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Comments
-Frank P.
To be honest, it's difficult to proclaim that I've noticed any significant difference in performance. However, if I were blind tested, I do think I would be able to note a slight difference in power & 'smoothness' of power. Wouldn't put my life on that, though!
The performance of this vehicle just seems to get better w/the miles, so I may wind up using lower octane more often because either way, it beats the heck out of most anything else I've driven.
Also, consider the fact that the right octane will vary from vehicle to vehicle based on just some manufacturing variation quirk and enviromental factors.
I just read the C&D article on the Baja Turbo. They seemed very lukewarm to the product, espeically the concept of the Baja. Interestingly, C&D pointed out that the tranny didn't want to downshift while Edmunds review says it did.
Ken
corkfish: I also notice that - the Baja's tailgate is VERY heavy. Why? I swear the much bigger Avalanche's tail gate weighs half as much.
If you use 87 octane, I'd recommend gradually going down, maybe a tank or two of mid-grade inbetween. Let the ECU get used to it, dial back the timing a tad. I'd also avoid loading the engine really hard until it's had a tank full or two.
-juice
Bob
Hubby is out filling it up right now- I'll try to catch him....
Though- it's quater to half full, wouldn't it just mix anyway?
Long-Term Test: 2003 Subaru Forester
Steve, Host
Weening the car down thru a couple of tanks of Mid-grade won't help. You'll just get reduced output and increase the chances of knock.
If 91 octane really is the deal-breaker, you might as well get the XS. Between the XS and the XT on 87 octane, you might not see much of a performance differential.
I've driven the XT w/87 (several hundred miles) and the XS, and I can tell you there is no performance comparison. The XS is nice, but not even close in power/performance no matter what's in the XT.
I can't speak to theory, but that's a practical reality.
REALLY trying not to drive hard- but like other's have said, sometimes ya just can't help it!
I am grateful for the insight provided. Does it help to use 91 sometimes w/89 at times, and steering clear of the 87?
"Today's engines use highly evolved versions of a device called a knock sensor to adjust settings automatically for low-octane gas. And more engine control computers have adequate memory to allow separate sets of instructions for various octanes. The engine control computers keep pushing to maximize performance on whatever grade of fuel is used."
-Frank P.
This quoted from the above-linked article:
Extreme pressure inside the cylinders causes knock, which is the sound of the pistons literally rattling inside the cylinders. Too much too long can damage the engine. A little now and then won't.
But let's consider just what it is that turbos do, keeping in mind that "turbo" is a convenient truncation of the word "turbosupercharger":
The only modern engines that should really need premium are those with superchargers, which force-feed fuel into the cylinders. "You're driving along and just tramp the gas and the knock sensor cannot sense the knock fast enough in some cases," because the supercharger boosts pressure so fast, says Bob Furey, chemist and fuels specialist at General Motors.
Now my Saab (while I wait for my XT to arrive from the factory), can use 89 because the engine management system can compensate to reduce boost pressure based on octane sensors and the manual says either 89 or higher grades are usable. I cannot use 87.
The price for turbocharging is an increase in fuel cost. It's simply the way it works.
-les
I picked up my JBP 5 speed XT 3 days ago and am happy with it so far. I have no aspirations of great gas mileage with this vehicle.
Steve
Larry
You want nitrous with that?
Steve, Host
Other than that, the purpose of either is to cram a whole bunch more air into an engine.
Steve, Host
Ken
Is there anyway to turn off daytime running lights?
What is the bulb type for the fog light? It doesn't specify in the manual...
Thanks
Of course as has been pointed out, while it may seem painful to pay .20 extra per gallon, when you consider the additional annual cost vs total cost of ownership, the difference is pretty insignificant.
-Frank P.
http://auto.howstuffworks.com/turbo.htm
The following is an exceprt from the site:
With air being pumped into the cylinders under pressure by the turbocharger, and then being further compressed by the piston (see How Car Engines Work for a demonstration), there is more danger of knock. Knocking happens because as you compress air, the temperature of the air increases. The temperature may increase enough to ignite the fuel before the spark plug fires. Cars with turbochargers often need to run on higher octane fuel to avoid knock. If the boost pressure is really high, the compression ratio of the engine may have to be reduced to avoid knocking.
