2015 WRX stock exhaust system

Make your presence known. The Mishimoto 2015 WRX Cat-Back Exhaust! Part 1: Initial Fabrication

Interested in purchasing our 2015 WRX cat-back exhaust? Check out more details on our product page linked below!

Subaru WRX/STi Cat-Back Exhaust

An aftermarket exhaust is an easy way to distinguish your car from the slew of vehicles roaming the streets. Not only does it enhance aesthetics, but the amplified noise is also a dead giveaway that you are an automotive enthusiast. For many of us, an exhaust is a simple initial upgrade that will enhance the driving experience and provide greater enjoyment. With a variety of options popping up, it can be difficult to select a setup that will provide the noise level and tone that you want from your Subaru.

We are no stranger to exhaust components. Many of you kept up with the progress of our build for the FA20 downpipe we developed and released a few months ago. Thanks to a skilled engineering team, high-quality materials, attention to detail, and impressive craftsmanship, we were able to deliver exactly the product that our customers needed.

This brings us to the cat-back. We spent a great deal of time researching exhaust systems for the 2015 model WRX as well as the previous generation. We noted any downsides with other products, and we read comments and feedback throughout the forum, which helped lead our team in the right direction for our design. Additionally, we polled the forum regarding a few design components we were considering. (See tip selection below.)

http://forums.nasioc.com/forums/showthread.php?t=2667896

WRX Factory Exhaust

So what do you get from the factory on your new WRX?

2015 WRX stock exhaust system
2015 WRX stock exhaust system

The stock system begins as a single, 2 3/8” pipe, extending from the downpipe back to the rear axle section. Once past the differential, the exhaust splits to a Y, with two 1 7/8” pipes feeding large mufflers. The mufflers are a single-in, dual-out design with a total of four tips. You will notice that the midpipe resonator present on the previous generation is no longer used on the WRX.

STI Optional Factory Exhaust

The STI/SPT exhaust system is a stock option for the 2015 WRX, and our 6-speed vehicle was equipped with this particular system. Check it out!

2015 WRX STI edition exhaust system
2015 WRX STI edition exhaust system

This system starts with 2 1/2” piping leading to a similar Y junction around the differential. Once split, the piping size drops to 2” before entering a dual-muffler system. On this setup, each muffler features a dual inlet and dual outlet.

Stock Exhaust Comparison

The STI system shown above is noticeably louder than the stock cat-back system, although still reasonably quiet. This is likely attributed to the larger piping and higher-flow mufflers. The mufflers on the stock system are massive, which is why the WRX is a quiet vehicle from the factory. Neither stock system causes highway drone, and both are certainly acceptable for daily driving. That said, we are still seeking a more aggressive tone.

Fabrication Begins

WRX fabrication and testing
WRX fabrication and testing

We decided on a few basic design constraints and began fabricating the front section of our cat-back prototype. Check out a few shots of the early progress. First, the front flange was installed and the initial pipe tacked into place.

Flange tacked into place
Flange tacked into place

Next we ran a length of pipe toward the rear axle.

Midpipe mockup
Midpipe mockup

We then routed the rear portion of this pipe toward the driver side, following a path similar to that of the stock piping.

Midpipe mockup
Midpipe mockup

So, up to this point, how does our piping differ from the stock unit? So far, our cat-back unit is constructed from 3” stainless steel. This larger diameter will have an impact on the noise level and tone of the exhaust, not to mention the improvements in flow.

Next, we fired up the torch to bend some hangers into shape. Everyone loves playing with fire and metal!

Bending the exhaust hanger
Bending the exhaust hanger
Bending the exhaust hanger
Bending the exhaust hanger

Our next task was to construct the rear portion of the cat-back system, which includes the mufflers. We had an idea for testing numerous muffler designs to determine which one provided the highest-quality tone, without producing the dreaded highway drone associated with most aftermarket exhaust systems.

Additionally, we would be evaluating power output increases resulting from  the improvement in flow from our system. Our previous tests have shown that a larger cat-back system can provide increases in power, even on the stock tune. We shall see!

Interested in purchasing our 2015 WRX cat-back exhaust? Check out more details on our product page linked below!

Subaru WRX/STi Cat-Back Exhaust

 

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