Garrick Goh, Performance Parts Project Engineering Manager, and David Scelfo, Project Engineering Manager, review performance parts test data.
SPT parts must undergo exhaustive tests before they’re approved and released to market. The testing helps ensure performance, reliability, and durability. For example, SPT engineers recently conducted tests on air intakes (WRX and WRX STI – SOA8431000; Legacy GT and Outback XT – SOA8431010) and exhaust systems over a year’s time. SPT’s thorough testing included a variety of weather conditions and tens of thousands of miles in different vehicles across the country before the systems were approved.
Putting cars with these parts installed on a chassis dynamometer – the most basic engine-related performance-parts test – demonstrated whether or not the intake and exhaust systems provided more power. If not, the systems would have little value from a performance standpoint and would not be worthy of the SPT logo.
They found these new systems increased peak horsepower and torque across the rpm range compared to original equipment (OE). However, dynamometers don’t completely represent real-world driving, so several other tests were needed.
Extracting higher performance from an engine starts with the air it breathes. In general, the cooler the air, the better. Cooler, denser air improves performance because it has the ability to pack more air and fuel into the same space, resulting in a more explosive combustion, which translates into more power.
SPT heat shields were developed to separate the air intake from the hot air in the engine compartment. Combining SPT air intakes and heat shields (WRX and WRX STI – SOA8431030, Legacy GT and Outback XT – SOA8431040) resulted in reduced intake-air temperatures. Temperatures did not differ significantly from those measured using the OE air box.
Even during low-speed driving, intake-air temperature remained within a few degrees of ambient air temperature.
The mass airflow sensor (MAF) monitors the speed of air entering the engine and outputs a voltage for the engine’s electronic control unit (ECU) to use in determining the volume of available air and necessary fuel charge. For the MAF to function properly, airflow across it must be smooth, steady, and following a straight path. High turbulence can cause erratic voltage readings from the MAF. If turbulence occurs, then the ECU cannot accurately determine how much air is entering the engine and how much fuel to mix with the air, which can result in power loss and poor drivability.
SPT air intakes relocate the MAF sensors. Extensive testing was required to make sure the smooth airflow of the intake was compatible with the sensor. Tested in traffic, on the dynamometer, and under light and heavy loads at low and high speeds, the MAF output in the SPT intakes proved to be accurate because of the smooth airflow.
SPT air intakes also reposition the air filter within the engine compartment. If the air filter is positioned in a particularly turbulent part of the engine compartment, that turbulence can disturb airflow across the MAF and affect its output, causing its output voltage to spike. Tested at speeds well over the legal limit, the SPT intakes’ MAF voltages were as smooth as with the OE intake.
The engine ECU uses MAF voltage and the dimensions of the tube in which the MAF is positioned to calculate the amount of air entering the engine. Changing the intake’s shape or cross-section can lead to excessively rich or lean conditions. (Running rich causes damage to the emissions control system as well as the environment. Running lean can quickly ruin the engine itself.)
* The Power Pack consists of the SPT Performance Exhaust System, SPT High Flow Intake System, and SPT Heat Shield.
† As measured at the wheel.
Rich or lean conditions are measured by a wideband oxygen sensor, and the output can be converted to an air-to-fuel ratio (AFR). SPT engineers measured the AFR under normal and race conditions on the track and on the dynamometer and found that the SPT air intakes do not negatively affect the AFR.
SPT air intakes were subjected to the usual array of stringent environmental tests required by Subaru of America, Inc. These tests include hundreds of hours of continuous salt spray, temperature cycling, and soaking in various toxic chemicals. Against these conditions, the air intakes proved themselves ready to provide many satisfying years of service.
Once SPT engineers were satisfied with the performance of the air intakes, they were submitted to the California Air Resource Board (CARB) to be certified for sale in California, which has the toughest emissions regulations in the country. CARB testing results showed emissions from 60 to 99 percent below the legal limit!
Carefully designed and proven through numerous tests, SPT High Flow Air Intakes and exhaust systems qualify for the SPT badge. These parts not only provided improved performance, but do so without impacting the Subaru reputation for drivability, longevity, and reliability.