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

[JD]

John

Fellas, engines have knock sensors for a reason.

I had an 89 GL Turbo Wagon (EA82 / 4EAT) that I ran very hard on a long
paper route for two years (20 miles of paved, hilltop roads interspersed
with 20 miles of unpaved, washboard gravel roads, plus a 12 mile commute).
For the first year I burned Chevron regular almost exclusively, for the
second I burned Chevron supreme exclusively. There was never any damage
to the motor from the regular gas. However, the reason I switched from
regular to supreme was for mileage purposes. After averaging out my
mileage (easy to do when you run the same route 365 days a year) on both
grades of gasoline, I was spending ~$29 to fill my car with regular after
three trips around the mountain versus ~$24 to fill my car when I burned
supreme to do the same three trips around the mountain. Although no
damage was done to the car, the timing retardation due to the regular gas
killed both performance and gas mileage and in the end just cost me more
money. So, for less money, I got the performance I was supposed to out of
the motor, plus I've never had injector problems. I find this to be the
opposite of the opinion that we merely benefit the oil companies when we
burn supreme, but again, your mileage may vary on the stuff.

Having worked at the same station I fill up at, I can't tell you how silly
I find it when I see women filling their sports and luxury cars requiring
supreme with regular in an attempt to save money. I have seen benefit to
burning supreme in enough cars, I don't bother to do the math anymore for
myself. Besides, the price difference between regular and supreme never
changes, so as the cost of both rises, the potential savings with regular
diminish, while the possible benefits super has over regular stay the
same.

Unfortunately, as others have pointed out, some cars just don't benefit
significantly from the switch. So do yourself a favor and do a fair
comparison for yourself using your own math, in your own car, and then
make your assertions.

As for regular gas damaging a subaru turbo motor, I have 20,000+ miles of
hard driving on a 160,000+ mile turbo motor to say that it won't hurt an
EA82. I frequently had her to 5k RPMs and 100+MPH, however, the
performance loss is not worth the pittance I saved at the pump.

~Brian

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.

 

[strchild]

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

 

[JD]

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

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.

 

[Edward Hayes]

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

 

[Jim Stewart]

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

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

 

[k. ote]

Fellas, engines have knock sensors for a reason. [...]
As for regular gas damaging a subaru turbo motor, I have 20,000+ miles of
hard driving on a 160,000+ mile turbo motor to say that it won't hurt an
EA82. I frequently had her to 5k RPMs and 100+MPH, however, the
performance loss is not worth the pittance I saved at the pump.

~Brian

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

 

[strchild]

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

Fellas, engines have knock sensors for a reason. [...]
As for regular gas damaging a subaru turbo motor, I have 20,000+ miles of
hard driving on a 160,000+ mile turbo motor to say that it won't hurt an
EA82. I frequently had her to 5k RPMs and 100+MPH, however, the
performance loss is not worth the pittance I saved at the pump.

~Brian

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

 

[bigjim]

The ex has a 2001.5 vw passat with 1.8 turbo. She never put premium in
it and has 135k miles on it. It has had MANY problems but none due
octane issues.

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

Fellas, engines have knock sensors for a reason. [...]
As for regular gas damaging a subaru turbo motor, I have 20,000+ miles of
hard driving on a 160,000+ mile turbo motor to say that it won't hurt an
EA82. I frequently had her to 5k RPMs and 100+MPH, however, the
performance loss is not worth the pittance I saved at the pump.

~Brian

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

 

[Edward Hayes]

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.

 

[bigjim]

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.

 

[JD]

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.

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.

 

[Carl 1 Lucky Texan]

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.

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;
http://www.washtimes.com/business/20060808-124344-3187r.htm


Carl

 

[bigjim]

I have no problem with companies making $$ it is America after all. I
just choose to not add to their $$$ when not necessary. Personal
experience showed me that premium is not necessary so why bother.
People are free to spend more on gas. I won't and know that car will
run fine on regular and 'll save money

 

[Body Roll]

Thanks for the responses.

Is there anything I can do in terms of aftermarket modification (in addition
to driving conservatively) that will increase the cars MPG?

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.

 

[k. ote]

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.

You suck, troll.

 

[k. ote]

I have no problem with companies making $$ it is America after all. I
just choose to not add to their $$$ when not necessary. Personal
experience showed me that premium is not necessary so why bother.
People are free to spend more on gas. I won't and know that car will
run fine on regular and 'll save money

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!

 

[bigjim]

I would have no problems using regular in the STi . However I will
probaly not buy another. Prices are up and styling is just awful esp.

 

[k. ote]

I would have no problems using regular in the STi . However I will
probaly not buy another. Prices are up and styling is just awful esp.
on outbacks.

Yea you would. We both know you would.

 

[JD]

I would have no problems using regular in the STi . However I will
probaly not buy another. Prices are up and styling is just awful esp.

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