Regular gas for the US spec STI

[Philip Procter]

With gas prices skyrocketing, is there harm in using regular or medium
grade (89octane) gas in an STI for trips where you are careful to stay
off the turbo (much)?

Philip

 

[Greg]

With knock sensor technology you would probably "get away with it" but the
difference in cost over even a long trip is not a lot of money. Say you go
1000 miles and get 25 mpg, that's 40 gallons at 20 cents more per gallon for
an additional cost of $8 not even accounting for better gas mileage using
higher octane and better performance. Is $8 that big of a cost assuming you
can afford to take a trip in the first place?

 

[Edward Hayes]

I think it's foolish to drive using the knock sensor as the constant safety.
I would feed it the recommended gas and cut back on my driving miles. ed

 

[Bryan Lee]

That's a very bad ideal. You can damage your motor. I have a '04 WRX. If
you check your manual it says wrx must run a min of 91 octane and the STI
must run a min of 93. On all the WRX(sti) site people have tried to use
cheap gas in our WRX they all report a lose of on min 2 mpg and a lose in
power. Also the knock sensor only hears a knock after it happens. So you
will still damage the motor. I live out in Cali and we only have 91 octane
gas I add octane booster to every tank full just to give it that extra
margin. Turbo motors are very sensitive to quality of gas since they force
hot air into the motor they need help to control knock under boost. If you
use cheap gas all it can do is reduce timming and try to cope. You are only
talking a differance $1.50 a tank full(15g tank) . Is your car not worth an
extra $1.50 a tank. Depending on how you drive you should be getting around
22 +mpg on the highway anyway. I also have a '64 Pontiac Grand Prix that
has a 389 w/tri-power (three 2bbl carbs) that the manul says needs a min of
98 octane and recomends 100. I would drive to the compton air and fill up
with low lead 100 octane air fuel. At about $2.80 a gal for a 25 gal tank I
would spend about $70 every fill up. I was my daily driver that got about
maybe 10 mpg and would have to fill up every week. Finaly the EPA cracked
down and I could not get the 100 octance. So after have the car over 2yrs
and putting over 20k original(91k mi when I bought it now reading a little
over 110k). I pulled the motor and built it for unleaded and lower octane(91
oct and $5 a bottle oct booster). I went through all that trouble because
when I bought that car I know what it needed. So give your car what it
need. Isnt you car worth $1.50 a tank full?

 

[The_Incubator]

You'll probably end up getting worse gas mileage... I've found this to
be the case with cars that recommend higher octane fuel.

So you might hurt your engine without any savings to show for it.

Nick

 

[Carl 1 Lucky Texan]

Or switch to coffee instead of lattes and buy a water filter and lose
the bottled water. That will pay for your premium gas.

Carl
1 Lucky Texan

 

[Yousuf Khan]

With gas prices skyrocketing, is there harm in using regular or medium
grade (89octane) gas in an STI for trips where you are careful to stay
off the turbo (much)?

The knock sensor will probably prevent any major damage from happening to
your engine, but you will probably get *worse* gas mileage. The knock sensor
is an inherantly passive device, meaning that it waits for a ping to
actually happen before cranking back the timings, it doesn't proactively try
to adjust the timings. It'll keep your engine safe, but it won't make it
efficient.

Yousuf Khan

 

[Greg]

I was thinking give up fries with the Famous Star and switch to a medium
Coke at each fill up, but the thought is the same. I had connections with a
gas station at one time and it's amazing how people react when the gas
prices go up.

 

[John Emdall]

It is my understanding that 100 octane unleaded
(not avgas) is still available to the public at a
number of pumps in the so cal area. The only
caveat is they may not want to pump it directly
into your street car so bring a couple of 5 gal cans.

http://stevesnovasite.com/forums/showthread.php?p=26496#post26496

 

[Carl 1 Lucky Texan]

I worked in an oil-related field for 12 years ('logging' trucks for
those in the know). I will never complain about the price of oil.

Carl
1 Lucky Texan
(Please don't tell my Momma I work in the oil patch. She still thinks
I'm the piano player at the whorehouse.)

I was thinking give up fries with the Famous Star and switch to a medium
Coke at each fill up, but the thought is the same. I had connections with a
gas station at one time and it's amazing how people react when the gas
prices go up.

 

[Carl 1 Lucky Texan]

You could always investigate adding 1-2 gallons of toluene at each fillup.

Carl
1 Lucky Texan

 

[CompUser]

(e-mail address removed)>, (e-mail address removed)
says...