Hope this helps!
I would think that normally aspirated engine would get more out of it...
The intake on the WRX, for example, has enough capacity to handle a larger engine:
http://www.spdusa.com/stock_engine_mods.htm
It's probably similar on the XT.
You would probably get more improvement from a less restrictive exhaust.
Ken
Jim
are you going for after market one? If you don't mind me asking, where are you getting the estimates?
K
The specs and performance of the car are similar to the XT AT (3300 lbs, 222 hp, 221 ft-lbs of torque at 1800-5000 rpm). The engine runs great and uses a quart of oil every 3000 miles, up from not needing any oil between the 5000 mile oil changes. The original turbocharger is still running strong. We don't baby the car. For example, it is typically driven up a steep grade for several miles while the engine is warming up in the morning, and we take it to the mountains with a full load of passengers and cargo.
As cmuniz points out, the extra cost of premium gas is about $.01 per mile, or only $150 per year if you drive 15,000 miles a year. However, I figure that we saved over $1400 so far on our Volvo, which I think is a substantial amount.
My experience is that the experts are right when they say that using regular gas in an engine designed for premium does not hurt the engine, even for turbocharged cars.
Also, boost isn't as high as it is in the STi. So asking for the same octane as in the STi shows that Subaru is being conservative.
But.....the STi has had some detonation issues early on. I think Subaru resolved it, but I wonder if some owners were trying lower octane. That beast has such high boost that I would consider at least 91 octane mandatory.
Also, if the STi did have detonation issues even with Premium, it might be risky to use 87 on an XT, even with less boost.
For $150 per year, you could just play it safe.
-juice
In contrast, if there is potential for damage or greater wear, etc, then it makes sense to invest the $150/yr.
So the question keeps coming back to: Does it really matter? It would be nice to get some expert consensus on this, but I don't think we will anytime soon.
1) those who don't believe there's a risk, or are willing to take one.
and
2) those who will spend the extra to be "on the safe side" or perceive a performance increase with the higher octane.
I also don't think we'll get a clear cut resolution that will make everyone happy anytime soon.
Larry
From reading the USA-Today article, it sounds like the experts are all in agreement. However, as Larry pointed out, there are two diametrically opposed camps with neither likely to change their beliefs. Which is pretty much the same case as the dino vs synthetic or extended warranty debates :-)
-Frank P.
Now all I need to know is: On which side will I be???
As opposed to the ACTUAL reduction in performance -- as stated in the owner's manual -- when using less than 91 octane?
When the knock sensor retards spark timing, there is an immediate effect of reduced power, period. Not a whole lot of room for interpretation there, eh?
We can all politely agree to disagree, but let's get the factual elements of the opposing sides straight.
I'm confounded (and amused) by the number of people who choose a specific model based primarily on its performance characteristics (and are charged a premium by doing so), only to lament the cost of using the required fuel. Congratulations! You've just spent more money for performance you won't be getting on low-grade fuel!
So, I had settled on the Accord. Then I read the Car and Driver road test of the XT. Went by and drove it. The power shortage was fixed, and lo and behold, the kids could fit in the backseat. The stereo was excellent, whether playing Stevie Ray or David Lanz. And it had room for the monster Graco stroller. So bought it.
I am taking a hit on MPG. So far, at 700 miles, the best I am getting is 23 almost 24 MPG. With premium. And oddly enough, I don't mind the mileage or the premium fuel requirement. I am not going to split hairs that much, since I will also be using Mobil 1 for engine longevity. I can now carry my kids, have AWD, and lug the strollerzilla along.
The car is a big investment, and I want it to reach 200,000 miles. If it takes premium and only gets 26 MPG after it is broken in, I won't complain.
twrx
"Perceive: 1. To obtain knowledge of through the senses; to receive impressions from by means of the bodily organs; to take cognizance of the existence, character, or identity of, by means of the senses; to see, hear, or feel; as, to perceive a distant ship; to perceive a discord.
