From Stock WRX to Daily-Driven Track Terror – Part Two

By: Chris Neprasch

It’s no secret that the cold air makes more horsepower than hot air. In turbocharged cars this creates a problem since the turbo itself is powered by exhaust gases exiting the combustion chamber. Explosions don’t create cool gasses so the more you can do to bring temperatures of the compressed air down before they enter the engine the more horsepower and torque will be made.

Some would argue that an aftermarket cold-air intake doesn’t do much on a turbocharged vehicle since the air is going to be heated up by the turbo anyway. Unless you live in a world free from the laws of thermodynamics, installing cold-air intake will reduce air temps going into the turbo as well as coming out. To simplify it, if you put a room temperature piece of bread in the toaster for a full cycle it would pop out browned and warm. Now if you took a frozen piece of bread and put it in the same toaster for the same amount of time, it’s going to take more heat applied for a longer duration to get the same result. Replace the bread with air and the microwave with the turbocharger and you get the basic theory.

The air exiting the turbo on its way into the engine still does get heated up substantially, but it can be further cooled by adding an intercooler. They come in different sizes and shapes. Air-to-air intercoolers are the most widely used style in the sport compact world and does exactly what the name implies; they use air to cool the air entering the engine. Liquid-to-air intercoolers use liquids like water to cool the air going entering the engine.

Rather than mix and match different parts we decided to use Injen Technology’s new package for the WRX on our Subaru. The package consists of a cold-air-intake to held aid in the cold bread in the toaster scenario, front-mount intercooler to get air temperatures even lower along with other parts like up pipe, down pipe, exhaust and front crossover pipe. This article will focus on the induction side of the package with the installation of the cold-air intake and front-mount intercooler.

Cold-Air Intake Install
Being the typical lazy asses we are, of course we started with the easier task of installing the Injen intake. Removal of the front bumper isn’t required, but it is extremely helpful to keep the install moving along smoothly. Plus it had to come off for the front-mount install anyway. The first order of business was to remove the bottom skid plate. Five bolts and several clips hold the plate on. All of the clips are in plain sight and can be easily taken out by using a screwdriver to lift the middle section and then pulling on the outside.

Get used to working with these clips because there are more of them holding on the front bumper. Four are hidden behind the fog light covers. The fog light covers have two notched that a screwdriver can be carefully placed in to pop them out. There are more clips near the top of the headlights and inside the fender wells (There is also a screw on each side hiding way up toward the top). Three different style clips holding the grille on that also need to be removed. If the bumper doesn’t pull off with a moderate tug then double check to make sure you didn’t miss anything.

Unplug the sensor on the stock air box as well as loosen the nearby hoses from their bracket. Unscrew the hose clamp until it is large enough to allow the intake house to be pulled off of the throttle body. Open the air box to make the bolts mounting it to the body accessible. When they have been removed then the whole box assembly can be pulled from the car.

Once the front bumper and air box are off, the resonator can be removed from the passenger side of the car. The box is held on in three different locations. One is on top of the box toward the front of the car, the second is a bolt toward the rear of the car and the third is a nut that can be accessed from underneath the hood. As soon as all three are removed the box pulls right out.

Included with the Injen cold-air intake kit is a 12-inch vinyl trim that goes in the opening where the resonator box came through the fender. The trim protects the polished aluminum from rubbing the fender.

Factory ground location.
New grounding point.
The ground wire near where the resonator box was needs to be relocated. There is a bolt toward the front of the car that serves as the new ground spot. The wire is long enough to reach and to make sure to maintain a proper ground, take a screwdriver or wire brush and scrape off some of the paint underneath the bolt.

The reason for the relocation of the ground strap is to make room for a vibra-mount that Injen includes with the kit. It screws right into where the ground cable was and offers a solid but flexible mounting point for the new intake.

