The center cartridge is often taken for granted as much of the attention when it comes to turbochargers is focused on housing sizes and wheel trims. The center section is the "durability center" of a turbo. Lubrication and cooling of the unit happens here and if things go bad, it's game over. There's no doubt that ball-bearing cartridges have been a godsend for turbo enthusiasts. Almost like cheating, tuners are using the ball-bearing design's quick spool-up to negate turbo lag and to run bigger units on smaller applications.
Garrett's dual ball-bearing turbos were originally designed for diesel engines. Diesels were known to produce throttle tip-in smoking. The smoke was the byproduct of a rich condition that occurs after the throttle is opened, but before boost is realized. Response was the goal because diesels don't rev very high. So ball-bearing turbos designed to spool-up quickly were developed that shortened the time between the pedal and the boost, which helped solve the problem. The highly responsive design was perfect for extreme motorsport applications, which eventually led to the HKS/Garrett GT lineup now seen on the street, as well as offerings from Turbonetics and other manufacturers.
In the first of this two-part article, we'll examine the inner workings of the center cartridge to develop a basic understanding of its functions. In the next installment, we'll explore the different types of ball-bearing center sections.
Learn how the center cartridge works as we assemble a conventional journal center section and outline some of the differences between journal bearings and Turbonetics single ball-bearing center sections.
The difference can be seen in the palm of your hand. It's all about stability and friction resistance; the ball bearing easily outshines the journal bearing in both aspects. Turbonetics reports that its single ceramic ball-bearing design spools 25 percent faster than a journal setup, while delivering 50 times greater thrust resistance. | 
Here's a conventional journal-bearing center section setup. On the left, a 270-degree thrust bearing and brass journal bearing. | 
This is the Turbonetics single-ball-bearing center cartridge. It features a beefier thrust bearing, a 360-degree washer and an angular-contact ceramic ball bearing. |
Small but important, these retainer clips slip into ridges inside the center section and keep the bearing(s) in place within the cartridge. | 
Next, the bearing is dropped in the housing. In this picture, it's a journal-style unit. | 
Then the thrust bearing and the washer are put together. The thrust-bearing assembly is positioned on the housing. The dowels are used to properly line up the assembly with the oil passages in the cartridge housing. |
The thrust bearing is one of the prime areas of failure. Ever wonder why oil changes are more frequent for turbocharged cars? Note the three oil ports and pads on the thrust bearing washer (arrows). Everything is riding on the thin layers of oil provided by these orifices. | 
Here, the center cartridge is ready for the addition of the backing plate. |  |
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In journal bearing applications, a retaining clip is inserted in the backing plate, which is secured with four bolts. | |
The 270 vs. 360 Dilemma
Many conventional journal- bearing turbos use a 270-degree thrust-bearing washer (at left), while the new breed of conventional and ball-bearing turbos employ 360-degree thrust bearings. The advantages of a 360-degree bearing include a full circle of lubrication, six orifices on the washer instead of three for the 270-degree unit, and an updated pad strategy to better disperse oil where it's needed. Turbonetics uses 360-degree bearings on all of its T04B and T04E turbochargers. There isn't much of a dilemma here; if you have the opportunity to use a 360-degree bearing, jump at it.