Regular gas in WRX

[Ron Olson]

Hi all-

I have a 2002 WRX that I have been religious about putting premium in.
My brother-in-law scoffed at the idea of "requiring" premium and said
that the engine would run just fine on any grade. Whereas he
acknowledges that it would be better to use premium if we intend to keep
the car for a long time, he couldn't give a very good reason why.

So, my question: Can the WRX really use regular, at least once in
awhile, and what would be the long term consequences? And while we're at
it, what is the actual benefit of higher octane gas in the first place?
I know this might sound stupid coming from someone who owns this car,
but, well, there we are.


Thanks,

Ron

 

[Steve Jones]

Hi all-

I have a 2002 WRX that I have been religious about putting premium in.
My brother-in-law scoffed at the idea of "requiring" premium and said
that the engine would run just fine on any grade. Whereas he
acknowledges that it would be better to use premium if we intend to keep
the car for a long time, he couldn't give a very good reason why.

So, my question: Can the WRX really use regular, at least once in
awhile, and what would be the long term consequences? And while we're at
it, what is the actual benefit of higher octane gas in the first place?
I know this might sound stupid coming from someone who owns this car,
but, well, there we are.


Thanks,

Ron

Might find some discussion on this in the first few threads here:

http://tinyurl.com/4arsr

Steve

 

[Guest]

The owners manual is really clear on this. Your brother-in-law doesn't
understand the higher octane requirements of high compression, turbo-charged
engines.

The owners manual says you can run 87, when 91 is not available. I've been
tempted to try it, since I live at high elevation, and thus my compression
is lower.

 

[Edward Hayes]

You can run 87 only in emergences according to SOA. I presume that statement
is for legal purposes since you can get someone who is dieing to the
hospital or some other REAL emergency.

 

[null]

Yes you can run on 87 but power will be reduced and timing will be
retarded in order to prevent
preignition of the fuel and 'knock'. The high compression of the engine
will cause 87 octane fuel to pre-ignite
or pre-denote and that can easily destroy and engine. If you run 87 I
would NOT do any jack rabbit starts
or even moderately fast starts or 'goosing' of the gas peddle. If you do
you will get predenotation. Although
the knock sensors on the cam should detect this and retard the timing,
etc. to prevent this it's never perfect
and in the long run you'll most likely do some amount of damage to the
engine. If you can't afford the premium
then stick with a mix of premium and mid-grade. I ran 87 in my H6 once and
the performance was terrible and when
I did goose the peddle (just once) I got knock.

So your brother is partially right it will run on 87 but definately at a
disadvantage to what the engine
is capable of.

 

[Jim Stewart]

You can run 87 only in emergences according to SOA. I presume that statement
is for legal purposes since you can get someone who is dieing to the
hospital or some other REAL emergency.

I can tell you first-hand that a 2004 WRX will
run like crap on regular. Lookup my thread on
buying one.

 

[WRXtreme]

This is a very good explanation...except its "predetonation" not
"predenotation". Not trying to be nitpicky here, just want him to be able
to sound intelligent if he tries to explain it to someone else, and I
understand it was just a typo, it happens to all of us. (heh, it probably
happened to me in this thread)

 

[CompUser]

I have a 2002 WRX that I have been religious about putting premium in.
My brother-in-law scoffed at the idea of "requiring" premium and said
that the engine would run just fine on any grade. Whereas he
acknowledges that it would be better to use premium if we intend to keep
the car for a long time, he couldn't give a very good reason why.

"Well, it's better, but I don't really know
why"...heheheheh!

So, my question: Can the WRX really use regular, at least once in
awhile, and what would be the long term consequences?

The consequences would be more likely short term.
An extra couple of dollars in your pocket, and a
fat check for your mechanic or dealer, to rebuild
damaged engine.

And while we're at
it, what is the actual benefit of higher octane gas in the first place?

Reduces risk of engine destroying itself thru
pinging or pre-ignition.

I know this might sound stupid coming from someone who owns this car,
but, well, there we are.

Not at all. Go google pre-ignition and
detonation, learn the difference, then blow your
brother in law away by asking if there's a
difference...when he says "Nah, they're two name
for the same thing", tell him the difference.
Hahahahahah...wannabes, gotta love em...

Hey, where is that "Air Farce" Ranger, anyway??

Steve

 

[Byron]

The owners manual says you can run 87, when 91 is not available.
I've been

tempted to try it, since I live at high elevation, and thus my compression
is lower.

But when an engine has a turbocharger or supercharger, the lower air
pressure at higher elevations does not lower the compression ratio like
it does in a normally aspirated engine. The turbo just keeps packing
whatever air is necessary into the cylinders.

So if you have to run gas with an octane rating less than 91, I would
suggest staying south of the redline.

