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WRX exhaust


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Ladies and Gentlemen, taking a page out of the NASIOC guide to dealing with a constant stream of noobies, I have decided to put together an exhaust FAQ. This is a living document and I don't claim to know everything, so where we have consensus or documentation, I will make changes appropriately.

The Basics:

The 2015+ WRX and STi have a mostly redesigned exhaust system to go with the new motor and resultant new turbo placement. There are still FOUR main components, although nomenclature gets confusing sometimes. Here they are in order from turbo to tailpipe with colloquial name and official Subaru service manual terminology.

J-pipe - Center Exhaust Pipe (Front) - A short curved pipe that has one catalytic converter in it

I-pipe - Center Exhaust Pipe (Rear) - A short straight pipe with one catalytic converter and one resonator in it.

Mid-pipe - Rear Exhaust Pipe - The long straight pipe that goes from the middle of the car to just behind the axle, splitting to a Y for the mufflers. This piece has a bottle style resonator on the STi version, but is straight pipe on the WRX exhaust.

Axle-back - Muffler (LH/RH) -

A few vendors are selling a single piece to replace the J and I-pipes, which is still referred to as a J-pipe (or downpipe if you're oldschool)

Exhaust Options: There are a ton of options already for these cars and the list keeps growing. I'll try to keep branding out of the picture and speak to the styles of product.

Axleback Muffler/Delete:

A good option for people looking to minimize the risk of a denied warranty claim. These require no tuning to run, and therefore provide very little in the way of horsepower gains.

The full muffler deletes are not very loud with a stock J and midpipe and, at a cruise, are hard to even hear in the cabin. It does sound really nice when you open it up, though. IMO, the 4" muffled version was not really quieter than my delete version.

The main issue with the muffler deletes, or even the muffled axle-backs is that they become pretty worthless when you decide to go "stage 2" and put on a J/I pipe. Taking out 2 cats and a resonator will make the car sound like a racecar. I don't mean that in the cutesy "oh my car goes psh when I shift haha racecar". I mean it will set off alarms and get you pulled over in less than a mile. It trumpets extremely hard and does not really sound good by most people's standards.

If you find yourself in this situation, either because you never read any of the threads or because you're a stubborn idiot, there is a cheap solution. Adding a resonator to the midpipe (or getting an STI pipe with one in it already) will drastically improve the sound and reduce the volume to something reasonable. Yeah you could buy a catback, but when you just dropped $750+ on parts and accessories to go stage 2, an $80 resonator seems a lot more reasonable.

Catback System and Mid-pipe:

There are way too many styles of catback here to be really specific, so I will keep this section shorter. No tune needed so, again, gains are minimal. Your car will sound kind of bad if you don't have a resonated system and add a J/I pipe down the road. Just like everything else in life, you get what you pay for.

You can find straight through !Removed! cans and some larger chamber stock-alike systems that all sound pretty good, but vary on the harshness and loudness spectrum.

There are a few mid-pipes that are able to be installed on their own or with axle-back systems to upgrade your sound.

STI Midpipe - The 2015+ STI has a resonated midpipe that bolts right on to the WRX. This is the second cheapest option for fixing J pipe loudness (~$300 new and somewhat tough to find used). That seems like too much money for a temporarily permanent solution, so I recommend the custom resonator install.

Nameless midpipe - Probably works pretty well to improve sound, with the biggest benefit being that it is a true 3" exhaust piece and can be purchased in a modular fashion with the deletes/downpipe. Unfortunately, the market demand and complexity of the part make it a pretty pricey piece ($600+).

Turboback System and J/I-pipe:

A few of the people that make J/I pipes and cat-back systems sell them in a bundle. You save several dollars.

Unlike the EJ style downpipe, the FA designs are all pretty consistent aside from the cat placement. The Garrett turbo has wastegate flow directed straight into the turbine outlet flow, allowing the entire exhaust flow to go through a round pipe instead of a goofy outlet shape. The change in wastegate design is the result of moving away from old diesel engine turbo technology and really helps to make your choice in J pipe simple.

I'm not sure why people sell the two piece J/I pipes, outside of making it easier for manufacturing. One exception is Killer B, who have crafted a good looking turbo upgrade kit that includes a revised J pipe to accommodate the different turbo flange and position. This would allow one to buy the 2 piece downpipe, and only have to replace one piece when they go big turbo.

There's really only one question to answer for choosing a downpipe, then.

Catted or Catless???

It's up to you. Don't ask us. We don't know.

Just make sure that the converter is closest to the end of the downpipe for optimal exhaust performance. Having it by the turbo makes it light off a little faster, but is not friendly to the really turbulent flow that has just come out of the turbine. Aftermarket cats work well enough to kill the smell when warm, but are not guaranteed to make you pass a sniffer.

The End: I hope this is really helpful for anyone that is new to the 2015+ WRX platform and cuts down on the number of silly posts we see from new members. I plan to add a bunch of video examples and pictures in the next few days, because it's currently just a wall of text.

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