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I'm sure this has been covered before, but I couldn't find it in a search. I was looking back over an old issue of C&D with the story on the Forester 2.5XT when I came across something odd. I knew it was fast to 60mph(faster than all of the sports car convertibles compared in the same issue) at 5.3s, but they also rate it at 0-30 in 1.3s .... 1.3s!! Isn't that as fast or faster than the STI? I would assume that is due to less turbo lag and maybe shorter gearing? I was reading over the GT3, M3 CSL, and STI Spec C story someone had posted and thought I remembered seeing that the Spec C did 0-30mph in 1.5s

Anyway, I was wondering how much technology exactly was transplanted from the 2.5 sti motor over to the xt. I know the displacement and variable timing are there, but what else? They certainly extracted a lot of speed from that 210hp .. you'd think with another 90hp the STI would be so much faster, but it really is only nominally faster (in a straight line of course). I'm baffled!
 

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Well from what I've known about the differences it's as follows. Engine is the same minus the different turbo (the XT doesn't have the VF39), different ecu or at least tuning of it, and the drivetrain is different with the final drive at a different ratio. A lot of people are wondering actually if the final drive is actually hurting the XT in gas milage since it's ratings are quite low. As a side note, remember that the new Legacy GT will most likely have this same powerplant. It's not out of the ordinary for a car manufacturer to use the same engine in more then one model lineup they have yet have different hp outputs and even different drivetrain configurations. Take for example the 350Z and Altima/Maxima modes on the Nissan line. All the same engine yet different power outputs.

I for one have wondered what would happen if you swapped over the injectors (if different...) ecu and turbo from an STi over to the XT. I think tho that it's possible the engineers might have moved a few wires arround on the pinout just to mess with us. :)
 

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Ehh, wait a min.

Just a guess, maybe the XT hits 30 in 1st gear and the STi needs a shift to second to reach it? I don't remember where it redlines in first off hand.... But this is the reason the STi has decievingly high 0-60 times...
 

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my girl friend has the XT, only draw back is she opted for the AUTO :( but I like the car anyway I get to race a lot more against people with that then the blue rocketship :)
 

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The valve train is also different b/c XT does not have variable valve timing (what's the subaru acronym? I can only remember VTEC and VVTI).

I sincerely doubt the XT hits 30 in first gear. The main reason that the XT can get better performance numbers than the WRX is that the final drive ratio is so small, it's almost as if you've got a close ratio gear box, but no 6th gear. This means initial start is great and torquey, but when you're on the highway, your RPMs are pretty high, which would explain why MPG seems to be a bit lacking.

And yes, the Legacy is also supposed to have the same 2.5 block, but I think it will also be missing variable valve timing (maybe?). If you really want to test out the 2.5 blocks... i would think you might as well swap over the entire STi head (if you can find one).
 

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My guess would be that the XT's engine is similar to the STi's EJ257 minus the VF39 turbo.

Subaru VVT = AVCS, Active Valve Control System. The only model that has this currently, is the STi.

Definitely a different ECU tuned for more bottom end and higher torque than horsepower. That would explain the 0-30 times same as the STi...
 

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The forester xt is awesome. doesnt handle as well as the STI or Wrx, but will smoke somebody out of the hole as well better than the WRX. loud squalling tires on the turns. it is the same engine (minus red intake), computer set different, engine internals the same, variable valve timed, smaller turbo, smaller intercooler, 11.6 boost (vs STI's 14.5) shorter diff gears, and believe it or not less than 100 lbs more than STI! The main reason its so quick out of the hole is the smaller turbo spools faster than the VF39. It also has in the manual the continuous AWD like the WRX. The auto does suck though because it has the active AWD which is econo based due to 90% front 10% rear untill slippage. I sure smoked alot of cars when I drove the manual. The auto is quick too, but not quite the same. it likes to hesitate for gear choices, etc. Ill post more if anyones interested. a definite second vehicle for the ol' lady!!!
 

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new legacy is suppose to have a slightly different engine block to the STi and XT i read somewhere... it has AVCS too on GT model.

Edit: www.need-desire.com for anyone who hasnt seen the Legacy website.
 

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Might want to check on NASIOC, and the new Forester forums that got started recently. As I recall, it's all the same, including the AVCS, but the ECU is different.

