The most important part of the Stage III kit is the exhaust manifold. APR has spent enormous time and resources developing the turbo manifold. The exhaust manifold has been designed in Pro/Engineer 20, a 3-D modeling package and validated extensively on the computer using Exa Powerflow, a CFD analysis program. By performing a computational fluid dynamics analysis, they were able to study exhaust flow, pressure drops, and fluid flow through the exhaust manifold. Multiple computer simulations were done to prove the design before we even had a physical manifold in hand.

Once the manifold was fully passed on the computer they had the exhaust manifold CAD file transferred to a rapid prototyping machine. A polycarbonate exhaust manifold was cast from the prototyping machine. With this plastic manifold APR was able to mock everything up in the test vehicle before proceeding to the next process.

From the polycarbonate piece they were able to cast a metal piece for prototyping. The metal used for the prototype and the production manifold is Inconel 625. Inconel is a very high quality (yet expensive and difficult to machine) metal that is used extensively in the racing and aeronautical industry (Audi Sport sells an Inconel exhaust manifold for $10,000). Inconel has excellent heat retention characteristics that work to enhance turbo response by keeping exhaust velocities high. We guarantee that this manifold will never crack. Furthermore, the production manifold is cast using a lost-wax process versus a traditional sand-casting process. This process is more expensive but gives a much higher quality part with better tolerances, no parting lines, and a smoother surface finish (the internal surfaces feel like they have been Extrude Honed).

The exhaust manifold is mated to a Garrett turbocharger that replaces the stock Triple K K03 turbocharger. APR chose to use a Garrett turbocharger in lieu of a Triple K unit for several reasons. First of all, the new Garrett GT-Series is a more efficient design than the old Triple K K-24 turbocharger used by one of their competitors (the K-24's design dates back to the mid 70's). The Garrett turbocharger APR selected is a 1990's design. Also, Garrett turbochargers are available in a wider variety of configurations than the Triple K line, which allowed APR to find a more exact match. The stock injectors are maxed out at power levels much over 220HP and consequently the fuel injectors have been replaced by larger units. Dialing in the injectors required many hours on the chassis dynamometer to achieve the proper fuel mixture throughout the entire rpm range.