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Old 07-05-2005, 02:39 PM   #1
Scooby Newbie
Member#: 65165
Join Date: Jun 2004
Chapter/Region: MWSOC
Location: Fayetteville AR, USA
97 OBS
i miss my RS...

News NEED IMEDIATE INPUT!!! (please)


I just put a prodrive oval tip axelback from a wrx(2.5") on my NA 2.5rs with a custom 2.5" center pipe(eliminating the after-cat resonator). 2 problems!!

1. Low end torque! where'd it go!?? I don't care what anyone says, The 2.5 is TOOOOO big, feels fantastic above 4000 but there's no pull below 3500!

2. WOW this is pretty loud. Not so much when cruising above 35mph but from a standstill it sounds like I'm lining up to race... EVERY TIME. haven't caught the attention of any PD yet....I just moved here, what does it take?


I have an appointment to have a 2.25 pipe made, using the old resonator right after the cat. GOOD??
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Last edited by darkwaterz; 07-05-2005 at 06:57 PM. Reason: RESOLVED!! check it out!
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Old 07-05-2005, 02:56 PM   #2
Scooby Newbie
Member#: 79527
Join Date: Jan 2005
Location: Christian's Mecca, CO
2005 2.5RS(I NDTRBO)
Chipped Crystal Gray


2.5 too big, huh?

Damn, That is what I was planning on. I've always had good luck with 2.25, though.

Your plan sounds good, Let us know the results.
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Old 07-05-2005, 03:14 PM   #3
Scooby Specialist
Member#: 51642
Join Date: Dec 2003
Chapter/Region: TXIC
Location: San Antonio, Texas
2001 Impreza RS


Originally Posted by darkwaterz
I have an appointment to have a 2.25 pipe made, using the old resonator right after the cat. GOOD??
That's what I did from the get go. I used a custom 2.25" midpipe to a WRX axleback. Increase in sound with little to no change in performance. Maybe a little above the 4000rpm mark.

Possibly any leaks? That will kill some low end torque.

For an inspection I had to take my borla headers off (larger diameter ~2.25 infront of the converter). And I noticed that when I put them back on I definitely had more low end over stock. I also have a ganzflow intake, so I got more flow in matched with the increase in exhaust flow.

Did you reset the ECU? Never hurts. GL!
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Old 07-05-2005, 03:41 PM   #4
Scooby Newbie
Member#: 84885
Join Date: Apr 2005
99 2.5 RS


I just got done doing a bunch of upgrades to my 99 RS. I started with the cat back and noticed the same thing. I used a 2.5 cat back and noticed a little low end disappearance, but when I installed my COBB CAI, it evened things back out, with a lot more pull across the entire band. You may want to look into a CAI. Also my cat back seemed really loud compared to stock until I put the headers on, now itís more of a rumble and less of a high pitched rev. I say pick up some headers and a CAI, you will notice a big difference.
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Old 07-05-2005, 04:26 PM   #5
Scooby Specialist
Member#: 67247
Join Date: Jul 2004
Chapter/Region: Tri-State
Location: UAlbany - Brooklyn
2003 2.5RS BRP
SQC 189


too loud could be exhaust leak!
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Old 07-05-2005, 04:57 PM   #6
Tim Sanderson
Scooby Guru
Member#: 6486
Join Date: May 2001
Chapter/Region: MWSOC
Location: S.E. wisconsin
00 Impreza 2.5 RS
Blue Ridge Pearl


Darkwaterz, Do you have any other mods?
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Old 07-05-2005, 05:10 PM   #7
Scooby Newbie
Member#: 89912
Join Date: Jun 2005
Location: ontario
2005 Impreza 2.5rs
Inexplicably rusting.....


Originally Posted by Impreza2003
too loud could be exhaust leak!
yeah, that happened to my '91 MR2 and it ws a gasket
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Old 07-05-2005, 05:28 PM   #8
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Member#: 88219
Join Date: May 2005
Chapter/Region: SCIC
Location: Nor Cal
1992 Legacy SS
EJ22t + 16g = :)


Its because on N/A engines you have to even out the circulation of gases. In your case the exhaust is able to be pushed out easily but the intake air cannot go in as fast. I would suggest doing what mc_866 did and get a good CAI to even out the air flow.\

As for headers you can't go too big or you will lose the backpressure that N/A engines need to help pull exhaust out of the combustion chamber. Go to Unabombers manifesto and go through the Exhaust section. There are 2 links, one goes to Cobb's website and one goes to Vishnu tuning. Read the parts more N/A engines and maybe it will make more sense
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Old 07-05-2005, 06:51 PM   #9
Scooby Newbie
Member#: 65165
Join Date: Jun 2004
Chapter/Region: MWSOC
Location: Fayetteville AR, USA
97 OBS
i miss my RS...

Cool Resolution!

first off, thanks for the quick feedback, I was checking it frequently before my appointment.

This is what I did:

I reset the ECU...That actually did help a bit, but not to my satisfaction.
I had the guy remove the front gasket at the weld and the rear gasket a few inches from the weld, he attached the resonator up front and followed it with 2.25 tubing. The 2.25 overlapped(or underlapped ) the small piece of 2.5 and welded at its end so that when I want to go back to a 2.5 all the way through(like when I go EJ20t), I can just cut it at the weld and take it from there.

SO, The sound is a little tiny bit quieter when cruising and alot softer from a stand still....still roars like a beast when I punch it. AND>>> I HAVE MY TORQUE BACK!!!!!!!!!!!!! It may still be a bit gentler real low(can't really tell) but it definately feels improved over stock above 4000...(but not as much as with the 2.5)

You're right, I do need to invest in the CAI for power AND balance, Cobb sounds good if it works with that stupid MAF.

Thanks all.
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Old 07-05-2005, 10:12 PM   #10
Scooby Specialist
Member#: 40337
Join Date: Jul 2003
Chapter/Region: BAIC
Location: Bay Area
95 L Coupe Swapped
99 Outback


You must be smoking crack, because i sure didn't lose and lowend torque with my 2.5in cat back. You have to reset the computer and give it a whole tank of gas to really learn your "not stock set-up". But i also have intake too.

Fine, maybe at idle up to 1500 rpms there is less power then stock. I can say for sure there is more torque at 2500 rpms with 2.5in.

Last edited by RS_to_WRX_swap; 07-05-2005 at 10:17 PM.
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Old 07-06-2005, 06:55 PM   #11
Scooby Specialist
Member#: 14365
Join Date: Jan 2002
Chapter/Region: RMIC
Location: Lakewood, CO

Yeah... need an intake too and a computer chip of some type would help... otherwise the exhaust doesn't have enough flow or the right fuel ratio to really work well. As far as volume you could get the midpipe resonated to cut the sound down a bit.
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