Holset Hx35 + Garrett T3 turbine housing advice & machining Q's

[mavericktsi83]

I'm currently researching my turbine housing options for use with the Holset HX35 7- blade turbo. I'm considering having the Garrett 5-bolt T3 housing (.63 or .82 a/r) machined to fit, but I'm unsure whether this combination would be optimal in relation to the Holset turbine wheel profile being a mismatch to the turbine housing geometry? From what I have read, it appears there is effectively NO difference between the BEP .55 a/r bolt-on housing and the larger T3 .63 a/r turbine housing in terms of spool-up and more significantly, flow potential. This is counter intuitive and may suggest a compromised design in the process of making it fit. Does anyone have any insight into the machining process (T3 Garrett) insofar as what might be causing the loss in performance? I understand the bore of the housing is enlarged and tight wheel to wall tolerances are crucial for efficiency (recommended spec?)...maybe the mismatch lies in the volute profile, radius, flow width, angle, etc...can all this be "reshaped" while maintaining "optimal geometry"? Thoughts?

I understand that there are 2 different castings of the Garrett 5-bolt T3 turbine housing, the "ford style" designed around older wheels such as the T31 and TH350 and a newer casting designed for the GT wheel technology. I'm not interested in the 3rd category of "Chinese" or knock-off style housings. Obviously all housings are not created equal, regardless of the a/r stamped on the side. Does anyone have any data (i.e., comparison, dyno, backpressure, airflow, spool, etc.) or know someone running the newer castings? Or anyone running the .82 a/r? I'm wondering how the the newer Garrett housing (either .63 or .82 a/r) would compliment the Holset considering they were redesigned (custom volute) around the larger Garrett GT wheels. I would also be interested in any data on the Garrett T3 turbine housing with the 3" v-band outlet. I'm looking for the best spooling housing that will max out the 60 lb/min compressor. I've searched...any links or first hand experience with any of the aforementioned housings in conjunction w/ the Holset would be much appreciated.

Thanks,
Mike