Jun 21, 2010 update to the Subaru WRX project car

Piping-Hot Performance

The most challenging part of upgrading the WRX exhaust was removing the factory heat shields. Patience and observation are key.
Removing the intercooler made accessing the downpipe much easier. The flow is probably less than ideal through these plastic ducts, so we've got our eye on future improvements in this area as well.
Once the downpipe attachment bolts were exposed, the job got easier.
It's very clear to see why our downpipe from Moore Performance offers better performance than the stock unit. Aside from better materials and larger diameter piping, the wastegate now has a direct path for exhaust flow.
The 3-inch Moore Performance exhaust should provide all the flow potential we need for future upgrades.
Slip-joint construction makes aligning the exhaust a no-brainer.
Quality welds and thick flanges mean that the Moore Performance uppipe is as simple and effective as it should be.

Exhaust upgrades are a great starting point for any turbocharged car—especially an early WRX model like ours. Moore Performance & Race Parts sent us one of their 3-inch stainless exhaust systems for testing, so why wouldn’t we bolt it on and try it out?

Before installation, we ran some baseline acceleration tests to measure the new system’s effectiveness. Using a calibrated, professional accelerometer, we tested the car’s acceleration from 20 to 50 mph. This method removes variables such as shifting and traction, making it a more accurate measurement of engine power than a zero-to-60 test.

Like most factory exhaust systems, the stock pieces were heavy and didn’t promote the easy breathing flow characteristics that allow for more power. This was especially true of the factory downpipe, where exhaust gasses are routed from the turbocharger itself. The Moore Performance piece uses a separate 2-inch tube for the turbocharger wastegate, which they say promotes better exhaust flow and prevents turbulence around the wastegate itself. This, in turn, should provide better boost control.

A less common modification—but one of particular importance for owners of early WRX models like ours—is replacing the factory uppipe. This seemingly simple piece connects the exhaust manifold to the turbine inlet, where the heat and pressure of the exhaust spin the turbine itself. Early model WRXs are equipped with a small pre-catalyst in the uppipe to help with cold-start emissions readings.

We’ve studied catalysts and their effect on performance, and we don’t normally condone their removal. Unfortunately, when these units eventually fail, they have been known to send debris from the failing catalyst structure through the exhaust stream and directly into the very hot, very fast-spinning turbine. This will turn your high-precision turbocharger into a nifty paperweight.

An ounce of prevention beats a pound of cure, so we chose to replace the factory uppipe. As a bonus, the higher flow heat and gas flow are reported to improve the rate at which the turbocharger spools up to create boost. Faster spool means a faster car, so how could we complain?

Installing the parts was more time-consuming than difficult, but it pays to take your time. Getting some buddies together on a weekend can make short work of the process. The Moore Performance parts were a snap to install, as most of the system uses a slip-fit, banded-clamp construction that allows a great deal of control over the physical location of the exhaust. This prevents any rattling or unwanted chassis contact.

The Moore Performance exhaust is constructed completely from 304 stainless steel and features big, strong flanges to ensure a long service life. Seriously, the stuff screams quality. In an age where consumers can order an exhaust system that’s sold as “stainless steel” but feels soda-can flimsy, it’s nice to have a product that feels as well made and durable as these.

In the end, though, we made this upgrade in search of more power, so once installation was complete we eagerly measured our gains. Our next round of acceleration tests revealed that we were indeed making gains; the run from 20 to 50 took only 4.03 seconds, an improvement of nearly a full second. To put it in perspective, that’s nearly 20 percent quicker with no other modifications. We told you that turbocharged cars respond well to an open exhaust, right?

Subaru’s boxer engines have a polarizing effect on enthusiasts; those who like the rumble of a flat-four seem to like them at any volume, while some folks simply don’t care for the noise. If you’re among those who enjoy a snarly, whistling beast—you’re in luck. Our WRX sounds downright racy, especially under load at wide-open throttle. We’re looking for a nice, long tunnel in the area for a late-night session of the internal combustion opera.

Of course, this just opens the Pandora’s box of modifications that much wider. We’re expecting the Subaru ECU to wise up to our antics any moment now and illumintate the check engine light thanks to wildly altered flow characteristics and a now-missing temperature sensor from the uppipe’s pre-catalyst.

Again, the aftermarket shall provide. Stay tuned as we investigate the expanding frontier of open source tuning tools. We’ve also got some driveline maintenance to do, so look for freshened hubs, bearings and brakes in future updates.

We’re always looking for your feedback, so if there’s something you’d like to see us try or evaluate, post a comment below or drop us an e-mail and tell us all about it.

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