Catted J-Pipe/Downpipe - 2015+ Subaru WRX 6MT

SKU: 007103
( 8 Reviews )
3" J-Pipe/Downpipe to OEM Catback Adapter
3-Port Boost Control Solenoid

Current stock: 0

Meticulous engineering meets elegant design.

With the 2015 J-Pipe, the devil is truly in the details and the product development team here at GrimmSpeed has taken the time necessary to knock each of those details out of the park. As a result, what you see here is a meticulously engineered J-Pipe with an innovative flange design, single piece construction, excellent ground clearance and fitment with superb quality and craftsmanship.

Quick Specs

  • Innovative Turbo Flange Design - 1/2" thick while retaining all OEM brackets
  • One-Piece Tube - Ensures exact fitment, robust construction and ease of installation
  • Smooth 3.5" to 3" Transition - Matches turbine outlet size and then reduces quickly to maintain exhaust velocity
  • 100% Made in the USA - Manufactured right here in Minnesota
  • Optimized Tube Routing - Maximize ground clearance and minimize flow restriction without modifying suspension hardware, etc
  • Custom Stainless Turbo Studs - Replace the terrible OEM studs and nuts with these, machined specifically for use with 2015 WRX turbine outlet and our 1/2" flanges
  • Standard 3rd O2 Bung - Allows the future use of aftermarket sensors
  • Grounding Strap Mount - Retains all factory functionality
  • 300 Cell Metallic Substrate Catalytic Convertor (Catted Models Only) - Excellent balance of the reduced restriction of a 'race cat' without the stink of a 200 cell unit

Performance and Tuning

Performance of the J-Pipe was verified on our 2015 WRX using the following method. Our tuned baseline run is the same run that we used in showing the boost control performance of the GrimmSpeed 3-Port Solenoid. We then installed the J-Pipe and retuned the car, using the exact same tuning methodology to ensure consistency. This ensured a real apples-to-apples comparison between the stock J-Pipe and the GrimmSpeed unit. The results showed a gain of 26.7whp (14.1%) and 19.8wtq (9.0%) and are displayed in the chart to the left. The percentage gains should be the focus here, as this particular dyno reads very low (stock baseline was 171). From a completely stock vehicle, users can expect a gain of around 45whp (27%) and 70wtq (41%) with the installation of the GrimmSpeed J-Pipe and custom tuning. The chart on the right shows this comparison.

grimmspeed j-pipe 2015 wrx   grimmspeed 2015 wrx j-pipe dyno


Our engineers began by 3D scanning the OEM J-Pipe and vehicle underbody using our in-house FARO Arm. That data was used in CAD to design a pipe that fits perfectly within the tight underbody packaging on a 2015 WRX without sacrificing ground clearance. The 2015 WRX uses a series of OEM brackets to support the weight of the turbo and J-pipe, the most important of which bolts to the turbine outlet flange. Our engineers insisted on using thick 1/2" stainless steel flanges, but also knew that without a clever design, the very important OEM brackets would no longer line up. The GrimmSpeed flange design uses a CNC machined pocket that the OEM bracket sits in during installation, allowing the use of 1/2" thick flanges as well as the factory turbo support bracket!

Finally, they worked tirelessly to design and manufacture a J-Pipe that could be bent from a single piece of tubing. This allows for more efficient manufacturing, less potential failure points and a product that fits perfectly each and every time.


In true GrimmSpeed fashion, no corners were cut in the fabrication of each and every one of these J-Pipes. A proper design is no good without proper material selection. In this case, 304 series stainless steel is the best choice for durability, corrosion resistance and cost efficiency. Flanges are machined from 1/2" thick plate and the primary tube is CNC bent, laser cut and expanded from 3" tubing. O2 bungs (three of them) and our custom turbo studs (included) are both machined on a CNC lathe from 304 rod. Finally, finished assemblies are TIG welded using 308L filler rod.