It is my understanding that 100 octane unleaded
(not avgas) is still available to the public at a
number of pumps in the so cal area. The only
caveat is they may not want to pump it directly
into your street car so bring a couple of 5 gal cans.

That's not the only caveat.

Avgas is *leaded*, so plan on replacing your cats
after a few tanks, too.

Steve

 

[The Vodkinator]

Okay, I'll ask the obvious question: why did you spend $30K+ on a
performance car like the STi if you don't want to spend the coin on premium
gas to protect your car's engine? The answer to your question is pretty
simple: use premium gas; don't screw around to save yourself a buck here and
there.

Jen
:: killing people and burning down trees :: http://www.stinkykitty.com

 

[CompUser]

Google "bore wash timing pinging" and decide for
yourself if this is a risk you *really* want to
take, to save a few bucks on each fill up.

Steve

 

[Dan]

Ok, let me explain about forced induction (turbo or supercharging) and
how it relates to octane ratings.
First of all the octane rating of gas is it's resistance to what's
called detonation. Higher rating=more resistance=better burn
When you're running any forced induction application this becomes
critical in that you start running a lot more air into the engine.
Remember, all that a turbo does is force more air into your engine so
that there is more air to burn. Now if you run any gas with too low of
an octane rating you are basically now running too lean on the engine.
It's just as if the engine wasn't getting enough fuel. Hence detonation.
Very bad juju. Too much air+not enough/wrong fuel=BOOM! Forget
knocking, we're talking about destroying your pistons, and blowing the
head on the motor. Trust me, this information came very painfully to me.

 

[Edward Hayes]

Right on Don: I've seen connecting rods outside the cylinder blocks bent at
right angles. Why would anyone spend 30,000 bucks and quibble about 5 bucks
more a week is beyond comprehension.

 

[Jim Stewart]

Right on Don: I've seen connecting rods outside the cylinder blocks bent at
right angles. Why would anyone spend 30,000 bucks and quibble about 5 bucks
more a week is beyond comprehension.

Want to hear a good one? My wife and I test-drove 2
wrx's at a local dealership. The first one drive like
a top but was the wrong color. The second one was the
right color, but in the showroom. They took it out
and it ran terrible. We left, not buying the car.
They called back and said it had been filled with
regular. They filled it with premium and give it
to a saleslady to drive around. We came back a couple
days later, test-drove it and bought it.

Damn near lost a $23,000 sale for a 1/4 tank of
regular gas.

 

[Chris Phillipo]

Subject: Re: Regular gas for the US spec STI
From: Dan <(e-mail address removed)>
Newsgroups: alt.autos.subaru

Ok, let me explain about forced induction (turbo or supercharging) and
how it relates to octane ratings.
First of all the octane rating of gas is it's resistance to what's
called detonation. Higher rating=more resistance=better burn
When you're running any forced induction application this becomes
critical in that you start running a lot more air into the engine.
Remember, all that a turbo does is force more air into your engine so
that there is more air to burn. Now if you run any gas with too low of
an octane rating you are basically now running too lean on the engine.
It's just as if the engine wasn't getting enough fuel. Hence detonation.
Very bad juju. Too much air+not enough/wrong fuel=BOOM! Forget
knocking, we're talking about destroying your pistons, and blowing the
head on the motor. Trust me, this information came very painfully to me.

The shortened version is; too low an octane with highly compressed air =
detonation while your piston is on the way up the cylinder. Snap,
crackle, pop!

 

[Mark Santa Ana]

The shortened version is; too low an octane with highly compressed air =
detonation while your piston is on the way up the cylinder. Snap,
crackle, pop!

I thought that was pre-ignition.

 

[S]

Hi Mark, All!

I thought that was pre-ignition.

Not quite, but same results. Detonation is where the air/fuel charge
basically explodes instead of burning with a nice even flame-front
pattern. It's caused by too lean of a mixture, or poor fuel (lo octane
or other). Pre-ignition is where you have a hot spot in the combustion
chamber that ignites the mix prematurely, causing excessive pressure
in the combustion chamber. That is caused by too hot of a spark-plug,
glowing hot carbon deposits on piston crown or combustion chamber,
etc. They _are_ closely related, however, Detonation frequently leads
to pre-ignition. It's a vicious cycle that can destroy an engine in a
few cycles.

ByeBye! S.


Steve Jernigan KG0MB
Laboratory Manager
Microelectronics Research
University of Colorado
(719) 262-3101