are you talking about over machining the turbine housing? The big wheeled k04 currently installed had that on its initial turbine housing. It definitely flowed better top end but suffered hugely on extra lag by , I reckon 750- 1000rpm over the normal clearance I run... While I think it possibly ran better at 7000rpm, EGTs being lower it was a dog at low range, more like a BT turbo, and added insult being the massive gt35 compressor didn't really flow until rpms where high made for a pretty lowesy unit. Now whether running a smaller compressor , more in keeping with the 2283 and extra turbine clearance has any benefit may be worth looking into.. What I do have about to be tested is the eliminator turbine housing , which has considerably larger a/r on the turbine but the same 40mm inlet, couple with a gt28 turbine and compressor capable of 380bhp, it'll be run on an xs manifold etc etc and it'll be interesting to see if that can produce better figures. I'll drop to a pm now as have something you may be interested in!