Regular gas in WRX

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

Reply to
Ron Olson
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Might find some discussion on this in the first few threads here:

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Steve

Reply to
Steve Jones

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.

R> Hi all-

Reply to
<brian

turbo-charged

Reply to
Edward Hayes

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 > Hi all-

Reply to
null

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

Reply to
Jim Stewart

Reply to
WRXtreme

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

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.

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

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

Reply to
CompUser

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.

Reply to
Byron

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?"

Reply to
CompUser

Reply to
Bryan Lee

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

Reply to
Ignignokt

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.

Reply to
Day

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

Reply to
Henry Paul

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).
Reply to
y_p_w

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.

Reply to
y_p_w

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

Reply to
Hallraker

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

Reply to
Henry Paul

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

Reply to
wavshrdrNOSPAM

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.

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.

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.

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."
Reply to
y_p_w

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