My understanding is that ball-bearing centers have very little to do with full-boost rpm (a ball-bearing center isn't going to make a turbo push 20 psi at 3700 rpm instead of 4000 rpm) but are all about transient response- the time from 0 boost to full boost when you're in the meat of the turbo's effective range. So a ball-bearing turbo won't drop your full-boost rpm from 4000, but if you are cruising at 4500 and go WOT the ball-bearing turbo will spin up to full boost almost instantly. This sound accurate?

 

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.

 

Yes, that sounds accurate and can be backed-up by the graphs showing the difference in spool up between the two...they both end up at the same peak RPM.

Some kickass articles I found and read:
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Note that the following two are from 2002, above are from 2006:
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Punx: I love learning new things, especially when this is the field of engineering I'd like to go in to...I feel sorta stupid now looking at it...its pretty far above me

 

I have an old school Turbonetics T-Series Journal Bearing. It was cheap and durable from what I gathered from my research. I have been road racing it for a year. I am very happy. When deciding on my turbo purchase, I weighed Garret to Turbonetics. Turbonetics was less expensive, a work horse, and I liked the fact that they had their compressor maps easily accessible online (Garret from what I remember was limited in regards to their published material). I couldn't find any hard core data on response time difference between journal and BB. Is BB a faster spool? Of course. But how much faster is it? Seat of the pants is great, but when another couple hundred dollars is dependent on what, a couple hundred rpms in response, I am indifferent because I am above 4000rpms around the track anyways. Does this spool response matter to drag racers? I'm sure. My .02

 

I'd love to see the articles you're referring to. All the turbo companies have huge claims for "xx% faster spooling ball bearing turbos" but none really provide real world proof of the degree of improved spool.

I agree that what he said sounds more accurate. As far as the degree of difference between a dual and single ball bearing turbos, I think you'd be splitting hairs...

Oh, and I love having these discussions even if I'm told I'm wrong. It's the best way to learn.

 

I have heard this several times most recent was a guy out of south FL "Mike from USP Motor Sports" He went through 3 of the BW turbos with in a month or two then decided to go back with a GT42r and hasnt had a problem since putting it on.

 

yessss....quite

 

I'm currently running a GTK-854/650 hybrid turbo with water cooled jacket (a bit smaller turbo). You can get a turbo custom built if you contact a Turbonetics dealer and specify whatever specific features you need.[/QUOTE]punx

did the water jacket improve the performance of the turbo?do they charge extra for that option?

 

No, it doesn't alter the performance of the turbo in any way. It alleviates the need to cool the turbo down via turbo timer, and prolongs the life of the bearings and seals.

 

^^ said turbo timer... That is a whole other discussion