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Discussion Starter #1
So I got my OBX downpipe today, and for some reason I was under the impression (as listed in the description) that it was 3" tapering down to 2.5"

It's actually the opposite... I didn't know that >.<

So instead of sending it back and forgetting the whole idea, I ordered this:

http://www.summitracing.com/parts/WLK-41972/

I'm going to put it on and have it reduced about half-way down the vehicle to the 2.5". I have a decent muffler that I don't yet want to part with and this is my solution - seems legit :D Anybody want to chime in on this? Anybody else do something like this? :confused:
 

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...why would you want it to be 2.5". The FWD OBX downpipe that I helped my friend install on his S80 2.5T last night was 3" the whole way...same downpipe I had on my old 2008 2.5T S60.
 

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Discussion Starter #3 (Edited)
...why would you want it to be 2.5". The FWD OBX downpipe that I helped my friend install on his S80 2.5T last night was 3" the whole way...same downpipe I had on my old 2008 2.5T S60.
I was hoping that it would go with my current exhaust system... Like I mentioned, I have a nice muffler that I'm not willing to part with yet. I'm going to eventually get a nice 3" magnaflow or something like it, for now I'm going to keep it as is, and it will basically have a long stretch of 3" pipe before tapering back to 2.5" I'll post some vid with sound clips after the installation. Still waiting on the angled CEL and the little taper-er.
 

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Don't you think that's a little bit back asswards? Anyway, you don't think this would cause any problems do you?
I would hope that it was a straight 3" all the way through... (Like Stefan stated)

I don't know what the point of a high performance down pipe would be if it was as restricting as the stock set up?

What is the stock outlet size on the turbo?
What is the stock size between the DP and the exhaust pipe at the connector?

I have read on this forum and others that the OBX is straight 3 inch all the way through and if you hook that up to a straight 3 inch custom exhaust and you got some extra HP. In all my years I have never seen or heard of getting top performance by restricting the exhaust flow especially on a turbo charged vehicle.


Why is their so many varying size inputs on the forum, on the factory web site and eBay?
 

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Discussion Starter #8 (Edited)
I would hope that it was a straight 3" all the way through... (Like Stefan stated)

I don't know what the point of a high performance down pipe would be if it was as restricting as the stock set up?

What is the stock outlet size on the turbo?
What is the stock size between the DP and the exhaust pipe at the connector?

I have read on this forum and others that the OBX is straight 3 inch all the way through and if you hook that up to a straight 3 inch custom exhaust and you got some extra HP. In all my years I have never seen or heard of getting top performance by restricting the exhaust flow especially on a turbo charged vehicle.


Why is their so many varying size inputs on the forum, on the factory web site and eBay?
I'll at least gain the benefits of having a slightly less restrictive flow since the cat is gone, right? The stock size I thought was 2.5" - so wouldn't it be considered a slight improvement if any?
 

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Okay guys, so lemme try and straighten this out. Stock dp is 2.5'' all the way to the Cat(+-2.5"its weird shape and restrictive flow) then 2.5" to the exhaust coupler that is 2.5".

When you install a 3.5 or 3" dp, the couplers at the turbo and to the exhaust are still 2.5", otherwise you would not be able to attach it to your turbo or stock exhaust.
The gain of 3.5-3" is that right after the couplers the rest of the piping is that size, increasing flow.

If you decide to put a Cat in the system (possibly to avoid CEL without spacer, pass emission tests, avoid tickets for illegal exhaust, oh ya or the environment) you will slightly restrict the flow. To avoid the Catless "problems" most will install a 3" Race or Free flow CAT, so your legal and pass most emissions tests...
 

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Oh ya, you get more HP, the better the flow. That's why some don't stop at the DP but also do the exhaust to make it as free flowing with a 3" to the back....but in most states/provinces you need to have a resonator or other various exhaust components...Because it gets really loud...
 

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The angled flange turbo outlet on the mitsubishi TD04 series of turbocharges is 3", the straight flange on pre 2000 models is 2.5". The stock exhaust system is 2.25" if I remember correctly, my 3" straight through OBX FWD downpipe bolted right up to the turbo and stock exhaust system without any issues.

The OBX downpipe is 3" straight through, regardless of the misinformation on ebay.

Stock downpipe is 2" at it's narrowest point
 
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