Not to change the subject matter of using a turbo, but have you considered a Vortech or Paxton, or possibly even a Procharger centrifugal supercharger instead. They dont have lag or other issues that a turbos has such as excessive heat buildup(I don't think I'd want it close to gas tank,unless you wrapped it), and would be easier to mount, even in your application. Increasing boost is just a pulley change away(6psi-20psi+).The drag on the engine,even though it is pulley driven, will be insignificant compared to the results of power increase. I have seen some trucks with a turbo mounted in a "fake" tool box that was real stealthy. But the fabrication costs alone were several grand by itself.And whether the power results were conclusive with all that extra length of tubing was undetermined! So im sure that the installation cost would be comparable for mounting one even farther back in a vehicle, unless you can do most of it yourself. I didn't know if you were dead set on using a turbo, or had some other reason....
