The WORKS 02 sensor housing features OEM-quality cast construction and thermal-barrier coating. Mounting ears allow the use of the stock heat shield. A bigger radius and a larger interior volume provide superior flow. The WORKS housing is compatible with most aftermarket downpipes as well as the stock downpipe
When we last left Project Evo IX we had just tried out the most basic bolt-on mods and ended up being pretty pleased with the results, picking up nearly 30 whp from stock with just a few hours of work including dyno time. Driveability was improved as well, making it a win-win situation.
Of course, the power increase left us wanting more as our Evo's more than capable chassis didn't flinch with the additional power. Since we were just touching the tip of the proverbial iceberg in our path for more power, we ordered up more parts and got wrenching and testing.
The first thing on our list was to free up the exhaust some more. We were pretty shocked that the exhaust we installed in our last segment of Project Evo didn't make as big of a difference as we suspected. This meant that the stock Evo exhaust isn't that bad and additional restrictions probably existed upstream. We trekked to our favorite shop, Technosquare, and installed a WORKS O2 sensor housing, downpipe, and resonated race pipe to enlarge our exhaust system to 3 inches all the way to our GReddy TiC exhaust system.
The huge difference in the interior of the stock O2 housing versus the WORKS housing is shown here.
The WORKS O2 sensor housing replaces the stock cast-iron housing with a new cast housing that makes a more gentile bend out of the turbo for less backpressure causing turbulence while keeping a full 3-inch internal diameter through to the downpipe. Most O2 housings neck down to around 2.5 inches before merging with the downpipe. The WORKS housing's cast construction should be trouble free and its OEM-like fit allows the stock heat shield to bolt back in place for a stealthy install. With the supplied adapter ring, the housing works with the WORKS big downpipe, as well as stock and any other aftermarket downpipe. The housing comes coated with a gold ceramic thermo barrier coating to reduce engine compartment heat and resist corrosion.
The stock housing exit is much smaller than the WORKS full 3-inch exit. The WORKS housing has the largest exit of any aftermarket O2 sensor housing.
The O2 sensor housing led to the WORKS big 76mm downpipe. WORKS has taken a lot of care in designing the big downpipe to fit in the tight confines of the Evo IX undercarriage. When the Evo IX was introduced, its ACD torque control system caused fitment issues with many downpipes on the market, an issue many manufactures addressed by dimpling the pipe. Not so for the WORKS unit, it fits perfectly with plenty of clearance. It also fits perfectly with our CROX plate under-chassis brace. The many subtle bends in the downpipe can be seen for this reason. The downpipe is fabricated from 304 stainless steel tubing and has a coating of gold color thermo barrier to reduce heat soaking of the drivetrain. While we were under the car, Technosquare's ace fabricator, Richey Watanabe, welded in a Burns Stainless O2 sensor bung for our wideband sensor to make tuning the car easier and let us leave the stock O2 sensors in place while we tune.
To keep things quiet, we used a WORKS resonated race pipe to link the downpipe to the exhaust. With a 3-inch super free-flowing perforated core resonator, the race pipe is probably the reason why our exhaust system is pretty quiet. In fact installing these free-flowing parts seemed to make our already quiet car less noisy. The stainless steel race pipes matched the rest of our high-quality system.
The WORKS housing's less severe exit radius is shown here. This gives better flow from the turbo.
Evos are known to top out the fuel pump's capacity even with bolt-on mods. Although the Evo IX has a higher capacity pump than the Evo VIII, its pump still can get maxed out with bolt-ons. To prevent this from occurring, we installed what is rapidly becoming the industry standard fuel pump for turbo performance applications, a Walbro 255lph fuel pump. The Walbro pump is an easy direct bolt-on that takes only about a half hour to install. Walbro is a QS9000 certified OEM supplier so expect this pump to be extremely reliable.
Careful bending of the WORKS downpipe allows for clearance to the ACD housing found on the Evo IX. Many downpipes have fitment problems here. | 
Ritchie Watanabe of Technosquare TIG-welds in a Burns Stainless bung for a wideband O2 sensor into our downpipe. We added an extra bung to make tuning easier. | 
Here is the bung in place. |