From Stock WRX to Daily-Driver Track Terror – Part Three
By: Chris Neprasch
First off, catalytic converters help keep the environment clean. You’ll get in big trouble with the authorities in some states if you ever get caught on the street without them and they help lower emissions so much that Subaru put three of them on the WRX so it would be allowed into the country. Now that being said, after installing the Injen catless exhaust, catless down pipe and catless up pipe, the catalytic converter count on the WRX we are building to kick some arse at the track has now gone from three to zero. And the Injen items strictly for off-road use have given the Subaru a swift smack bottom to the pants.
If you caught last week’s article on how to install an Injen intake and front-mount intercooler you would know that we put half of their complete WRX package onto our Sube. With the turbo seeing cooler air and the front-mount cooling it off even further, it’s time to direct our attention on how to make the exhaust more efficient. To do this we are going to install an up pipe, down pipe, cross pipe and exhaust to the WRX thus increasing flow allowing exhaust gases to flow more freely in and out of the turbocharger.
Cross Pipe Install
The 2.0-liter is horizontally opposed or as it is also referred to, a Boxer engine. Each side of the engine has its own exhaust manifold and a cross pipe connects the two before they enter the up pipe. To remove this you must first take the heat shields off each manifold. Each side is slightly different and the heat shield on the driver’s side will come off once the bolts are removed.
The passenger side is a little tougher to get out. Between the chassis and the upper part of the exhaust manifold is a sensor that either must be removed or unplugged and then have the wire fed through the access hole while you’re pulling the heat shield down. We decided to go with the unplugging route and followed the wire up to the engine bay until we found a point were it could be detached.
With the heat shield out of the way, we sprayed the four nuts and bolts – two of each on each side where the cross pipe meets the cast iron exhaust manifold – with WD-40 and let is soak for a couple of minutes. The four bolts came out easily and the cross pipe was removed. We removed the heat shield on the factory cross pipe to examine the difference between the two. Injen’s has a slightly larger diameter pipe with fewer, smoother bends.
Place the Injen cross pipe between the two sides of the exhaust manifolds, reuse the factory gaskets and hardware, torque them down and you’re done with that the install.
Down Pipe and Up Pipe Install
To install the up pipe, the down pipe must first be removed. Since we had both the new Injen up pipe and down pipe, we did both at the same time.
The first two things in the down pipe removal process are either unplugging or removing the oxygen sensor and then unbolting the lower, rear part of the down pipe from the exhaust. This will keep you from running into any surprises later when you’re trying to drop the down pipe.
To gain access to the bolts holding the down pipe to the turbo, you must first remove the heat shield. Notice the hands off warning – please remember to let the engine cool completely down before you go wrenching on parting that see gases in the plus-1,000 degree range. The heat shield has two nuts bolts holding it to a bracket and the others are around the turbo. Take off of them off and pull the heat shield out. If it doesn’t want to come out then you probably missed a bolt or two, but search around because they are all visible when looking down at it.
Remove the hardware holding the down pipe to the turbo and the down pipe can be pulled out from the bottom. Once again feel and look around to make sure you got all of the bolts before you go yanking on the down pipe too hard. Once they are all taken off it should only take a light tug to get it free.
The up pipe removal is more complicated than taking off the down pipe. Once again there will be a sensor that needs to be unplugged. A pair of nuts and bolts holds the up pipe to the exhaust manifold on the bottom of the engine. They are easily removed with some help from our friend WD-40 and then it’s time to go back up to the top of the engine. Five nuts thread on to studs that hold the up pipe to the turbo. There were no problems pulling ours out – the problems started when the up pipe was completely unbolted. It didn’t want to come out through the bottom or top of the engine so we had to jack the engine up to gain enough clearance to remove it. We undid the bolts on a bracket holding the tranny to the body, took the two passenger side lower motor mount nuts out and put a jack underneath the engine. It only took about two to three inches of raising the engine to get the up pipe out, but we still had to do it. Before you drop the engine back down, put the studs that Injen provides with their up pipe on it, put the sensor from the factory up pipe in it and slide it into position. Reuse all of the factory hardware and put the Injen up pipe and down pipe just like how you took the factory ones out. (We don’t usually like to say reinstall in reverse of removal, but in this instance it’s so straightforward we did – OVB)
The folic looking protrusion from the rear of the down pipe is where the oxygen sensor goes. It might look a bit odd, but it was designed this way to keep the dreaded Check Engine Light from flashing regularly.
The factory exhaust system is divided into two sections after the down pipe. The first part has a catalytic converter and runs back right to a break right before the axle and the second section has the muffler. Assuming the front of the exhaust system is already disconnected from the down pipe removal then undo the two sections from each other.
Three hangers hold the rear section in place. The rubber hangers can be pulled off of the mounting brackets and the section will just drop. In the middle of the section with the catalytic converter there is only one hanger – take it off and remove the piping.
A side-by-side comparison between the two and it’s obvious why the Injen exhaust flows better. Not only is the piping physically larger, it also doesn’t have the drastic turns and the turns themselves are mandrel bent for less air restriction.
Start by putting the rear section in first mainly because it has three hangers to hold it in place versus only one. Take the stock hangers and slide them on to the new brackets then put it in place using the three factory mounting points.
New nuts and bolts come with the Injen kit along with a new gasket. Use them where the center pipe meets the rear pipe after putting the center section on the hanger, but only make them snug. Go back to where the exhaust meets the down pipe and torque those two bolts down. Before completely tightening the rear exhaust connection, make sure there are no clearance issues and everything is aligned properly then you’re done.
Now both the intake and exhaust are taken care of. But it takes more than power to be successful on the track or at an autocross event. Most of the performance comes in and out of the turns so if we don’t like getting passed regularly then that would be next on the agenda.
285 Pioneer Place
Pomona, CA 91768