 

[CompUser]

This is a very good explanation...except its "predetonation" not
"predenotation". Not trying to be nitpicky here, just want him to be able
to sound intelligent if he tries to explain it to someone else, and I
understand it was just a typo, it happens to all of us. (heh, it probably
happened to me in this thread)

It did, actually in this post ;-)

It's neither "predenotation", nor
"predetonation"...it's pre-ignition, and
detonation!

Tho I have to admit I like the sound of that
predenotation...hmmm...maybe I'll try that at
work tomorow: "Are we sure they've all been
predenotated?" "Huh?"

 

[Bryan Lee]

Also you will lose 2 to 4 mpg. So what you save in gas on the price of gas
yu will lose in gas mileage and fun.

 

[Ignignokt]

Although
the knock sensors on the cam should detect this and retard the timing,
etc. to prevent this it's never perfect
and in the long run you'll most likely do some amount of damage to the
engine.

It's important to bear in mind that knock sensors can't *anticipate* engine
knock, and only retard engine timing *after* pre-ignition is already
occurring. It is therefore far better for your engine to run the
appropriate grade of fuel so as to *prevent* engine knock from occurring in
the first place.

A Google search of "pre-ignition" should reveal enough information about it
to discourage most people from running low octane fuel in engines not
designed for it.

- Greg Reed

 

[Day]

No. Don't even think about it. My previous car was an Acura Integra GSR
which takes premium gas. I tried put in regular and hard to start the car
the next day. OK after using premium gas. Regular gas might ruin your knock
sensor and internal engine parts.
One of the reasons I bought my 03 Forester XS is that it takes regular gas
whereas Turbo version requires premium.

 

[Henry Paul]

Predetonation? Isn't that when you pull the pin from a hand grenade??

 

[y_p_w]

But when an engine has a turbocharger or supercharger, the lower air
pressure at higher elevations does not lower the compression ratio like
it does in a normally aspirated engine. The turbo just keeps packing
whatever air is necessary into the cylinders.

So if you have to run gas with an octane rating less than 91, I would
suggest staying south of the redline.

1) The compression ratio is typically lower with a turbo'ed engine than
in an equivalent normally aspirated engine.

2) The octane demands will be lower at high elevations. The fuel
available in many high elevation areas contains lower octane fuel.
I wouldn't use it unless I knew I was going to be there for a
while.

3) Nothing can physically alter the "compression ratio" (which is
fixed), although the boost from the turbo does raise the pressure
(which some call compression).

 

[y_p_w]

It's important to bear in mind that knock sensors can't *anticipate* engine
knock, and only retard engine timing *after* pre-ignition is already
occurring. It is therefore far better for your engine to run the
appropriate grade of fuel so as to *prevent* engine knock from occurring in
the first place.

A Google search of "pre-ignition" should reveal enough information about it
to discourage most people from running low octane fuel in engines not
designed for it.

I thought detonation was a more likely thing to happen. Besides -
knock sensors are supposed to detect the **onset** of knock. It's
supposed to get more severe before it can cause engine damage.

And for "predetonation", I got in serious doo-doo with a nitpicky
guy who said that there was no such word, and that it was grammatically
incorrect.

 

[Hallraker]

Hi all-

I have a 2002 WRX that I have been religious about putting premium in.
My brother-in-law scoffed at the idea of "requiring" premium and said
that the engine would run just fine on any grade. Whereas he
acknowledges that it would be better to use premium if we intend to keep
the car for a long time, he couldn't give a very good reason why.

So, my question: Can the WRX really use regular, at least once in
awhile, and what would be the long term consequences? And while we're at
it, what is the actual benefit of higher octane gas in the first place?
I know this might sound stupid coming from someone who owns this car,
but, well, there we are.

A friend of mine had a mid 80's Thunderturd Turbo Coupe. I remember there
being a switch on the dash that allowed him to change between regular and
premium fuels. I remember asking him about it, and he claimed that the
difference between the two settings was "noticable" with the proper fuel in
the tank on each setting. Also, switching to the wrong switch position made
the car run like "crap" according to him.

Since this was the 80's and electronics weren't as sophisticated as they are
20 years later, I would dare guess that they aren't as tolerant of the
"wrong" fuel. So for me, if I had a brand new WRX, you can bet your Subie
that I wouldn't be putting anything less than premium in it. (Because,
honestly if I had the money for such a Soob, I wouldn't care as much about
the extra couple dollars.)

My '95 Outback has a slight hesitation problem with certain brands of fuel
of the regular variety. I did run premium in it for a while before the
$2.00+ a gallon in these parts, and while the vehicle seemed much more
responsive to the go pedal, I deemed the extra cost unworthy when local gas
prices soared. I've managed to find a few stations that seem to produce
"hesitation free" regular fuel, and so I just go to those stations when
possible.

