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Old 03-17-2013, 02:18 PM   #1
maizer89
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Default going from a 2.5 to 3" dp

hey this may appear like a noob question but I thought it doesn't hurt to shoot this question up on the boards. I have a 2010 wrx and originally planned to keep my catback stock so I got a cobb catted downpipe that tapers to 2.5in when it meets the midpipe, but now after upgrading to an invidia q300 3in exhaust, I'm contemplating switching to an invidia 3in downpipe to match. So my question is when upgrading from a 2.5in cobb downpipe to the 3in invidia dp is there warrant for a retune? TIA
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Old 03-17-2013, 02:29 PM   #2
RoadKillDMD
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What kind of engine management are you running? Do you plan on getting a catted or catless downpipe? People think because of the taper, the Cobb DP is going to be more restrictive. That is a misconception. You won't gain much if anything at all by switching to a full 3" DP campared to your Cobb DP. So to answer your question, generally no. You won't need to retune your car. Unless you run into boost creep/boost spike issues from running catless, your current tune should be fine (assuming you are actually tuned for the DP).
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Old 03-17-2013, 02:44 PM   #3
maizer89
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I had a open source pro-dyno tune with the cobb catted dp and the stock exhaust, so with adding the q300 exhaust and switching out to a 3in invidia catted downpipe I probably shouldn't worry about a tune right?
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Old 03-17-2013, 03:58 PM   #4
GrumpyPitbull
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Quote:
Originally Posted by maizer89 View Post
I had a open source pro-dyno tune with the cobb catted dp and the stock exhaust, so with adding the q300 exhaust and switching out to a 3in invidia catted downpipe I probably shouldn't worry about a tune right?
Well, the downpipes are different other than the taper. Cobb uses a belmouth design and Invidia uses divorced. How this will effect youe tune, I don't know ... Never tried it myself.

My guess is that the tune will be off since the flow will be different, but you won't know till you log it.
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Old 03-17-2013, 09:00 PM   #5
andrey64
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Even if one is bellmouth and another is divorced you should not run into a massive issue. If your getting a 3 in catted invidia it will be roughly the same as your cobb.

Your protune will work but not as efficient as for the cobb dp. Call up your tuner and ask him if he can look over the car and double check if there's any issues in the logs.
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Old 03-18-2013, 07:55 PM   #6
mechatricity
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Won't matter a bit. 3" catted DP is a 3" catted DP. The breathing room is needed up near the turbo, hence the "bellmouth." The invidia DP is also "bellmouth" it just has a divorced wastegate section that plumbs back into the pipe downstream.
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