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1999 Forester 'L'
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4 Posts
Discussion Starter #1
I recently purchased an 1999 Forester L with , 2. 5L, normally aspirated engine rated at 165-hp. I would like to add another 30-hp. Is this possible if a change the chip, air intake, and exhaust? If so, can you recommend any brands?

Thank you.
 

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Emeritus Forum Staff
2015 Triumph Tiger XCx 1 Down. 5 Up.
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5,242 Posts
I think you'd probably struggle to get 30bhp. 15bhp is more likely. Really, you need to change the cams in order to hike the power up on a n/a car.
 

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Premium Member
2007 XT Sport 5MT
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24,015 Posts
I don't know, you could get lucky with a those parts... but I'm not sure Subaru was all that conservative when they first tuned the 2.5 N/A engine.


As far as exhaust, go with a set of Borla replica headers from eBay, and then snag an Impreza cat-back to go with it. As far as intakes, there aren't too many out there for your application. Just about any intake for the 2.5RS Impreza (USDM 99-01) will work though.
Stay away from "chips" though, they're a joke when it comes to imports... and more often then not, the same reigns true with domestics.
See if you can get a local shop to do a custom tune for you, I believe there are some Subaru specialists in your area. Worst case, you could swap to the MY99 2.5RS ecu and get a custom tune since I'm pretty sure they will accept new tunes. I'm not sure the Forester ecu was reprogrammable for that model year.
Also, you should look into some other items to help reach your goals. You could get cams which would almost guarantee those numbers if you pick the right ones, but getting some intake and throttle body spacers will help a bit. Also swapping out for lighter pulleys will help you net some more power to the wheels at least.

there is some good reading in the 2.5NA subforum, as well as over on rs25.com
- 200 HP from a 2.5 n/a with just bolt ons?? - Subaru Impreza GC8 & RS Forum & Community: RS25.com
 

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Premium Member
2007 XT Sport 5MT
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24,015 Posts
I wouldn't rule out chips entirely as the 2.5RS guys seem to find they actually net more torque from the NA engine, but I still believe that a decent protune should work better than any off the shelf "chip".
 

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2002 Forester S
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270 Posts
I wouldn't rule out chips entirely as the 2.5RS guys seem to find they actually net more torque from the NA engine, but I still believe that a decent protune should work better than any off the shelf "chip".
+1 on the pro tune.

+1 also on the exhaust header, hi-flo cat and low restriction muffler. Also a low restriction air filter.

To make power you have to let it breath easy.
 

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2010 Legacy GT LTD 6 spd
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967 Posts
How about replacing the unequal length manifold on the older models mine is an (03) with the newer equal length design. That should add a few horsepower right? Enough to be a worthwhile mod?
 

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2001 SOLD!
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1,413 Posts
How about replacing the unequal length manifold on the older models mine is an (03) with the newer equal length design. That should add a few horsepower right? Enough to be a worthwhile mod?
Yes but you loose the Boxer rumble and you sound like any 4 banger out there. When I put my UEL Borla header, I got better low-end torque. For daily driving, I'll take low-end torque anytime.
 

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2001 SOLD!
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1,413 Posts
I am running a Borla UEL header with a custom fab 2¼" dia SS 304 welded to a Magnaflow. I also lightened my flywheel from 27 to 20 lbs. I match ported the intake manifold to the heads.

All in all, it helps and I have no clue how much I gained. Not dynoed yet and not expecting high numbers.

Next mods when I have time:

-Open up throttle body by 5%
-Fabricate a lightened crank pulley (got a lathe :biggrin:)


Maybe drop in an EZ30R or EZ36. Who knows LOL!!!!
 

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2005 Legacy GT
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3,679 Posts
If you are looking at intakes, you need one for a 98-99 2.5RS. Your car is MAF based so a 00-04 intake will not work on your car.

Like others have said, cams and a tune are the only real good way to add 30+ horses to an n/a. I had a full exhaust and CAI on my 99', and while the peak HP likely did not change a whole lot, the driveability and added torque (and better MPG) were good improvements IMO.
 
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