Ultimately though, I suppose you could put regular in if you had some reason
to. But if you did that, I'd go light on the throttle and try to keep the
boost off.

-Matt

 

[Henry Paul]

That defeats the whole purpose of having paid the extra $$$ for the turbo
model in the first place.......

 

[Guest]

Lets break some of this down. My BS detector has been going full bore on a
lot of this.

1.) Will running lower octane fuel in your car make it harder to start? NO!
This is a wive's tale.

2.) Why is detonation bad? Because the increased PRESSURE due to combustion
taking place before (TDC) TOP DEAD CENTER of the piston's travel up and down
the cylinder can stress the connecting rods, sometimes bend a rod, cause
crankshaft problems or (most commonly) pound the ring lands on the piston
until the fracture and then your piston ring shatters and scratches the
bejezzus out of the cylinder and the metal shards goes out the exhaust valve
hopefully without to much damage.

3.) High altitudes effect on compression ratios and octane requirements.
Higher altitudes DO lower the OVERALL effective compression ratio even in a
TURBO car but NOT to the extent that normally aspirated cars will notice it.
The only exception to this is IF the boost control system is REFERENCED to
ABSOLUTE pressure rather than atmospheric. Most boost controllers are
referenced to atmospheric rather than absolute. There is also a direct
relationship also with temperature and altitude. Higher temps and altitude =
less dense air = less OVERALL effective compression ratio = lower
performance (usually). SO... you could run lower octane fuel at higher
altitudes with less detrimental effect. Still wouldn't suggest less than 89
octane in a turbo subie. Mine detonates on 93.

4.) Fuel mileage will not go up 2-4 mpg if you run 93 vs. 87 octane. This is
PURE BS! The extra octane ONLY comes into play at high boost and load
conditions. At normal cruise, i.e. 70-80 mph the subie motor could run on 85
octane without much issue. Another way to suppress detonation is with water
or alcohol injection.

5.) Lower octane fuel actually has a HIGHER energy content than higher
octane fuel.

6.) Based on #4 above, if you drive mostly highway and rarely accelerate
hard, you can easily and SAFELY run lower octane fuel. If you like
performance like me, you will always be hunting done the race gas to improve
the performance IF and WHEN you have the mods to truly take advantage of it.

7.) Higher octane allows you to run more ignition advance which gives you
better throttle response and efficiency but only up to a point. It also
allows you to run more boost assuming you have the mods to take advantage of
it. Hi boost with a lot of ignition advance is a sure recipe to invite knock
(pinging, detonation, etc.). This is the ENEMY of turbo and supercharged
motors. Left unchecked it can destroy your motor in a half second or less.

8.) I could go on and on about this but hopefull you get the idea.

Tim

 

[y_p_w]

Lets break some of this down. My BS detector has been going full bore on a
lot of this.

5.) Lower octane fuel actually has a HIGHER energy content than higher
octane fuel.

Don't know about this. I've heard the energy content of fuel can be
variable depending on any number of conditions. Winter fuel and
oxygenates might have an effect. If there is a difference, it'll
be neglibible.

6.) Based on #4 above, if you drive mostly highway and rarely accelerate
hard, you can easily and SAFELY run lower octane fuel. If you like
performance like me, you will always be hunting done the race gas to improve
the performance IF and WHEN you have the mods to truly take advantage of it.

True to an extent. However - I drive up a 20% grade on a regular
basis. Going up a steep hill requires "adding energy to the system"
as does accelerating on flat ground. The Volvo in front of me today
maxed out at about 20 MPH for a short time.

7.) Higher octane allows you to run more ignition advance which gives you
better throttle response and efficiency but only up to a point. It also
allows you to run more boost assuming you have the mods to take advantage of
it. Hi boost with a lot of ignition advance is a sure recipe to invite knock
(pinging, detonation, etc.). This is the ENEMY of turbo and supercharged
motors. Left unchecked it can destroy your motor in a half second or less.

I thought that's what the knock sensors are for - i.e. to detect the
onset of knock before it kills the engine. Most manufacturers say
that a mild amount of knock on hard acceleration or going up hills
is normal - I have my doubts. That being said, it sounds like
knock sensors are a very good idea.

8.) I could go on and on about this but hopefull you get the idea.

Forgot one thing. I'd put the way cars that should use premium fuel
under the following categories:

1) "Normally requires premium" but will take regular with reduced
performance. This language is usually attached to performance
cars.

2) "Uses regular" but will have added performance with premium
fuel. This language goes with family cars, like a Toyota
Camry V6.

This is from the manual for a 2001 Toyota Camry.

"1MZ-FE (V6) engine: Select Octane Rating 87 (Research Octane Number
91) or higher. For improved vehicle performance, the use of premium
unleaded gasoline with an Octane Rating 91 (Research Octane Number
96) or higher is recommended."