I'm guessing you mean the turbine inlet. It will get as hot as your pyrometer reads if it's held there for a decent amount of time. I'm not sure on a minimum clearance but I'd say around 1.5". If you're that worried you could get it ceramic coated.
Lee, get it coated. It helps, and isn't that pricey, escpecially on these motors, where you're not spending a lot of dough on all the stuff you buy for gas motors. I'm getting the manifold and outlet housing, as well as the downpipe, coated..
Mostly, my clearances are kind of tight the way I'm doing it, and I want the best fighting chance to beat heat that I can get.