Grimmspeed Catted J-pipe/Downpipe - 2015+ Subaru Impreza WRX 6MT
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.
- 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.
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.
- 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)