1. The stock curve is reasonably representative of Subaru's claims when run on 93 R+M/2 Octane fuel.
2. The second curve illustrates the gain (20 hp max) to be obtained by the installation of the full APS turbo Back exhaust system. The stock cat back components are quite efficient at stock power levels, hence opting for an aftermarket cat back system is of little benefit in terms of power increase.
3. The third curve illustrates the benefit achieved through installation of the re-calibrated APS plug-in engine management unit. As can be seen from the boost curve, there has been significant remapping in this area. However, the most significant feature of the boost curve is the way it returns to stock at redline. This is simply the result of insufficient air mass flow through the stock air element assembly/turbocharger compressor.
4. The fourth curve illustrates the effect of installing the APS Cold Air Intake System. Although boost has not altered, peak power rises and more importantly is held out to redline. This is a result of significantly reducing the restriction created by the stock air cleaner assembly. This permits later gear changes and results in superior acceleration by keeping the engine more within its maximum power band.
5. The fifth curve illustrates the result of installing the APS DR525 Front Mount Intercooler System. This has effectively eliminated any system pressure drop between the air cleaner element and the throttle body. In other words, from the turbocharger compressor's point of view, this is as good as it gets! As can be seen from the curve, the engine is producing 370 hp (flywheel), however the peak point has dropped to 5,000 RPM - A sure fire indicator of insufficient compressor mass flow. There is only one way to go from this point - and that is to install a larger turbocharger.