Slide the 2 7/8 inch straight hose over the throttle body and then put two hose clamps very loosely around the hose. Being careful not to scratch it in the process carefully put the intake tube into place. The tube has to be put through the hole in the fender first and then can be moved around until the bracket lines up with the vibra-mount and it can be placed inside of the straight hose on the throttle body. Once everything is lined up then tighten down the hose clamps and the nut on the fender bracket. Put the air temperature sensor into the flange. Make sure the post and cutout on the sensor are lined up then tighten it down and plug it in. Install the cone filter at the other end of the intake using the last hose clamp to secure it and you’re done with that.

Front-Mount Intercooler Install
The factory Subaru intercooler sits on top of the engine and gets air blown through it via the functional hood scoop. Temperatures under the hood are higher than outside of the car and everyone knows that heat rises. Subaru’s top-mount intercooler is air-to-air so warm air doesn’t drop temperatures as quickly as cold air does. Injen’s kit moves the intercooler from on top of the engine to a cooler environment outside of the car where it can be more effective. The intercooler can flow up to 400 horsepower, doesn’t require cutting the bumper support and still retains the factory fog lights.

Removing the top-mount intercooler is the first step since the bumper was already still off. Vacuum hoses have to be disconnected both ends of the hard vacuum line that runs on the front of the intercooler as well as on the blowoff valve. Loosen two bolts on the passenger side, two on the driver’s side and the two near the back of the intercooler by the firewall on the underside. There is a big hose on the front and on the underside that need to be loosened and the intercooler will pull out.

Included in the front-mount intercooler kit are 22 inches of 12 mm heater hose and a T fitting. The T fitting goes on the passenger side where the two hoses were disconnected from the Subaru intercooler and the long piece of 12 mm hose runs across the engine bay like the hard line did and attaches at the same spot on the driver’s side.

Remove the blowoff valve from the intercooler and install it on the flange on the new piping. Put a 2 inch straight hose on the side opposite of the way the blowoff valve is facing, slide on a couple of hose clamps onto it and then put it in the engine compartment with one side of the straight hose over the new pipe and the other over the turbo inlet port. Screw the hose clamps down far enough so that the pipe is being held in place, but snug enough so there is still some play then connect the vacuum hoses going to the blowoff valve.

Before the section of piping that connects to the pipe that was just installed and runs down to the intercooler can be put into the car, the factory radiator catch can needs to be replaced with the hew one supplied by Injen. Be aware that even though you are supposed to reuse the factory plastic overflow cap on the Injen overflow can, ours did not fit anywhere near snug. Now you can lower the pipe into position then connect it to the pipe with the blowoff valve using 2 1/4 inch straight hose. Reuse the stock bolts and thread them loosely into the driver’s side factory intercooler bracket.

Put the 2 3/4 inch straight hose over the throttle body port with two hose clamps loosely slid over and install the passenger side intercooler piping. There is a bracket on the top piece that reuses the factory bolts and mounting tab. A 2 1/4 inch piece of straight hose and a couple hose clamps go onto the connection between the top section of the passenger pipe and the lower. Make sure all of the straight hose connections done thus far have a hose clamp for each side of the connection and are snuggly tightened.

Now comes mounting the intercooler. Like we said earlier, unlike most front-mounts, the Injen unit doesn’t require any cutting of the factory support beam. Just take out two bolts on the underside of the frame, line up the intercooler with the holes and screw the bolts back in.

Attach the C sections of piping on each side with 2 1/4 inch straight pipe then adjust all of the pipes until everything fits properly. Go through the two top brackets and all the pipe connections and torque everything down.

Here’s the fun part. While no cutting is required on the actual bumper support beam, the bumper itself requires a decent amount of cutting which is to be expected with any front-mount intercooler. Injen includes where to measure and how much to cut at each point in their instructions.

What wasn’t included in the instructions was the cutting required on the skid place as well as on the inner fender lining. Once all of the cuts were made the bumper popped right on and true to their claim, we were able to keep the factory fog lights.

Though all components of the Injen piping package are sold separately, they all work together to increase efficiency and breathing. Now that the intake side of things is completed it’s time to turn our attention to the exhaust side. Any ideas on what Part Three will be about?

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