to use 93. The turbo is running at about 200 KPa (roughly twice atmospheric pressure) and that causes the air charge to heat up since that is a fair bit of boost pressure. The timing on an STi runs in the 45-48 degree range when the car is cruising off boost. It will retard the timing when the boost comes on to about 15-20 degrees at wide open throttle (WOT). That's on 93 Octane! On 91 it will retard to about 5-10 degrees of advance at WOT to avoid detonation. You can't back it off too much more...

The 2.5 is slightly higher compression than the 2.0 in the WRX. Consequently, a little higher compression ratio, a fair bit of boost pressure results in some fairly dramatic cylinder head pressures. Combine that with very aggressive timing advance and it is a recipe for disaster if the fuel is too low AKI; especially if it is hot out.

You probably can get away with it in the winter when it is very cold, if you stay off the boost and don't do it often. But in the summer, you're taking your chances.

Reply to
JD

Timing adjustments has limits as to how much it can protect an engine due to using the incorrect fuel.

Reply to
Edward Hayes

Exactly. As with dynamic suspension and ABS, the best computer can't violate the laws of chemistry and physics.

Reply to
Jim Stewart

[...]

Notice the subject of this stread, however; The original poster was asking about the STi and the WRX specifically.

Reply to
k. ote

Yes, okay, very true about the limitations of the computers to do much toward altering physics, and just this morning I watched helplessly as a man insisted an attendant put regular 87 into his WRX over the instructions stating Supreme Only that were clearly labeled on the gas filler!

For my own curiosity's sake, if nothing else, since I've never heard it discussed in this group or elsewhere, at which point does damage from too low an octane rating rear it's head? Gradually over time, 10,000+ miles,

20,000+, 50,000+ miles down the road? When, if ever are the owners gonna notice the problem, if they are not otherwise experiencing bad engine knock after the first fill-up of 87? I would assume the time needed to cause damage varies as much as the circumstances each engine puts up with, and if the knock sensor has only limited ability to help, any idea what sort of lifespan increase it really adds to the motor? What about reduced fuel to the cylinders under conditions of heavy knock? Surely there are other variables the computer can play with other than just timing adjustment to prevent damage?

~Brian

Reply to
strchild

Reply to
bigjim

One major concern is that it is the higher rpm knock that you don't hear that can do irreparable damage. That can happen very quickly. The damage may show up quickly or in the case of broken piston rings it may developed oil consumption issues that get worse as the miles pile up. Man: I just don't get it when someone spends 2-40K on a nice high performance vehicle and doesn't follow the factory recommendations. When I was younger the word for them was Air Head.

Reply to
Edward Hayes

Remember, the factory isnt paying for your gas. They recommend premium just like they recommend their own brand oil and filter. Will not using subaru or ford oil make your engine die sooner? Doubtful. Will using regulaer gas cause problems? Not at all!!! Save your money and get a better stereo or something. Why give oil companies 1 cent more when they are earning record profits? Giving them money is what I call an airhead.

Edward Hayes wrote:

Reply to
bigjim

Indeed. However, if it wasn't needed and since more expensive gas is a detractor from a sale, why would they recommend it since it means fewer sales if it isn't necessary?

Bad advice Dude. A performance vehicle like an STI recommends 93 and that is what you should use. And if that's a problem for you, buy one that is tuned for regular.

Reply to
JD

Gas is close to the same price it was in '81, in 'constant dollars'. (though TAXES on gas have gone up exponetially). Except for the 3 of us where i work that have been employed in the oil industry in the past, all other co-workers whine about the cost of fuel, yet NOT ONE person carpools. many of them share the same zipcode!

Gross profits don't really say much negative about a company;

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Carl

Reply to
Carl 1 Lucky Texan

Reply to
bigjim

Yes! There is Honda Fit! And Civic! And lots of other cars with no turbo! Such as Impreza RS... a bore that she is I average 23 mpg and don't have to be light on gas.

Reply to
Body Roll

You suck, troll.

Reply to
k. ote

Buy an STi, and then come back and tell us how you put 89 in it and are "sticking it to the man."

Go on then, smarty pants.. I dare ya!

Reply to
k. ote

Reply to
bigjim

Yea you would. We both know you would.

Reply to
k. ote

Yeah you would. I have trouble on 91at times; much less regular.

Reply to
JD

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