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Old 11-16-2012, 01:03 PM   #1
MoRex
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Default jdm v7 sti Down-pipe question(s)

Hey folks, i'm wondering if there's any downfall to snagging a complete V7 STi exhaust incl. catted downpipe and getting it tuned as opposed to going with something north american (cobb, etc.)

I prefer the 'quieter' STi exhaust, fwiw. More inquiring about tuning and hp in the end.

This is for a 2003 wrx wagon, and i do not plan on taking this car beyond stage 2.
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Old 11-16-2012, 03:07 PM   #2
kayen
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You can't really go beyond Stage 1 with a Stock Exhaust Setup. Stock Downpipes with the Catalyst are very restrictive. If you ever want to free up some power you need to get an Aftermarket Downpipe with a Hi-Flow Catalyst and if you want to keep the noise down you can run a stock Cat-Back system, but will lose some potential HP.
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Old 11-16-2012, 03:14 PM   #3
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Just to clarify, the stock jdm STi v7 downpipe's cat is considered restrictive in comparison to say, a cobb catted downpipe for an 02-07 wrx?
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Old 11-16-2012, 04:59 PM   #4
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A V7 downpipe is going to be similar to a US WRX or STI factory downpipe, and they are all very restrictive.

An aftermarket catted downpipe is going to flow way more than a factory downpipe.
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Old 11-16-2012, 07:09 PM   #5
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Thanks for the clarification.
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Old 11-18-2012, 07:44 PM   #6
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v7 downpipe is virtually the same design and diameter as USDM, just cut into a different number of pieces and 1 fewer cat. IIRC the midpipe may be 0.25" bigger in diameter. but it will make hardly any difference and will not get you to stage 2.

get an aftermarket downpipe, it makes a huge difference and won't increase sound as drastically as an aftermarket catback. the only aftermarket catback I've heard that comes anywhere near stock sounding is Fujitsubo and they are pricey. Prodrive is NOT. Maddad Whisper maybe but I haven't heard one.
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Old 11-18-2012, 08:43 PM   #7
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i'm not really interested in changing the muffler. Was more just inquiring because of the substantially lower cost of the entire exhaust (dp, mid, muffer) vs an aftermarket catted DP alone.
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Old 11-18-2012, 08:53 PM   #8
D-Rodman
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The most cost effective way to go with an aftermarket quality down pipe is something like a stromung shorty. You'll bolt your stock 3rd cat to it and off you go. You can find them on the used market for very reasonable money. You can also buy a cheap down pipe on fleabay.
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Old 11-18-2012, 09:29 PM   #9
bluestone
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In that case, go with the ERZ/CNT catted downpipe. It's a full 3" with a bellmouth. Much more flow than a shorty + 3rd cat. I had a Bosal (same flat flange design as Stromung) and switched to the ERZ. The cat is effective at passing smog and cutting down noise and smell. And it's cheap. I was closer to failing smog with only the stock 3rd cat v. ERZ.
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Old 11-18-2012, 10:08 PM   #10
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no concern about Smog here. We do not have it. More concern about smell / noise of catless DP (more smell than anything).

i'll atleast look into ERZ.

In all honesty though, i'll probably just go with a Rocket Rally catted DP, as they will be tuning, eventually.
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Old 11-18-2012, 10:35 PM   #11
D-Rodman
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That erz cnt down pipe looks good and the price is reasonable, you'll need the $30 adaptor if you are running a factory like donut style intermediate pipe. That takes you into the $400 range. A high flow exhaust with a factory 3rd cat may cost you 5% in power loss. Say 300hp with full high flow exhaust or 285hp with the slight restriction of a factory 3rd cat on an otherwise high flow exhaust system. If you ever plan on going with a bigger turbo and higher hp you definitely want the bellmouth full length down pipe. If you are just going stage 2 for improved driveability keeping your stock td04 turbo, you'll be just fine with a stromung shorty for $169 and bolt your stock 3rd cat to it. I have a stromung shorty on my 05 saabaru with the stock 3rd cat, stromung 2.5" intermediate and a prodrive 2.5" oval axleback runing on Cobb stage 2 for several years and it is a very torquey exhaust. You can run a 300 hp wrx on a 2.5" exhaust. Look at the oakos project bugeye for example. I've had a full Cobb turbo back on my saabaru before the current setup I mention above, if there is any loss it isn't even noticeable. I did however feel the difference in stronger torque at low rpm's with the stromung shorty, the divorced wastegate design works rather well and never had boost spiking or any monkey business.
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