Last, but certainly not least, is construction. A solid design and robust materials are nothing without use of the correct manufacturing methods and welding processes. Each GrimmSpeed J-Pipe is welded in the same master weld fixture. When not in use, a 'master pipe' lives in that fixture, allowing for a quick check, before each production run, that the fixture is still accurate. Even that isn't good enough for our engineers, so they 3D scan the fixture and master periodically, to ensure accuracy.

Includes everything

  • 1x Welded J-Pipe Assembly
  • 1x GrimmSpeed Stainless MLS Turbo to J-Pipe Gasket
  • 1x GrimmSpeed Stainless MLS J-Pipe to Catback Gasket
  • 4x Stainless turbo studs w/ nuts
  • 2x Replacement catback bolts w/ nuts
  • 1x O2 Sensor Plug (plugs third O2 bung for future use)
  • 1x Grounding Strap Bolt (not pictured)
  • 2x GrimmSpeed License Plate Frames
  • 1x GrimmSpeed Sticker


  • 2015+ Subaru WRX (Manual Transmission Only at this time)

Install Guide

COMING SOON - Written - 2015 Subaru WRX J-Pipe/Downpipe Installation GuidePDF Document Icon


8 Reviews

Jorden 1st May 2019

love it

Well crafted and good fitting part, removing the stock cat/front-pipe was a huge pain due to one of the brackets being hard to remove and being unable to clear the studs with it on (it contacts the water pump before you clear the stud) ultimately I had to remove the stock catalytic converters heat shield to wiggle the bracket out of place so I could get the cat to clear the stud without contacting the water pump, once the old one is off the install is super simple because the cat is at the back of the GS j-pipe so there's a lot more room for tools on the install portion, I would highly recommend doing this job on a lift as it would be a huge pain to try and do it on jack stands, looks and sounds awesome

Andrew 7th Mar 2019

Grimmspeed Catted Jpipe on 2018 WRX

Install: I opted to do this myself, and initially was planning on just putting it up on jacks and stands, luckily I had access to a lift and just went for it. I could not imagine doing this install without a lift. For the 2018+ wrx I noticed that one of the turbo mount brackets actually needed to be accessed with a long socket wrench from top down into the engine bay of the car, and was inaccessible from the bottom, small issue, but took a second to figure out. The turbo studs are unrealistic to reach without removing the stock jpipe heatshield, which will need to be bent and manipulated off. For the actual install, the only two difficult parts are the upper right turbo stud, which does require a painfully specific long, yet slim socket with swivel joint and plenty of PB blast beforehand, and the second pain being realigning the turbo bracket after mounting the pipe. It's a tight fit, and can take some manipulation as well to avoid cross threading. This being said, this has nothing to do with the quality of the product itself, and is no fault of Grimmspeed, we can blame Subaru for the inconvenient access here. Product: the pipe itself was hefty and satisfying. Great welds, solid single piece construction, included hardware was free from imperfections and high quality. No fitment issues. Due to nameless having a unique bellmouth midpipe, I ended up squashing a 3 inch donut gasket to the Grimmspeed jpipe and tightened it down with the Grimmspeed hardware. No issues, no leaks. First drive: After flashing the OTS stage 2 map (go ahead flame me, poor with no protune) and starting it up for the first time, the sound difference was night and day, super aggressive, slightly raspy, and the turbo whistle was finally audible and ever-present. After letting the engine warm up from a cold start it actually went down to a nice quiet idle and was not obnoxious whatsoever (I am running a resonated nameless catback with 4 inch mufflers to give you an idea). The power delivery and response was awesome, the turbo whistle again really changed the way the car sounded. Beautiful 3rd to 4th pops under load, and an awesome subtle series of crackles and pops on a rev match and downshift. Felt like driving a completely different car and made me fall in love with it all over again. I've gotten tons of compliments on the exhaust note since showing it off to friends. Kicking myself for not buying this earlier. Have driven around 1000 miles since install so hard to tell if there are going to be any issues, but none so far after running some logs. All being said, despite the painful install, was satisfying to work on the car myself, and very satisfied with the sound and slight power gains with the stage 2 map. Would definitely recommend this to those on the fence, how can you beat high quality American stainless steel? Cheers, and thanks again to Art for taking care of me on the phone to answer my questions before purchase.

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