For the 2015+ Subaru WRX, an aftermarket downpipe (otherwise known as a j-pipe) is one of the most substantial horsepower adding modifications you can do. With so many on the market, it can be hard to know which one to choose. We've compiled a list of the best, whether you want to go catless or catted, sticking with a high flow catalytic converter. We've compared them to help you make your decision easier. A downpipe is required for a stage 2 tune and will really bring your car to life.
Tuners are reporting gains of up to 55 hp with 93-94 octane fuel with an aftermarket j-pipe. This depends heavily on the octane rating of the fuel used. With California 91 octane fuel, you may see gains of up to 40hp with an e-tune. Cobb reports gains of up to 62 whp. The power gained from installing a downpipe can vary depending on your specific car, variances in dyno measurements, and other factors, but any way you look at it, this is one of the biggest single power adders.
Tomioka Racing has been around since 2006, bringing the car enthusiast community high quality performance modifications. Tomioka's products are all of the best quality and fitment. Their staff works tirelessly to put out great products and offer great customer support.
This high-flow catted downpipe from Tomioka Racing is made from quality polished Stainless Steel 304, and the weld quality is fantastic. Its 3" mandrel bent tubing and high-flow catalytic converter frees up a ton of restriction from the exhaust, making room for an experienced tuner to work their magic. The placement of the catalytic converter near the turbo reduces the chance of boost creep. It comes with an adapter flange for use with the stock catback, or can be used with most aftermarket catback systems.
Tomioka Racing also offers a catless version of their j-pipe for the Subaru WRX, for those who'd prefer it. Just like the catted version, this downpipe is made from Stainless Steel 304 and the quality is all around fantastic.
The catless downpipe comes with adapter flange for use with the stock catback system. If you're planning to go catless, know that while there's some extra power gains, you'll likely need to use an external wastegate. This is an excellent catless j-pipe that we can highly recommend.
Mishimoto is another popular name in the Subaru tuning community, offering upgraded parts such as exhaust, intakes, intercoolers, and radiators. If you're looking to go catless, Mishimoto's j-pipe is a great choice. This downpipe fits both the manual and CVT versions of the Subaru WRX.
The Mishimoto catted downpipe includes a second O2 bung for adding a wideband O2 sensor and a place to connect the stock grounding strap. It includes replacement gaskets and all the hardware required for the install.
In addition to their catted downpipe, Mishimoto also offers a catless downpipe for those who prefer it. A catless j-pipe frees up some restriction in the exhaust, even when compared to a high-flow catalytic converter. This allows for more potential power gains with the proper tuning and supporting mods.
One drawback to catless downpipes is you'll usually need an external wastegate to prevent boost creep. If you're aware of the drawbacks and are willing to invest into the extra power gains, then the Misimoto catless downpipe is a good choice for the Subaru WRX. It includes all of the required hardware for installation.
Grimspeed offers a catted downpipe for the 2015+ WRX in a one piece design. They designed this downpipe by scanning the OEM J-Pipe and using CAD to create a downpipe that fits tightly under the body for the 2015+ WRX without losing any ground clearance. The design allows for using the OEM mounting brackets. The single piece design gives fewer potential points of failure.
The Grimspeed downpipe includes gaskets, 4 replacement turbo studs which commonly strip during installation, 2 replacement catback bolts, a plug for the 3rd O2 bung, and bolt for the grounding strap.
MAPerformance is known for their performance parts for Subaru, Mitsubishi, Nissan, BMW, and more. They started in 2006 and have developed a reputation for making turbocharged vehicles fast and powerful.
MAPerformance's j-pipe for the WRX is an excellent choice along with their off the shelf tune. It's made from 100% stainless steel in the United States. The stock downpipe is a huge bottleneck in the exhaust flow, and MAPerfomance's aftermarket downpipe will free that up and add serious power.
Cobb is a very well known name in the Subaru tuning community, with their AccessPort, a staple in every tuner's arsenal. Included with the AccessPort is a Stage 2 tune designed to work with this downpipe, so you can install it, and flash the preloaded tune and be up and running quickly and easily.
This downpipe is a popular choice since it includes a resonator. With the factory downpipe removed, many WRX owners complain about a "drone" while cruising, and a resonator helps to eliminate that, while still letting the engine scream when you push it. It's made from 3" piping and includes an adapter to connect to the factory catback system.
Invidia is well known for their exhaust parts for Subaru, but also other brands such as Acura, Ford, Honda, Mitsubishi, Infiniti, and more. They offer high quality parts, manufactured in Los Angeles, California.
Their exhaust systems for the Subaru WRX are very popular, and their catless j-pipe is an excellent choice. The catalytic converter is located next to the turbo so that it will heat up and start working faster, as well as make boost creep less likely. Invidia's catted downpipe is one of the best choices for the WRX.
If you want to go catless, Invidia's catless downpipe for the 2015 WRX is a great option. Many people choose to go with a catless downpipe to free up as much restriction in the exhaust as possible.
Catless downpipes don't come without their drawbacks. For one, it may be difficult to pass a visual smog inspection, and some WRX owners report problems with boost creep, and have installed an aftermarket boost controller and external wastegate to mitigate this. If you're aware of these issues and think the gains are worth it, then catless downpipes can be a good choice.
Invidia's J-Pipe is an excellent choice. It includes 3 O2 bungs, two for the stock oxygen sensors, and another so you can install an aftermarket wideband sensor.
Yes, an aftermarket downpipe will make the car louder. Both downpipes high-flow catalytic converters and catless downpipes remove the largest restriction from the exhaust system. In addition to this, most aftermarket downpipes don't have a resonator like the stock one does
Yes, a tune is absolutely required. You can either flash an off-the-shelf tune with a Cobb AccessPort, or for best results, have a custom tune made, either an e-tune or in a dyno tuning shop.
Tuners have seen gains of 55 whp or more on 93-94 octane fuel. Gains of around 40 whp may be more common on 91 octane fuel.
While catless downpipes free up more restriction in the exhaust system and allow for more potential power gains, they have some drawbacks. You'll likely need to install an external wastegate as well, since with the increased flow, exhaust gasses end up bypassing the internal wastegate and causing boost creep. Additionally, catless downpipes can't legally be used on the road anywhere in the US.