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SPT Parts for the 2008 Impreza WRX



The test subject was a hand-built, prototype 2008 Impreza WRX 5-Door. An early build of that model, it was continuously brought closer to what the final manufactured product would be. It did not have a production engine control unit or wastegate actuator hose, so Mr. Watanabe brought these production parts with him from Japan to be installed prior to testing to help ensure test accuracy.


In addition, the WRX wore a number of 2008 accessories, including a mesh grille, rear bumper protector, and boost gauge.




Original equipment and prototype exhaust systems were
tested for airflow capacity.


The team tested to confirm that the parts would add to the power developed by the WRX engine while still falling within emissions and sound regulations. The team charted Yoshikazu Watanabe’s required measurements at specific engine speeds.


Testing to determine if the prototypes provided increased airflow entailed mounting all original equipment (OE) and prototype intake and exhaust components on an airflow measuring device and recording capacity. That and some work with the production engine control unit took the better part of an afternoon. Each system had to be rigged separately to the airflow machine, often requiring parts to be removed from the prototype 5-Door.


At the airport, the team measured decibel levels from the car fitted with the prototype Power Pack. From 15 meters, microphones measured sound emitted at wide-open throttle while accelerating in second and third gears. Multiple passes were made by the car fitted with the different combinations of components. Also, the noise level measured directly behind the car while it was revving ensured that it was below 93 decibels. The exhaust system with the right Boxer engine sound passed the tests within set limits.


Testing on the Church Automotive Testing dynamometer proved that the prototype intake and exhaust systems added horsepower and torque over the OE components. The dyno also measured emissions, boost, and other parameters. In addition to pulls to red line, the dyno provided measurements while holding constant a number of specific engine speeds.


One test result was the modification of the pipe's cross section where the mass airflow sensor in the intake system. It was changed to allow measurements for safe air/fuel ratios otherwise the mixtures would have been excessively lean.


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