I could be mistaken, but suffice it to say, the Forester could easily go over 300 hp as well.
 

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the XT is "rated" at 210...but dynos 10-15 hp higher than he wrx...and is faster than a stock wrx......

and it does have avcs.......same with the baja turbo.....

its a fun car......cant wait to mod one.....


i work at austin subaru by the way....down here in texas.....
 

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well, the XT dynos at 10-15 wheel horse power higher than the WRX... which could be accounted for by the smaller gear ratios... the crank HP may still be less than the wrx, although when it comes to performance, i guess WHP is what counts. But again, that's probably why the forester has lower MPG.
 

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Different tranny, different gears. Same motor. Different ECU.
 

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Gear ratio has nothing to do with how much horse power a car put to the wheels.


filbert said:
well, the XT dynos at 10-15 wheel horse power higher than the WRX... which could be accounted for by the smaller gear ratios... the crank HP may still be less than the wrx, although when it comes to performance, i guess WHP is what counts. But again, that's probably why the forester has lower MPG.
 

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I think it does. That's why simply changing the final gear ratio will make a difference in your quarter mile time. The power of the engine has not changed, but the power exerted where the rubber meets the road has changed.

An example is rock climbers. They have like 200-300HP engines, but they can achieve 1000HP at the wheels, simply by putting in a different gear box. But the sacrifice in having all this power, is that they can't go very fast.

If you think about it, I think this makes sense. I've had this conversation once before, but last time it just resulted in a flame war. I'd love to have an educated discussion and I'm happy to admit my error if you can explain why i'm wrong. I just happen to think it makes sense...
 

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No, they do not put out ANY more hp AT ALL. What they do put out is more TORQUE.

HP is energy output over time, torque is instantaneous output.
 

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SilverSTI said:
Gear ratio has nothing to do with how much horse power a car put to the wheels.
That's wrong. Torque is what is used to calculate HP. Torque "put down" can be changed by simply changing gear ratios. A 10 speed bike is a good example.

Remember that just because you get a smaller HP rating to the wheels doesn't nessaceraly mean you're making less HP at the engine. It matters on what gear ratios you use to transfer that power to the ground. Now I'm not saying that the XT has 300 hp, but just because of it's gearing it measures less, but gearing most certainly has to do with what is put down... "in each respective gear". <- this is why people do 3rd gear pulls in FWD cars on the dyno, but 4th on AWD cars to get a better measurement of HP to the wheels. If you don't belive me do a pull in 4th on the dyno then do one in 2nd. I guarantee you that your 2nd gear pull will have a higher HP reading.
 

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Wrong.

HP is output over time, and engine HP output doesn't change with gearing, because lower gears put out more torque but have to run faster to put it out - they're making the same power.


HP does not change with gearing, trust me.
 

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I didn't say HP changes with gearing. I said HP readout to the wheels changes with gearing. This is what we're talking about. If you're gona tell me that your HP reading to the WHEELS is the same in 1st gear as it is in 4th gear I'll tell you flat out you're on crack. I have a dyno pull to show you exactly that difference in readout per gear. If gearing has nothing to do with HP reading (or better stated how much work something is doing to move an object) then pullies (gears) wouldn't have been invented.
 

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i agree with jrsc.

When you drive, the pull in 1st gear is much stronger than 4th gear. That means your car is putting more force down on the ground which means the torque you are putting down is more in 1st than 4th. Since WHP is always calculated based on measured torque at the wheel, the WHP should also be more in 1st than 4th. But in all cases, the engine HP is the same.
 

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Jesus christ you guys....

NO, NO, NO, NO, NO.


If a dyno measures different HP in different gear it's a byproduct of the way you're making the reading.

Peak HP output is irrelevant of gearing. You get more TORQUE in lower gears, but OVERALL POWER OUTPUT is not bigger. It's putting out more torque at a lower speed.

HP, ALL HP, INCLUDING WHEEL HP, IS THE SAME IN ALL GEARS.

HP is total energy output. This increases with speed, that's why HP and torque curves cross at 5252 rpm.

The way the car pulls is different, the power output is not. The engine is always capable of putting out the same ammount of power at the same RPM, no matter what the gear.
 
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