Driving 5

Make your presence known. The Mishimoto 2015 WRX Cat-Back Exhaust! Part 2: Finalizing the Prototype

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

Prototype Fabrication

With the front section of our exhaust complete, we needed to address the Y-section as well as the pipes routing to the mufflers. We decided to go with 2 1/4” piping following the Y-section, which matches the diameter of the STi system.

Check out a couple shots from the fabrication process.

Fabricated muffler section
Fabricated muffler section

We bent a few more hangers for attaching the mufflers to the appropriate stock locations.

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

Once our design was completely tacked up and fitment was verified, we began the complete welding of our cat-back. We back-purged the piping to prevent “sugaring” of the internal portions of the weld. Yes, it is just a prototype unit, but we are planning to use this unit for sound testing to determine our muffler choice.

Welding the prototype exhaust
Welding the prototype exhaust
Welding the prototype exhaust
Welding the prototype exhaust

Once this unit was completely welded, we had a functional prototype for testing. Check it out!

Prototype Reveal

Cat-back prototype for testing
Cat-back prototype for testing
Cat-back prototype for testing
Cat-back prototype for testing

So, what do we have here? Our cat-back features a 3” pipe diameter from the downpipe flange back to the Y-section. Following the Y-section, our pipes are 2 1/4” in diameter. Instead of a bolted flange, as is used on the stock exhaust, we incorporated V-bands into our prototype, which will allow for quick changes of the rear exhaust portion. As we mentioned earlier, we wanted to test a few different muffler designs to see the effect on tone, volume, and drone. The V-band setup would allow us to swap the muffler sections a bit quicker.

You will also notice some shiny tips on this system. These are not off-the-shelf generic tips. Our team designed these from the ground up using the recommendations we received from you guys on the forum.

Development of the Exhaust Tips

Tip design started with the 3D modeling process. Our team designed the tip in Solidworks and 3D printed a useable prototype to ensure it fit properly and was aesthetically pleasing.

3D-printed exhaust tip prototype
3D-printed exhaust tip prototype
3D-printed exhaust tip prototype
3D-printed exhaust tip prototype

We threw a quick coat of paint on the tips and installed them on the vehicle to see how they looked with the bumper.

Exhaust tip mockup
Exhaust tip mockup
Exhaust tip mockup
Exhaust tip mockup
Exhaust tip mockup
Exhaust tip mockup
Exhaust tip mockup
Exhaust tip mockup

Once we had our tips positioned in the proper location for the aesthetics we were seeking, we made the necessary changes to our 3D design. We then developed a working stainless steel prototype to attach to our existing exhaust system. Check out a few shots of the plastic unit to our finished product.

3D prototype tip (front) and functional prototype (rear)
3D prototype tip (front) and functional prototype (rear)
3D prototype tip (left) and functional prototype (right)
3D prototype tip (left) and functional prototype (right)

Our final design is shown in the Solidworks rendering below.

Exhaust tip rendering
Exhaust tip rendering

Now, we had to address the mufflers.

Mufflers

The rear portion of our exhaust system is secured using V-band clamps. As explained earlier, this setup will make muffler swaps quicker and easier for testing. We will be testing a few different muffler designs to determine which one sounds best and performs to our standards. The round single inlet/outlet muffler you see below is one of our options.

Experimental muffler
Experimental muffler

Take a look at the massive stock muffler! My guess is that our system will also cut a few pounds off the weight of the WRX.

Stock 2015 WRX muffler
Stock 2015 WRX muffler

Check back with us next time for some audio of our initial road and dyno testing!

Driving 5

Thanks

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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