2008 Subaru WRX Project - Tech

When it comes to fast streetcars, low-rpm torque is king. It's low-rpm torque that lets a car initially pull away from a light or pass on the highway with just a tip of the throttle and no downshift. That's why nothing beats a big pushrod V-8 when it comes to stoplight racing. (Not that we would know anything about that.) Project WRX offers the next best thing: A fast-spooling turbo matched to an engine that moves plenty of air at very low engine speeds with relatively low redline. This means our turbo spools instantly and provides the most air where the engine wants to make torque, before 5,252 rpm. The compressor and turbine on the stock turbine maxes out just shortly after that, but by then you're probably already at the next light. Low-end grunt means faster acceleration without having to wait for boost or the need to slip a clutch in order to launch the car without bogging. Even though Subaru decided to put a larger turbo on the '09 WRX, we're going to stick with our stock dinky but lightning-fast hair dryer that can come to peak torque before 3,000 rpm while still making decent power. It's like having rally car response without the inlet restrictor and anti-lag.

So far we've done little to the engine other than a bolt-on intake and exhaust, which seems to increase torque output more than anything else. So the car likes to make torque. Before updating the ECU tuning for more boost and slightly leaner mixtures, we added two critical components for any bolt-on Subaru build to maximize what we get out of the stock turbo.

Down Pipe
On the exhaust side, we dumped the stock downpipe for a Cobb Tuning stainless steel 3-inch piece that runs all the way from the turbine outlet to the beginning of the B-pipe on the exhaust. Replacing the stock downpipe also means that the stock catalytic converter comes out. Luckily, Cobb's downpipe comes with an integrated metal substrate high-flow catalyst that in itself is supposed to flow as well if not better than stock while offering the same ground clearance as stock. The main advantage of the downpipe is the high-quality cast five-bolt inlet housing that bolts onto the turbine outlet and is beautifully welded to the 3-inch piping. The inlet housing replaces the stock unit's mass production flat plate design with a smooth blended transition that allows gases coming from an open wastegate to merge with the main turbine exhaust flow instead of slamming into the stock flange plate, making two 90-degree turns and causing a lot of turbulence and ultimately back pressure. The larger 3-inch piping, which all together weighs in at 12.5 pounds instead of the stock's 20 pounds, also helps move a lot more exhaust gas.

Our only gripe is that the downpipe pinches down to a 2.5-inch diameter right after the high-flow cat so that Cobb's unit will bolt onto a stock exhaust. For the same reason, our exhaust pinches down to 2.5 inches at the very front so that it could bolt onto a stock downpipe. This means we essentially have a useless 2.5-inch pinch right in the middle of the exhaust piping. We'll leave it alone for now since our stock turbo doesn't have enough high-rpm flow rate warrant going to a fabricator to get this addressed.