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Comments
DaveM
overtime
The XT gas mileage issue depends entirely on one's perspective. People whose top priority is maximum performance think the XT's mileage is fine. Those of us who are disappointed seem to be in the minority.
Pure highway driving (70-80 mph) gets me 25 mpg consistently, with 3-4 tanks a bit higher than that in the 26-27 range - never less than 25 on 100% highway tanks yet. Believe it or don't, doesn't matter to me
I didn't look at the mpg figures at all when buying the FXT, performance was the thing for me. Needless to say I'm not disappointed in that department - the only change I'm looking at is wheels/tires, haven't decided if I'll wait another year or so until the OEM ones wear out. I'm thinking 225/55/17, slightly taller than stock - as the speedometer reads about 4% high right now they'll be just about right.
1) The rpm/mph ratio is identical for the XT/XS in 5th gear. Possibly there is an affect at lower speeds, but highway mpg differences are dramatic between the two engines;
2) Yes, tuning etc. compression, etc. power mode and so forth can all be summed up then as "less efficient".
John
As to your third point about compression ratio, I thought it should be the other way around. Note that FXT needs premium gas that dictates an at least 10:1 compression ratio....
Finally, I guess 25 mpg for FXT is unrealistic, maybe next time when you reported your MPG, you should also attach an analysis report on lead content in your local water...it doesn't just get into your head...it is also in your foot...
-Dennis
Those that may remember my initial posts recall my steering beam problems, which are not quite resolved yet. Another story.
All that being said, I've never had a regret about owning this vehicle.
Larry
True, because the XT/WRX 5th gear is taller than the X/XS, neutralizing the former's shorter final drive. However, in all gears except 5th, the XT engine is turning faster at any given road speed. So for any typical tankful of gas involving any driving at non-freeway speeds, the XT is still at a disadvantage, friction-wise.
john284: As to your third point about compression ratio, I thought it should be the other way around. Note that FXT needs premium gas that dictates an at least 10:1 compression ratio....
The XT needs premium gas NOT because of a high specific compression ratio (the XT's is indeed lower than the X/XS), but rather because the XT's maximum peak combustion chamber pressures while operating at high boost demand premium fuel to avoid detonation, even with its lower specific compression ratio. However, it remains true that its nominal compression ratio is lower than the naturally-aspirated X/XS, and that means that under normal non-boosted driving (meaning most of the time) the XT is at a disadvantage in terms of combustion efficiency. Ergo, poorer fuel economy.
If it weren't for the wastegate and the redline, you could potentially attain so much boost that the engine would literally explode.
So , the turbo spools up faster when there is demand for power, i.e. wide throttle opening.
BTW, the turbo is always on, except at low demand it spins relatively slowly, not producing much boost. Also, just because the gauge shows negative, doesn't mean you don't have boost, just means that the boost has not exceeded the vacuum. At zero on the gauge, the boost equals the vacuum, i.e. 1 atmospheric unit.
The cold-side compressor section is a pure centrifugal blower, meaning that the boost pressures rise with the square of rising impeller RPM. At moderate engine throttle (even at steady highway speeds) the turbo might still be idling along at relatively few RPMs, adding essentially no boost at all. Snap the throttle wide-open, and the impeller quickly accelerates to as much as 150,000 shaft RPM, driven by exhaust gas on the hot side.
Also, just because the gauge shows negative, doesn't mean you don't have boost, just means that the boost has not exceeded the vacuum. At zero on the gauge, the boost equals the vacuum, i.e. 1 atmospheric unit.
I define 'boost' as pressures exceeding what a naturally-aspirated (non-boosted) engine could register on a manifold gauge. A NA engine under WOT at moderate RPMs can come quite close to zero vacuum. Ergo, by my definition, the term 'boost' requires measured pressures higher than that - reaching into the above-zero range on the vacuum/boost gauge.
I think you're wrong. The specs for North American XTs are the same as the Australian ones. I don't have the CR numbers at my fingertips, but I believe the 2.5-liter XT/STi compression ratio is about 8.5 no matter which market.