2. To take intellectual cognizance of; to apprehend by the mind; to be convinced of by direct intuition; to note; to remark; to discern; to see; to understand."
If someone perceives a thing to be real, whether its better performance or little green people from Mars, then that's the reality of their situation. Emotions and hard science don't frequently line up, IMO.
Speaking only for myself here, I believe there's little factual proof of why one car should make me (remember, just me, no one else) happier than another. There are other AWD, automatic, ABS, turbo cars out there to choose from. They all have their fans and detractors. Am I more right than other folks are because I bought a Forester XT and they didn't? My perception tells me I am. Someone else may perceive my perception as all wet. Free country, at least for now.
There is also nothing wrong with trying to get the most (pardon the pun) bang for your buck.
That's being frugal. Being cheap (and unwise IMO only) would be to ignore a preponderance of evidence that lower octane will either damage, reduce the life of, or degrade engine performance. Some people haven't satisfied themselves that that preponderance of evidence exists. They may also perceive the mfgr as being conservative in their ratings. Most good engineers do tend to be conservative in their ratings. So for people on one side of the equation, it's their money, and their vehicles they're willing to risk. Again, free country.
I personally fall on the other side of the equation. Speaking only for myself again, I knew when I bought my XT that Subaru said it required premium, so I run 93 Mobil. There is also nothing to preclude my perception from being factually valid. But, as someone else said "Perception equals reality" so maybe I just perceive it runs better on premium. :<)
Good to see you back, even in passing, Jack.
BTW - forced to admit I had to look up hubris, good one.
Larry
Himiler- Well that's one way to look at it. Here's another: Perhaps some folks feel the base engine's 165 hp just doesn't provide quite enough oomph but they don't really need all 235 lbs of torque available with the XT. They are therefore willing to sacrifice 12 lbs (5%) of torque, comfortable with the knowledge that they're still driving the fastest mini-SUV/sport wagon on the market. Therefore, if they're certain that burning less than premium won't hurt the engine, they're happy to save a couple of dollars at every fill-up.
To me it would seem that both camps should be satisfied. The one gets a high-performance Forester capable of wasting Porsches and the like and is happy to feed it the good stuff while the other is comfortable with the trade-off of a modest loss of power in exchange for the savings realized at every fill-up.
-Frank P.
Larry
John
26 mpg @75 mph
OK it is not as user friendly as the XT but the wagon is a good road car.
Larry or should I say Dr. Huxley ;-),
Can you please cite specific sources that support using 87 vs 91 octane will either damage engine or reduce engine life.
When I asked about using 87, SOA did not mention either damage or reduced engine life.
carlos castaneda (akasrp)
ps: shortlist: 04 V6 AWD Highlander, Forester XT.
pps: my correspondence with SOA:
Thank you for visiting the Subaru Web site and for your interest in Subaru products. The engine in the 2004 Forester XT is designed to operate using premium unleaded gasoline with an octane rating of 91 AKI or higher. Regular unleaded gasoline with an octane rating of 87 AKI may be used if necessary. For optimum engine performance and driveability, it is recommended that you use premium grade unleaded gasoline.
Thanks again for your interest.
Best wishes,
xxxx x. xxxxxx
Subaru of America, Inc.
-----------------------------------------------------------
YOUR ORIGINAL MAIL:
Hello Subaru,
Regarding the new Forester XT.
I understand the Forester XT uses Premium Gasoline.
What effects will using Regular (87 octane) gasoline have on the engine.
I am told all cars sold in the US must be able to run on regular gasoline.
The USA Today article is confusing at best. On the one hand, the auto and petroleum engineers are talking about how they use regular and don't see a problem, and on the other they specifically mentioned that supercharged (I would imagine includes turbos) engines need higher octane (though 89 was mentioned). It is also the case that several of the tuners for the WRX who sell ECU reflashes have specific maps for 91 vs. 93 octane, so it seems that higher octane can definitely give better performance, though clearly in stock form the safety factor is high and lower octane is probably safe.
I'd use 91 on a regular basis if it was common around here, but we mostly have 87/89/93.. The price diff. between 89 and 93 is minimal, and mixing to get 91 is a hassle.