Optimum gas flow and minimal exhaust back pressure is essential for high power. The APS high output stainless steel exhaust system really performs.

Careful attention to tube diameter, smooth radius mandrel bends and muffler design is essential for high performance. With 20 years of experience in exhaust system design, we have built a superb exhaust system.   

Exhaust system design parameters immediately after the turbocharger are critical not only for outright performance, but for optimum torque and turbo response. The optimum internal profiles cannot be achieved with twin pipe or bell mouth pipes. APS has engineered the High Flow Turbo Outlet housing for extreme gas flow and high exhaust gas temperatures which are normal in high performance turbocharged engines. Cast in high temperature ductile iron ensures optimum internal shape and maximum durability under high rpm, load and boost conditions. 

The end result is an exhaust system that produces high outright power with stronger mid range torque than fabricated turbine outlet style exhausts. All this with improved turbo response (less lag) when running large turbochargers and maximum durability.

Careful attention has been paid to exhaust noise and note without compromising outright performance. A strong but subdued exhaust note with no drone at highway cruise and well matched to the dynamics of the WRX.

"How much horsepower will that exhaust system add?"

This is an often asked question, to which there is no real answer. An exhaust system is only a point of possible restriction, which needs to be reduced as required.

For example, in a best case scenario, total removal of the complete turbo back exhaust system from a stock MY01 225 hp WRX will result in a power increase of approximately 20 hp. On the other hand, on a 425 flywheel hp WRX, utilization of the correct exhaust system would literally represent 65 of the 200 hp increase over standard.

A good starting point for the correct choice of an exhaust system, the following should be used as a useful giude:

1. Street Use - Legal Emissions/Noise - Less than 4.0 psi back pressure
2. Street Use - No Legaility Issues - Less than 2.5 psi back pressure
3. Race Use - As low as possible, however no more than 1.0 psi back pressure

The following chart provides exhaust back pressure data for a given engine power level for the stock WRX exhaust system as well as the range of APS High Output exhaust systems.

Selection of the correct WRX or STI exhaust systems is the appropriate combination of back pressure, catalytic convertor and noise to suit the engine's power output.