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.