While the Aurora 2000 turbo's overall size is fairly similar to the factory unit, the internals are vastly different to improve efficiency and reduce operating temperatures for better airflow.
The thing that makes a turbocharged diesel such a wonderful engine really comes down to the interaction between two simple things: air and fuel. The more diesel fuel you can burn, the more power you'll have on tap, and that requires pushing as much air as possible into the cylinders-which is where the turbo comes into play.
As most of you already know, expanding hot gases from the engine's exhaust manifold(s) spin the turbocharger's turbine wheel, causing it to turn the compressor wheel. The compressor, basically an air pump, creates boost that pressurizes the engine's intake. This increased airflow to the engine improves the efficiency of the burn cycle, with the end result being increased power output and lower exhaust gas temperatures.
Removing the stock Holset HX35 turbo is a fairly simple process. It unbolts from the four-bolt flange on the exhaust manifold and requires disconnecting a few hoses and the oil line. Rob Hancock and Betty Sutherland pitched in to help with the swap.
Of course, not all turbos are created equal. Some push more air than others because of their size and design, and depending on the application, bigger isn't necessarily better. For instance, the 12-valve Cummins-powered '96 Dodge Ram we used for this article is primarily a work truck used for towing boats over fairly long distances-not bombing down the dragstrip. So while more horsepower is welcome, extra torque is necessary for this particular truck. Clint Cannon, president of ATS Diesel, points out that for towing and hauling, an output of up to 450 hp is ideal, but higher levels are more for sport and competition applications.
Choosing A TurboWhen it came time to upgrade the stock Holset HX35 turbo on our Cummins, we chose the Aurora 2000. ATS offers five different levels of turbochargers and has just introduced a new compound dual-turbo kit. As much as we like the sound of two high-performance pinwheels on a diesel, this truck's got a job to do, so we opted for somewhat more modest gains. The Aurora 2000 turbo is designed for fast response and improved low and midrange torque while reducing EGT and maintaining good fuel economy.
Showing the Holset HX35 next to the ATS Aurora 2000 turbo reveals several differences. The lack of a wastegate on the Aurora is the most obvious one, but there are several others. Note how the Aurora's discharge outlet is larger and has a slightly different exit angle. The Aurora's outlet allows air to exit more quickly from the compressor wheel and have a more direct flow with less restriction and no turns, reducing heat and pressure, which can rob performance. | 
Note the gap in the compressor housing inlet of the Aurora turbo. This inducer, or bleed ring, enhances the width of the boost map, partly by allowing the secondary vanes to grasp more air. | 
The shape of the Aurora's compressor blades, its extended tips, and its steeper pitch all work together to improve the airflow. Little changes make a big difference. |