>You lose a little thermal efficiency because the exhaust >gas isn't as hot. I've always been told the hotter the >gasses going into the turb the more efficient it will be. It's the Boyles law thing, PV/T, as you cool the gasses, they get denser, and the pressure and volume drop. You can partially compensate for this by changing the exhaust side turbine specs.
The other problem with remote mounting is increased turbo lag, as you have a much larger volume of plumbing to pressurize. Lag isn't as much of a concern for 1/4 milers, towing, or aircraft, but is for autocrossing or road racing.