ZachCouch Posted April 4, 2018 Share Posted April 4, 2018 I've read in several threads across the forums that if you replace the downpipe in a Legacy GT/ Outback XT, whether catted or not, a tune is absolutely required. What kind of tune would be needed? I've also read that it isn't necessary to tune after replacing the up-pipe or mid-pipe cats. Why don't they require a tune? It would seem to me that they'd all be equally important, why is the downpipe one so special? I'm getting a P0420 emissions level code on my 2005 Outback XT. I'm going to replace the rear O2 sensor tomorrow. If that doesn't fix the code (hoping it will), I'm gonna look into doing some exhaust work. I'm thinking of doing an Invidia catless up-pipe, Cobb catted down-pipe, and probably an Invidia catless mid-pipe. All that is still cheaper than a new downpipe from Subaru. A slight performance increase for less money seems like a no-brainer. Even if the O2 sensor is the culprit and I don't have to mess with the exhaust yet, I'll probably still replace the up-pipe. I've seen enough horror stories of turbos eating pre-cats that I'd rather spend $150 and not have to worry about it. Link to comment Share on other sites More sharing options...
relative4 Posted April 4, 2018 Share Posted April 4, 2018 The up-pipe is a must for safety regardless of performance goals. The Invidia sucks, a used OEM from any STi is your best bet. Once you have the downpipe, a custom tune is your best bet, but OTS stage 2 is fine. Accessport is easiest, Tactrix and open source is cheaper. Get a catted downpipe, catless is bad news for a bunch of reasons. Midpipe is not a thing. Link to comment Share on other sites More sharing options...
Infosecdad Posted April 4, 2018 Share Posted April 4, 2018 Pretty much all mid-pipes are catless. They might have a resonator (or not), but no cats in them. Link to comment Share on other sites More sharing options...
ZachCouch Posted April 4, 2018 Author Share Posted April 4, 2018 The up-pipe is a must for safety regardless of performance goals. The Invidia sucks, a used OEM from any STi is your best bet. Once you have the downpipe, a custom tune is your best bet, but OTS stage 2 is fine. Accessport is easiest, Tactrix and open source is cheaper. Get a catted downpipe, catless is bad news for a bunch of reasons. Midpipe is not a thing. What's wrong with the Invidia up-pipe? The Cobb catted downpipe for the LGT deletes the midpipe, so that's pretty cool. Link to comment Share on other sites More sharing options...
relative4 Posted April 5, 2018 Share Posted April 5, 2018 Because it's rigid, the Invidia doesn't seal properly unless you reclock the turbo, and likely won't stay sealed then. Plus the (pointless) bung on mine had a bizarre thread pattern that was a pain in the a$$ to plug. Any 2-bolt up-pipe with a flex section is fine, but used STi is best cause it's cheapest, OEM fit, OEM quality, and is least obvious to emissions goons. Link to comment Share on other sites More sharing options...
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