Typically the aftermarket has a few generic compressor housings that they carve out the inducers and blade areas to fit a wide variety of wheel designs. Optimized compressor wheels are nothing if they are not placed into a properly designed housing. Garrett compressor housings are CFD optimized for the wheel with the correct volute geometry, diffuser width and height for the pressure ratio and flow desired. Garrett housings like this can also come with ported shrouds to add more margin at the surge line allowing the turbo to resist surge at high boost low flow situations like a responsive fast spooling turbo making a lot of boost at low rpm. The port size and geometry is determined through CFD analysis as well. After the performance engineering is done, the housing must also pass through durability and burst containment testing.
Although there are other companies that produce good turbos that reliably make power on the market, we as well as a lot of OEM manufacturers have a lot of confidence in Garrett turbos due to their intensive engineering and testing using resources that most of the aftermarket can only dream of affording. When the OEM's try to stretch every dollar in the name of profitability and where a lot of warranty problems can greatly affect the bottom line and customer satisfaction, they look towards Garretts' engineering to come up with designs optimized for their requirements. In professional Motorsports, Garrett for this reason also has a very high penetration rate in motorsports that require a decent amount of durability as well as efficient power.
It's all in the engineering! Stay tuned as we explore other aspects of Garrett's engineering in features to come.