Going Faster - Engine and Drivetrain Modifications

Here is your complete guide to getting more horsepower from your WRX motor.

The Subaru EJ20 turbo 2.0-liter motor is an amazing high-tech power plant with a huge capacity for increased performance.

To unleash the increased power from your turbo-charged motor, you need to allow the turbocharger to breath more freely, on both the intake and exhaust sides of the motor. Generally, you should start from the ends of the system and work inward. When you have opened up the intake and exhaust as much as you can, you can switch to a larger turbocharger for even more power. Then there are additional ways to add power to the motor, including electronic add-ons.

Mild Modifications Here we bolt on the simple modifications. These are generally easy to install and get some quick horsepower, but they don't change the basic nature of the car. It remains civil and easy to live with; it just has 30% more horsepower. High Flow Intake This used to be an easy way for owners of turbocharged cars to add gobs of power. Just slap an open-element air filter on a turbo Eclipse, for example, and you get an instant 10 or 15 horsepower. Technology advances, though, and the newest factory-built intakes are much better. Horsepower gains from intake systems on the WRX are smaller, but there still are a few horsepower (maybe 5) to be gained, and as other modifications increase, the added power will go up as well.

Downpipe & Catalytic Converter The front two sections of the turbo-back exhaust are the downpipe and the front-mid pipe. The downpipe bolts directly to the turbocharger outlet, and collects exhaust gas from the turbine wheel as well as the wastegate. The wastegate outlet part of the downpipe has one of the worst layouts ever in exhaust-dom, with the wastegate gas running directly into a flat plate. That gas has to somehow find its way over to the main section of the downpipe. It's obviously not a high-flow layout, so upgrading this pipe is great for performance, as well as for preventing "boost creep" (uncontrolled increases in boost) from poor wastegate flow. The factory downpipe has a catalytic converter in it. Some aftermarket downpipes also do. Some don't. A cat-less downpipe will generally out-flow one with a catalytic converter in it. The front-mid pipe has a catalytic converter after it. Many manufacturers offer larger-diameter replacement pipes with higher-flowing catalytic converter sections, or with no catalytic converter. It's good to keep at least one cat in the systems for a lot of reasons, one of which is good citizenship and keeping the air clean. Another is that there are two oxygen sensors in the exhaust system, and having a cat between them keeps the ECU happy and not throwing "Check Engine" lights.

Boost Controller or ECU Upgrade

At this point we add power by increasing the turbo boost pressure. There are two ways of doing this, both of which have some tradeoffs.

The "easy" way is with a boost controller. You basically remove turbo boost control from the car, and put it in the hands of a mechanical or eletronic device that YOU set, so you can specify whatever boost pressure you want. The benefits of this are complete control, low price, and ease of install and use.

The downsides are...well, possible destruction of your motor if you aren't careful. Sending too much pressurized air into the motor, especially at high rpms, can have very serious consequences.

The other approach is to get an ECU upgrade. This will increase boost levels, as well as change a whole bunch of other stuff, including timing maps, rev limits, speed governers (bye bye!), and more. The benefits are that you get a known-quantity ECU program with proven results, and you get the most horsepower you'll probably be able to make with a certain set of modifications on the car.