Subaru calls that port the "ASPIRATOR HOSE", and says to check it do the following:
With the ignition switch to ON, push the “A/C” switch, set the temperature dial to maximum hot, set the air flow dial to “DEF” position, and fan speed dial to 4.
Put a piece of thread in front of the port and check that the thread moves towards the port indicating that air is being sucked into the port.
A permissible number to hold the thread from the port is 0.02 inches, which isn't much.
Sounds like they want the air coming in, just very weakly - I mean a "piece of thread". Don't know what the higher speed air you're forcing in will do to the life of the sensor, but I'm going to try it anyway.
I guess my main gripe with the auto climate control is that if its so flaky that its unusable under certain weather conditions,(some people seem to be having no problem with it, although they seem to be in the minority) is to save me the money and don't bother offer it. I mean I am paying for it on the sticker, one way or the other.
Larry
www.autoweb.com.au/id_SUB/doc_sub0308041/ cms/news/newsarticle.html
www.automotive.com/reviews/17/2004/subaru/ forester/25xs-premium/buyersguide/
http://www.caranddriver.com/article.asp?section_id=3&article_- - id=6854&page_number=4
It would be very unusual to not reduce an engine's compression ratio when adding a supercharger or turbocharger. This 8.2:1 value is, by the way, the same as the STi, because all internal parts between the two engines are identical.
http://autos.msn.com/research/vip/spec_engines.aspx?make=Subaru&a- mp;model=Forester&src=
-juice
As to the wide variations in mpg reported by different drivers, I gave up on trying to isolate why one person gets better mpg than another. There are just way too many possible variables. I do know that I've always gotten better than the EPA numbers on virtually every car I've owned so I'm assuming that driving style has to have something to do with it. Whatever the reason, I'm ecstatic with the last tankful @ 25mpg. I just hope I can keep it that high :-)
-Frank P.
Keep in mind most XTs are still very green. My mileage was 2mpg better at 15k miles than is was when new.
-juice
Or, maybe the new-car thrill wore off by then and you resumed driving normally instead of with a lead foot...
Good
-Great to drive (that says a lot)
-Price/Performance (again, a rare combo)
Bad
-Dash so poorly designed that speedometer is dark in too many lighting conditions. That is a pathetic design element.
-Ergonomics. I'm comfortable but....my leg is too close to the gas while my arm is too far from the top of the wheel. It doesn't come down far enough. Armrest (with and without extension) is a disaster
-Auto climate = Auto Irritant
So, my post is not overly wordy or specific. I think good speaks for itself. The bad is easier to specify and unfortunately a pretty big hit in my book. I never had a second thought about ergonomics in my honda. I'm trying to ignore them in my Forester.
Overall, it's a fun ride but not quite the perfect piece of machinery I would have liked...but that 2005 Legacy GT might be.....of course when I'm zipping up and down hills in San Diego the bad points don't matter as much. I'm headed to the mountains this weekend so I'll have more feedback later.
Anyone know of any mods to lighten up the speedo?
Agreed. Black-on-white would be much more readable in daylight than white-on-black.
Ergonomics...my leg is too close to the gas while my arm is too far from the top of the wheel. It doesn't come down far enough.
Definitely agree about the too-close gas pedal; when my seat's set for the right distance to fully depress the long-throw clutch, the throttle is too close for right-leg comfort. As for the steering wheel not coming down far enough, forgive the obvious suggestion, but have you tried raising the seat to the max? That's where mine is, and my steering wheel position is fine at about the middle of its vertical travel. I could move it farther down, but the rim would block the top of the speedometer.
Armrest (with and without extension) is a disaster
Agreed. How can it be so difficult to design a useable center armrest - right position, right height, and so forth? Maybe even itself adjustable.
Auto climate = Auto Irritant
It took me all of three or four days to give up on the automatic HVAC features and keep it in manual mode.
-Frank P.
I will tell you this, since I put that little fan over the senor, the cabin has become a total comfort zone, I haven't had to adjust anything on that climate control in 3 days.
I have a picture of this mod, but don't know how to post it here - does anyone know how?
