Make Some Noise: Optimizing Your Turbo with a Cat-Back Exhaust and Cold Air Intake

The one single modification to this WRX is the addition of the WRX STi factory catback, which is easily identified by its large, single outlet. The stock WRX unit features two smaller outlets. While the STi catback offers a slightly deeper tone at idle than the WRX, it pales in comparison to aftermarket systems such as the Magnaflow catback we’ll be installing. Soak all of the fasteners as well as the rubber hangers with penetrating oil.

Now you can begin to remove the fasteners that hold the catback to the downpipe. Keep track of all of the factory washers and springs.

You’ll be reusing all of the factory hangers, so inspect them for wear and tear and replace as appropriate.

In this photo, you’re looking up under the downpipe at the back of the turbo. The fasteners holding the downpipe to the turbo can prove problematic from rust and from the intense heat and heat cycling. Take your time and expect a bit of difficulty here. Some of them are easily reached from the engine compartment as well.

Once you’ve wrestled the downpipe free from the turbo, you can extract it from the car. One of these catalytic converters is likely the cause of our low-efficiency engine code, but we’ll be replacing it with a higher-flowing new replacement.

As we mentioned earlier in the main text, some of the fasteners fought us. Luckily none of them broke off in the turbo housing.

Here we can compare the new Injen catted downpipe to the stock one. Injen’s Super SES downpipes are CNC mandrel-bent, and made from 100 percent 304 stainless steel.

The new Magnaflow piece’s stainless steel construction should provide long-lasting good looks versus the factory setup, and the mandrel bends provide better airflow. The muffler is a straight-through design for improved flow and a louder exhaust note. The Magnaflow catback will bolt up to stock downpipes as well, should you not be ready to make that change yet.

We recently replaced the metal turbo gasket on our subject vehicle and felt it was in good enough shape to reuse. You may want to order a new one if yours is still original.

After connecting the downpipe to the turbo, we found that the lower mounting bracket didn’t quite line up with the one on the car. We muscled it into place, and will check to see if perhaps we have a broken or failing engine mount that is creating the issue.

Another issue that we encountered was the drain tube coming in contact with the larger downpipe. This was easily resolved by removing the hose from the factory frame clip, turning it sideways and propping it up in the frame rail for the time being. A more permanent solution would be to remove the factor clip, create another hole in the frame rail and replace it out of the way.

The Magnaflow catback fit perfectly underneath our WRX. Make sure you have a friend keep an eye on the muffler and tail pipe tip to make sure it is straight before you tighten all of the fasteners up. The Hangers do a good job of keeping it in the proper position though.

K&N Engineering’s Typhoon series cold air kit that we picked out (Part Number 69-8001TS) is 50-state legal and the filter element can go 100,000 miles without maintenance (depending on use). This kit is available in a number of finishes—we opted to go with the silver powdercoat.

Our WRX has had the front air ducting removed, as well as the snorkelsaurus ducting in the fender, as it is often referred to on the Internet.

To get started on the K&N install (after disconnecting the battery if you haven’t done that already), we need to disconnect the mass air meter. The meter will be relocated to the new K&N charge pipe.

Next up are these coolant lines, which need to be freed from their stock clips. You’ll be moving these around for the time being, but there is a provision later on to secure them.

To remove the top of the air filter box, loosen the worm clamp, disengage the clamps around the perimeter of the lid and then pull it out.

Remove the flexible intake ducting from the turbo inlet tube next by loosening the worm clamp.

The bottom of the air box unbolts from the fender and the frame rail. Then you can remove it from the vehicle.

23. It’s time to swap the mass air meter over to the K&N charge pipe. The stock fasteners use a Torx bit, which can be a bit stubborn if they’ve never been loosened before. Do you best not to strip them. K&N supplies new fasteners to mount it to the charge pipe.

You need to temporarily remove this bracket so you can reroute the mass air meter harness per the instructions.

Unclip the mass air harness from the bracket and then remount the bracket. The top bolt that goes to the fender will also bolt up the K&N heat shield, so you can leave that out for now.

Install the included silicone coupling onto the stock under intake tube. The factory coupling that connects the turbo inlet tube to the turbo inlet can become brittle over time, so be careful when installing the K&N coupling.

Assemble the charge pipe to the black heat shield panel. The bolts go through the charge pipe flange and screw into the included venturi cone that goes on the other side.

Don’t forget to mount the included heat shield to the charge tube when bolting it to the black panel.

K&N includes a couple of weather strips in the kit. The thicker of the two runs along the top side of the black heat shield and seals it to the hood.

An extra pair of hands comes in handy when setting the K&N Typhoon intake into place. The coolant lines being held out of the way will fall into the U channel, and you simply remove one of the stock plastic coolant line clamps from the factory air tube and insert it into the K&N panel to secure them. Then use the original lower airbox fasteners to secure the K&N panel to the frame rail and inner fender.

With the Typhoon in place, you can definitely hear the rush of air going into the engine now, and the more open design will support future upgrades in boost or performance parts like a bigger turbo! While we didn’t have the opportunity to perform a before and after dyno comparison, K&N claims to have seen up to a 15hp increase in this application. Truthfully, we’re in it to hear the cool sounds!