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Old 01-31-2007, 02:23 AM   #1
Worxman02
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Question DP Question: Performance of catted shorty DP w/ high flow 3rd Cat vs. catted full DP

I'm trying to plan my next stage of modifications and I can't decide what route to go for when choosing a DP. I am concerned about the environment so I want to try to keep as many cats in as possible, but I don't really want to sacrifice performance too much. I really like the design of the 2 piece V2 DP from Daddy's SSCP as it allows me to have a high flow cat in the DP and then add another high flow cat to replace the OEM 3rd cat. However this is much more expensive than just getting one cat in the system and scrapping the 3rd cat. I was hoping that Daddy's could strike a deal with this set up as they told me that i could just order the DP half of their system w/o the 3rd cat eliminator. I just was wondering how much of a perfomance difference and emmisons difference would result from going with a DP like a catted COBB or Helix vs. a a shorty DP with the stock 3rd cat.

Oh and I have an STi Up-pipe, and 3" Borla XR-1 CBE as my current exhaust mods. Performance goal is close to 300 CHP.

'02 WRX

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Performance difference between Shorty DP w/ OEM 3rd cat vs. Catted Full DP
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Old 01-31-2007, 04:40 AM   #2
AlucardR
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My guess is it would cut your performance gains in half. If you have a catless setup...you're gaining around 20whp...and losing about 5hp with one cat, maybe more with a larger turbo. The performance difference wouldn't be so bad on the stock turbo, but if you upgraded to a larger one the two cats would be bottlenecks. Even one high flow cat is considered a bottleneck by some, when paired with a larger turbo.
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Old 01-31-2007, 07:39 AM   #3
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Quote:
Originally Posted by Worxman02 View Post
I just was wondering how much of a perfomance difference and emmisons difference would result from going with a DP like a catted COBB or Helix vs. a a shorty DP with the stock 3rd cat.
At typical 2.0L Stage 2 power levels, sticking w/ the stock third cat and using a shorty DP isn't going to be significantly more restrictive than using a full-length DP w/ a hi-flow cat. Yes, you'll leave a couple of HP and some torque on the table w/ the stock 3rd cat, but nothing you'll miss.

But, since you're looking to bump 300chp (which would be a fairly aggressive Stage 2 setup/tune), I'd suggest you go ahead and use a hi-flow catted DP to mate with your 3"CBE.

You definately don't need (or want) TWO post-turbo cats. One is just fine. And the difference in environmental impact is nill.

Last edited by Spenk; 01-31-2007 at 07:51 AM.
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Old 01-31-2007, 10:54 AM   #4
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When I bought my Maddad V1 Shorty Downpipe, Rich mentioned they'd dyno'd a 10 hp loss through the stock 3rd cat vs. their 3CE pipe. At stage 2 power levels.
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Old 01-31-2007, 01:14 PM   #5
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I had the exact setup you want, and ditched the DP because I felt I was losing too much power from having 2 cats, for not much gain. Now I have the Crucial DP, and MadDad 3rd cat, and I can definitely feel the difference between the two.
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Old 01-31-2007, 01:24 PM   #6
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Hey low: Just a note to mention we now offer catalyst replacements for the WRX/STi models. These include 3" plumbing, divorced wastegate, 304 stainless steel, etc that you expect from PERRIN. But now offered in upper and lower sections to suit your needs. In fact these may be considered legal replacements in states not requiring CARB EO#'s. (The catalysts meet or exceed EPA requirements for replacement catalysts. More information is available on our website.)

In regards to power, our 2007 STi show-car has twin cats on it (the same ones used in our catalyst replacement pipes) and with our 3076R .82 AR turbo kit is rolling 405 WHP with no water/meth, etc. That is running a street tune on 92 octane fuel. Properly chosen, high quality catalysts will not hinder performance.

Hope that helps. Let us know if we can help further! Thanks again!

PERRIN Performance
www.perrinperformance.com

Last edited by PERRIN; 01-31-2007 at 01:26 PM. Reason: Typos.
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Old 01-31-2007, 01:33 PM   #7
Worxman02
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Thanks for all the responses guys. I definantly will re-think my modification route.
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Old 01-31-2007, 05:11 PM   #8
pictureboy
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For what's it worth I made 295whp/275wtq with a shorty DP, my stock 3rd cat and a big 16G.
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Old 01-31-2007, 10:18 PM   #9
FromageTheDog
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No #'s at the crank, but you can (sort of) work it out. Here's my "stage 2" car with only the stock 3rd cat. Stinks to high heaven on startup, but once it's all warmed up you can't tell at all.

http://forums.nasioc.com/forums/show....php?t=1085868

The advantage with replacing the stocker with a high-flow metallic substrate cat is that the latter light off quicker. Flow better too...
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Old 02-01-2007, 01:43 PM   #10
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So it looks like the stock 3rd cat isnt really that much of a restriction unless your building a dyno queen.
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Old 02-01-2007, 04:31 PM   #11
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I will pass along my experience and you can make your own choice.
I had a bosal down-pipe (2.5") with the stock mid(cat) pipe and the SPT bosal single tip cat-back. VF22, pinks, UTEC, intake, headers, up-pipe, Big TMIC, etc. and put down 264whp 262ftlbs at 18 psi.

Later, I purchased an Injen downpipe (3" bellmouth) and welded in a 3" dynatech super high-flow cat near the rear flange. The results: 266whp 264ftlbs at 18 psi. Yep +2whp and +2ftlbs, thats all.

My brother in-law has a 2005 legacy GT with headers/up-pipe, intake, stromung dp (2.5"), stock mid(cat)pipe and a borla cat-back (2.5" to 2"). It put down 257whp 288ftlbs running the base Cobb stage 2 map. Another similarly modded stage 2 LGT with an Autospeed catted turbo-back exhaust (3" to 2.25") put down 251whp 277ftlbs on the same dyno, and it was tuned. Stock LGTs put down 190whp 220ftlbs. So, how much do you think his catted mid-pipe is hurting him?

I think you have to be pushing some serious power (350whp+) for the difference in pipe diameter and cat material to make a big difference. But my guess is that below 320whp your difference will be like mine, 2 whp 2 ftlbs.

Your choice.

Last edited by drwrx; 02-01-2007 at 05:04 PM.
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Old 02-18-2007, 12:52 AM   #12
wrx2k4blue
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Is the Stromung shorty DP really 2.5" The SPT/Bosal single-tip cat-back is 3" correct?
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