Good for resale value :-)
Also agree on the throttle pedal position being too close when sitting so the clutch can be fully depressed. I've gotten used to it, same goes for the lack of a useful center armrest. When shopping for the FXT I also drove a WRX wagon - same issue with the clutch/gas pedal setup on it too, guess it's just a Subaru thing.
Don't have any issues with panel lighting, or steering wheel height - unlike Jack, I'm sitting fairly low.
Plenty of adjustment in all directions on the seat at least - unlike my wife's last two cars (Acura TL & Infiniti G35 Coupe), with power adjustable seats that don't go low enough to keep me from hitting my head unless tilting the seat back far more than I'd like.
http://www.imagestation.com/picture/sraid102/pe445e216ab91cb0cf4d- 7545b87c68732/f9b6a670.jpg
-Brian
I've now registered you on eighteen gazillion junkmail sources. Enjoy!
Reminds me of my dad's 'creative' improvements.
Don
Email Address Harvesting: How Spammers Reap What You Sow
Better to mark your email public in your profile, but no guarantees there either.
Steve, Host
http://www.nhtsa.dot.gov/NCAP/SList2.cfm
Can't wait for the warmer weather.....
Larry
By itself not a bad idea, but lets not make it a nonstandard mount.....
Dealer of course was clueless as they're handing me a blade assy with the hook attachment - "That'll fit your car" - "No it won't" - "Yes it will" - "No it won't" - you get the idea.
Now have one on order.
If anyone wants me to post the official part numbers, let me know either here or via e-mail in my profile.
Larry
I documented a 5 mpg AC hit when I drive home at the sweltering 105 degree temps we get here in summer. I did this by sweating for a week without AC and getting 28.5 mpg; with the AC on 50% time (no mornings, just afternoon) I get 26.0.
Keep in mind, auto-clim all the time = lower mpg.
John
It seems to me that if you get more efficient combustion at higher static compression, that is a good thing.
Can't the waste gate be set to keep over-compression from happening on the high end?
With premium "required", the static compression ratio for the turbo could be set even higher than the NA engine and still not have detonation problems.
John
That sounds like an anomaly.
I've charted my mileage for years, a short while ago I took averages for each season. Winter took the biggest hit, I average 2 mpg less than I do in Spring and Fall. Summer came with a 1 mpg drop in mileage, for A/C.
So reformulated fuels and cold weather actually hurt mileage more than having the A/C on all the time.
-juice
I am curious to see how it handles the new test.
overtime
John
-juice
Ballistic - if you're worried about the aesthetics, first, the black fan matches the black in the interior. Second, it can be spray painted any color you desire with spray enamel, Third, it's almost invisible in that little corner. Fourth, the benefit gained FAR outweighs any aesthetic considerations.
Larry - I tried to install the fan behind the dash and/or behind the sensor, but that requires serious cutting and butchering up of the internals. With the velcro, it can be removed in minutes without a trace and no cutting was necessary. If you do succeed though, I'm very much interested in how you wind up doing it.
Cheers
Disclaimer: I'm no combustion engineer; far from it.
Other things being equal, higher compression ratios are a good thing - but you can have too much of a good thing.
Compression ratios as high as (or occasionally even above) 11.5:1 have been used in naturally-aspirated production high-performance street engines. The combustion pressures produced at these lofty levels require the highest-octane fuel available to slow down the flame front and avoid damaging detonation. Alternatively, the spark can be retarded, but beyond a certain point this becomes counter-productive from an efficiency standpoint.
If an engine is to operate safely on lower-octane fuels, compression ratios necessarily must be reduced to prevent detonation.
Adding forced induction is precisely equivalent to raising an engine's nominal compression ratio. Therefore, for any specific octane rating, a forced-induction engine's compression ratio must be reduced; the higher the boost pressure, the lower the C/R must be.
The XT's max boost pressure is about 11.6 psi. This is almost 80% of one atmosphere, meaning that at max boost nearly 1.8 times as much air is being supplied to the cylinders than if the engine was naturally aspirated. Even with 91-octane fuel, the engine would detonate itself to death unless compression ratios were significantly lowered. If you divide an 11.5:1 high-performance NA compression ratio by 1.8, you get an equivalent forced-induction CR of about 6.4! The XT's 8.2:1 CR is actually on the high side.