After doing a thorough search I have the following questions. Please note, I do not own a 996TT, I'm just a 19 year old car enthusiast trying to soak up as much information as I can and this technology seems very cutting edge and very promising to your average boostaholic

First, the term zero clearance applies to the amount of space between the impeller and the housing. Now is this on both the turbine and the compressor or only on the hot side? Additionally, Kevin states that the diameter of the housing is approximately .012" larger than that of the wheel on standard non-zero clearance (making the distance from wheel to housing approx. .006"), but with zero clearance the difference in diameter is only about .002-.004" AMAZING! Am I right in assuming these turbos are more prone to seizing from neglect and abuse such as boosting before oil temperature has reached proper operating temp and shutting the car off soon after a hard run due to the tight tolerances? Kevin states that as wear sets in the gap gets bigger. Does this mean that the turbo eventually goes back to the same .006" gap? Finally, how much does this procedure typically cost over not having "zero clearance" done, and can this be done to non-Porsche turbochargers?

From searching, I found these excerpts from Kevin that I found helpful:

"The turbochargers start at zero... As they are VSR'd they seat in to the nominal bearing clearance. In the beginning they are Zero and nothing moves. You will see very shortly this proceedure coming out in OEM applications! The enngineering test have shown 10 to 15% jump in efficiencies. As wear sets in, the gaps do increase however, the static metal to metal is set at normal factory gaps. With the titanium billet wheels I can close the gaps even closer." and "It has nothing to do with the shaft to bearing clearance. It is the compressor wheel to compressor housing clearance. We are not on the same page. We are coating a housing after we CNC the compressor wheel into the compressor housing. The gap between the wheel and housing prior to coating is determined on what wheel we are running ie: Billet, Ti, Size and so on. We also CNC our own Backplates to set wheel depth. I will coat the housing to a zero clearance and go from there. And since we don't have carbon seals there is no tightness on start-up. I realize that you have been running Garretts for years, hell I give you the credit for patients. The 10-15% is coming again as stated from the factory test, on turbocharger dyno's.

The only benifit from a ball-bearing unit, is for the shaft centering ability, Garrett stresses the efficiency improvements on the GT series. This is due to the clearance being reduced. I'm taking this to a step further and getting it close to zero (minus my free float in my bearing stack)..

You do realize that if you close the gap between the two surfaces you will create efficiency. Then in theory, why can't we strive for a 100% efficient wheel. 100 air in with maximum compression with little heat due to friction and cavitation. We will never get these levels, but we will get higher numbers. Lets take for example the T28 ball-bearing Garrett, the published wheel specs for that turbo is higher than the standard SVO Mustang turbo that showed up 20 years ago. Why, the wheel is the same, hell, its the clearance, or lack of it....!"

thanks,

amir