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Old 01-28-2005, 10:35 AM   #1
SilverRush
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Default Cobb Stage 2 with gutted exhaust

Has anyone tried simply gutting their downpipe with a catback exhaust and using Cobb's Stage 2?

I have a PDE catless downpipe and Cobb Catback and will be replacing the uppipe within the next month or two (probably with a gutted stock one). I have decided I do not want to run completely catless so instead of spending the money on a new catted downpipe I was thinking of gutting a stock downpipe and leaving the mid pipe cat in place. This would also be very stock looking which is a plus.

I have no plans of a turbo upgrade (will buy an sti before i do that) so I think the flat plate design of the stock downpipe should be sufficient.

What are people's thoughts?

Keith
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Old 01-28-2005, 10:50 AM   #2
SchnorrCS
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Let me know if you get a solid answere. I was wondering the same thing. I do know Cobb recommends a bell mouth design though.
If I were you I'd just call and ask Cobb. Straight to the source, ya know?
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Old 01-28-2005, 10:58 AM   #3
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I ran a gutted downpipe, a gutted 3rd cat w/ AP stage 2 for a few months. It did not throw any CEL and the performance was up from stage 1. Then I switched to the catless PDE downpipe and the power increase is very noticeable. Running the gutted downpipe with the stock 3rd cat will be fine but you'll be giving up some hp.
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Old 01-28-2005, 11:02 AM   #4
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car wont run great, boost target may be down. Just run a shorty dp with a high flow catted mid section.

Look at mad dads twin dump DP.
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Old 01-28-2005, 11:30 AM   #5
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The third cat will keep the noise and smell down, and only eats maybe 5 hp.
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Old 01-28-2005, 11:32 AM   #6
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I read on Cobb's tech forum a few months back that the only REQUIERED thing to do for stage 2 is the catless downpipe. The ecu will be able to compensate for the other things being stock. Straight from one of their techs.

BTW, the downpipe is the WORST cat to try to gut. The others are a cake walk in comparison. (I have done all three) Just so you know....

-Yergi
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Old 01-28-2005, 11:38 AM   #7
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Quote:
Originally Posted by whittleman
The third cat will keep the noise and smell down, and only eats maybe 5 hp.
10 hp 10 tq
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Old 01-28-2005, 08:12 PM   #8
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Quote:
Originally Posted by SchnorrCS
Let me know if you get a solid answere. I was wondering the same thing. I do know Cobb recommends a bell mouth design though.
If I were you I'd just call and ask Cobb. Straight to the source, ya know?
I did speak with Cobb and they said they recomend a bellmouth because it can build boost quicker. Anyone know why a bellmouth would build boost quicker? I would assume the wastgate is completely closed until the turbo is spoooled so why would any design make a difference over another design???
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Old 01-28-2005, 08:16 PM   #9
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Quote:
Originally Posted by kbui
I ran a gutted downpipe, a gutted 3rd cat w/ AP stage 2 for a few months. It did not throw any CEL and the performance was up from stage 1. Then I switched to the catless PDE downpipe and the power increase is very noticeable. Running the gutted downpipe with the stock 3rd cat will be fine but you'll be giving up some hp.
Ofcourse it won't throw a cel, the AP takes care of that. When you say the power was noticeable, how do you mean? Across the board, built boost quicker, up top.

I don't think the 3rd cat should rob much more than a couple hp.

Keith
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Old 01-28-2005, 08:19 PM   #10
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Quote:
Originally Posted by bren wrx
car wont run great, boost target may be down. Just run a shorty dp with a high flow catted mid section.

Look at mad dads twin dump DP.
Why do you think the car won't run great? Not disagreeing with you just want to understand.

Aren't all shorty downpipes flat plat designs? How are they any different then a gutted stock downpipe? Are they any wider?

I should of looked but does the stock downpipe completely uncover the exhaust on the turbo? If not then I will be coughing up the cash for a catted downpipe.

Keith
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Old 01-28-2005, 08:20 PM   #11
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Quote:
Originally Posted by yergi
I read on Cobb's tech forum a few months back that the only REQUIERED thing to do for stage 2 is the catless downpipe. The ecu will be able to compensate for the other things being stock. Straight from one of their techs.

BTW, the downpipe is the WORST cat to try to gut. The others are a cake walk in comparison. (I have done all three) Just so you know....

-Yergi
Not looking forward to it, however there are a couple for sale that have been gutted already.
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Old 01-28-2005, 10:16 PM   #12
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Quote:
10 hp 10 tq
At stage 2 power levels? Prove it
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Old 01-28-2005, 10:20 PM   #13
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Quote:
Aren't all shorty downpipes flat plat designs? How are they any different then a gutted stock downpipe? Are they any wider?
Most shorty DP's are not flat plate

Stromung is DWG, Scoobysport is belmouth, Bosal DWG

Oakos is flat plate.
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Old 01-28-2005, 10:32 PM   #14
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Here's something to mull over-

I have my uppipe cat in, and run a stromung DP with high flow cat.

I have a friend who has a catless uppipe, stromung DP and catless.

I've datalogged both cars (both '04s - stage 2) and we get the same exact spoolup. I would have thought that my turbo wouldn't spool as fast as his, but it does.

i can't wait to get the uppipe cat out to see what happens.

But we digress- I would think that running with gutted exhaust components would be okay, however, I'd think you'd get suboptimal performance. Cobb does say that performance may very depending on your exhaust.

I'd call them up and get their opinion and report back here

Mike
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Old 01-28-2005, 10:37 PM   #15
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I'm running a shorty belmouth DP, and I went to an exhaust shop the other day to see if they could make me a hiflo 3rd cat section to replace my oem 3rd cat. He told me it would be a waste of time and money. Modern oem cats are hiflo. They may not flow as much as a 3"metal substrate, but they are not as bad as everyone makes them out to be.

I also contacted a vendor on here about a hiflo 3rd cat replacement, and the response was you won't see much in gains, to paraphrase "6 hp with a catless piece, and less than 6hp with a catted piece".

If you get rid of the first 2 cats, the 3rd will not rob much power at modest power levels (stage 2).

Also, the only visible cat is the 3rd cat. Just in case someone needed to look under your car.
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