APS S/R Series Ball Bearing Turbochargers
Technical Information
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A turbocharger is simply a device that pumps air and is designed to operate within a defined envelope of parameter ranges - namely boost pressure, air flow rate and turbine shaft rotational speed. A combination of these parameters results in an efficiency that has a direct bearing on the temperature of air that the turbocharger compressor supplies. Turbocharger efficiency is essentially the ratio of useful work produced by the turbocharger from the work required to drive the turbocharger. An increase in temperature is of course a by product of compressing air and is unavoidable. The efficiency is typically displayed as a fraction where an efficiency of 1.0 is ideal. It is typically accepted that an efficiency of 0.6 is the lowest operational limit. Naturally the maximum rotational speed of the turbocharger rotating assembly (the turbocharger's red-line) is also a limiting factor. Turbocharger designers strive to achieve high air flow rates at reasonable boost pressure levels with a high efficiency. A higher turbocharger compressor efficiency value means lower charge air temperature. Naturally, lower charge air temperatures assists in improved engine durability with the potential to achieve even higher power and torque output. When mapping boost pressure versus air flow rate versus efficiency, a 3-Dimensional surface is produced and the charts below reflect this. The following charts are a representation of the turbocharger performance envelopes of the various APS turbocharger compressors with comparisons to well known turbochargers where appropriate. The charts display boost pressure (psi) versus mass air delivery (converted to horsepower) versus compressor efficiency.
Standard TD04 Turbocharger
 The Standard TD04 turbocharger installed on the WRX is well matched to the required power output of the stock WRX. At 220 hp - 230 hp and around 13 psi of boost pressure, the TD04 is within its limits and with the potential to supply enough air to produce 280 hp. Typical of any turbocharger, as boost pressure is increased past the point where peak air flow is produced (at around 19 psi of boost pressure), air flow, hence horsepower decreases.
APS SR30 Turbocharger
 With the choice of 2 different turbine housings, the turbocharger response characteristics can be fine tuned for street or strip.
APS SR30 turbocharger versus Standard TD04 turbocharger
 The chart above shows the TD04 performance envelope inside that of the SR30 turbocharger (see through envelope). The APS SR30 turbocharger offers not only significantly improved air flow capacity over the TD04 but also a much greater operational range. Where the TD04 has a maximum air flow capacity to produce 280 hp, the SR30 offers 340 hp. The chart below shows a clearer view of the inside of the TD04 and SR30 envelopes. 
APS SR30 turbocharger versus VF22 turbocharger
 The above chart shows the highest performing VF Series turbocharger performance envelope inside that of the SR30 turbocharger (see through envelope). Whilst the SR30 offers similar air flow capacity to the VF22, the most striking fact is that the SR30 turbocharger provides a much wider operational range. What can't be seen in these charts is the fact that the SR30 offers higher durability than the VF22 particularly as the boost and air flow limits are approached. The chart below shows a clearer view of the inside of the SR30 and VF22 envelopes.
APS SR40 Turbocharger
APS SR40 turbocharger versus PE1820 turbocharger
The chart above shows the performance envelope of the PE1820 (colored grey for clarity) compared to the APS SR40. Prior to the release of the APS SR series turbocharger range, the PE1820 turbocharger with its good blend of performance and turbocharger response was seen as the "hot" turbo for heavily modified street and strip WRX engines. APS has now rewritten the rule book with the SR40 turbocharger. With crisp turbocharger response and more outright power than the PE1820, the SR40 provides the WRX performance enthusiast with the power to stay ahead of the competition. As can be seen from the charts above and below, the APS SR40 provides more air for greater power and torque above the 400 hp level.
The chart above shows the inside of the performance envelope of the PE1820 (colored grey for clarity) and APS SR40 turbochargers.
APS SR50 Turbocharger
 With the choice of 2 different turbine housings, the turbocharger response characteristics can be fine tuned to suit a wide range of race track conditions.
Looking inside the performance envelopes of the range of turbochargers
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