Apologies, as the intent really wasn't to set you straight, but rather to say that the greater spool advantage comes from the rotating mass of the center assembly. I also had this discussion with a garrett tech at sema last year, and was told they had updated the wheel designs. Of course their site is down now, but they really dont have much real help there anyway...

I'm sure there's some data out there showing a difference in spool between same sized turbos with different bearing types, but it seems to be mostly marketing hype (in my opinion). The water cooled/longevity issue seems to be hype as well, as a dbb cartridge will roast without water cooling while a traditional cartridge wont.

The reason why Turbonetics uses a single ball bearing design is not because they don't have the technology to make a dbb cartridge... They have tested dual ball bearing turbos of their own but found that at higher rpms, dbb turbos display irregular harmonics/vibration that they were not comfortable with for longevity purposes. These exist on the garrett dbb designs as well. The ceramic ball bearing is also more durable than the traditional design garrett uses. The single ball bearing and 360deb journal bearing provides more stable shaft rotation while supposedly providing the advantages of a bb design. So, it's more of an issue of longevity than anything.


Still, after all is said and done. Wheel design and sizing is going to play MUCH more of an effect on spool difference between turbos, regardless of bearing style. The two turbos listed in the OP are quite different, just look at the wheel sizes. For that reason alone I'd say the GTK turbo will spool faster. I'd also say it totally depends on the target hp goal.