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Old 05-23-2004, 12:07 AM   #1
italy wrx
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Default up-pipe/downpipe torque loss

I installed a catless Perrin up-pipe/downpipe today and I have to say I am a little dissapointed in the results. It seems that I have lost torque up to 4500 rpm. Although I do notice a gain in pull from 4500 to 7000. It just seems to have lost the quick pull through the rpm range that it used to have with only the Greddy Evo cat-back. I did reset the computer, but it doesn't seem as fast. I was planning a computer reflash, but my friend (Subaru tech) says I should get quicker spool-up and noticable power gain from these mods. There are no MIL lights,and no exhaust leaks. Sounds great, but lack of torque makes me drive harder. Anyone have similar results?
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Old 05-23-2004, 12:36 AM   #2
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um.. I've never ever heard of that result.. losing the 3 cats should make a large torque & hp gain throughout the RPM band.. I think your butt dyno probably lies or is miscalibrated...

Unless you have a large exhaust leak somewhere (specifically the uppipe) these would cause big time power losses.
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Old 05-23-2004, 01:05 AM   #3
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Im going to check the up-pipe tomorrow, but wouldn't I get a check engine light for an exhaust leak?
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Old 05-23-2004, 04:28 AM   #4
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Quote:
Originally posted by italy wrx
Im going to check the up-pipe tomorrow, but wouldn't I get a check engine light for an exhaust leak?
No, not necessarly.
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Old 05-23-2004, 04:00 PM   #5
italy wrx
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No leak found at up-pipe to turbo, not sure about up-pipe to crossover(cant rev engine while under car, although I did stick screwdriver in bellcrank for t-body to hold constant rpm). I do smell exhaust fumes, and my up-pipe lost it's satin color(looks orange).
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Old 05-23-2004, 04:33 PM   #6
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Up-pipe leaks are pretty easy to identify, they make a very loud high pitched scream. You would know if you had one.

It's not uncommon for a loss in low end with a full 3"+ turbo back. Believe it or not, the stock turbo still likes a little back pressure to produce low end torque. EMS should help.
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Old 05-23-2004, 05:59 PM   #7
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I hear a "whistle" type noise, but it sounds like the turbo spooling up. I do have 3 inch all the way back(perrin catless d/p and greddy evo).
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Old 05-23-2004, 06:09 PM   #8
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Quote:
Originally posted by Cronos
Up-pipe leaks are pretty easy to identify, they make a very loud high pitched scream. You would know if you had one.

It's not uncommon for a loss in low end with a full 3"+ turbo back. Believe it or not, the stock turbo still likes a little back pressure to produce low end torque. EMS should help.
backpressure does not produce torque.
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Old 05-23-2004, 06:36 PM   #9
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Quote:
Originally posted by italy wrx
I hear a "whistle" type noise, but it sounds like the turbo spooling up. I do have 3 inch all the way back(perrin catless d/p and greddy evo).
It may be a downpipe leak, atleast thats what I associate the whistle with. Did you use new gaskets when you did the swap?
My buddy has a dp leak and it seems that his car doesnt pull quite as hard as mine.....makes that whistleing noise too. The loss of the up-pipe cat should definetely decrease spool time.

my $0.02
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Old 05-23-2004, 06:50 PM   #10
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You did said that you reset the ECU right.You gotta give it sometime for the ECU to learn,just like with everything else that has a computer in it..This has been covered so many time in this forum.Its not a leak.Give it about 3 days.
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Old 05-23-2004, 07:05 PM   #11
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I used all new gaskets(oem) and I did reset the ECU. I did a thorough and careful install and like I said could not find any leaks. Hopefully the computer will "learn". I'll keep driving it for a few days to see if it clears up, if not I'll start looking for leak.
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Old 05-24-2004, 08:06 PM   #12
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I think i've found the problem. On the Perrin downpipe, there is a seperate pipe to vent the wastegate. The piece of steel that divides the two pipes is holding the valve for that vent closed. I tried to move the rod from the diaphragm to the valve and it won't move. This, I believe is what is causeing my power loss issue. I will remove the downpipe and adjust the seperater and hopefully my problem will be eliminated.
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Old 05-24-2004, 11:46 PM   #13
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This problem sounds very familiar,this guy I work with had the same issues with the Perrin setup
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Old 05-24-2004, 11:58 PM   #14
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Could be since you went to a larger exhaust setup maybe it takes a second to spool up like it did on the old 2.25 pipes with back pressure? I know when I installed a 3" o2 housing and downpipe on my SRT it made a lil more lag but not much. Worth the gain up top though.

-melo
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Old 05-25-2004, 03:03 AM   #15
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no. The only time you may see slower spool is if your uppipe has a different inner diameter (larger) than stock.
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Old 05-25-2004, 07:51 AM   #16
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Sounds to me like a big plus for gutting the stock or going STI UP.
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Old 05-25-2004, 10:54 AM   #17
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I wonder if the 'loss' is because the wastegate spring is sprung a little too lightly - variation from the factory. For the stock setup it is fine, but when freeing up exhaust flow I think the wastegate spring occasionally needs to be tightened a couple turns to account for it.

With the light spring pressure, the wastegate flutters open earlier than normal and you get the low torque feeling down low.

Tom
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Old 05-26-2004, 03:38 AM   #18
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Problem solved! The perfrormance is awesome. The difference is night and day. I have quicker spool up and more torque. I'm so happy I figured this out, I was worried I made a huge mistake but I can honestly say, this was money well spent. Anyone installing this set-up should check the clearance of the wastegate vent before putting everything together and enjoy the results. Now all I need is an ECUTEK reflash and I'll be stoked!
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Old 06-04-2004, 07:55 PM   #19
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Quote:
Originally posted by mr. m
backpressure does not produce torque.
Oh young Jedi, much you have to learn.
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Old 06-05-2004, 07:41 AM   #20
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Quote:
Originally posted by Cronos
Oh young Jedi, much you have to learn.
Instead of just disagreeing, could you give us some explanation why you think backpressure produces torque?

I'm open to the possibility it may have some effect in the exhaust header, in NA engines... perhaps you can clarify.

However, I'm pretty sure that increased backpressure after the turbo will do nothing but reduce torque in all cases.

Why? Because it will definitely decrease the pressure ratio across the turbine, and therefore spin the compressor more slowly, putting less air into the engine. Less air=less gas burning, and less torque.
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Old 06-05-2004, 10:39 AM   #21
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Most good reflashes tune as a NA engine pre-spool (low rpms). That's why there is talk that a catless uppipe (less backpressure) reduces low end torque.
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Old 06-05-2004, 02:32 PM   #22
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I have only heard that a catless uppipe reduces lag. I have seen dyno plots where at no time do you make less power with the uppipe. That said, I have a ScoobySport catless TBE and SS UP, and it's great. Compared to stock, it felt like a stroker kit or something. I think my 2.5" exhaust is ideal for a 13G turbo. 3" exhaust on the stock turbo is overkill.
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