Turbo housing

Hi everyone, I am trying to create a turbo housing (exterior shell). I started by creating a section for the snail shell using a method for a spring but when you try to scale one end of the spiral the shape flattens off in the middle which is incorrect. I also tried creating the spiral shape of the snail like structure using a set of scaled circles and then lofting them which kind of worked but again the results of the curve in the model didn’t come out absolutely like I wanted them. Does any body have any other ideas on how to create a better turbo shell like structure?

After lots of messing about, I finally made a basic turbo exterior shell (one side) hopefully to use the “shell tool” in shapr but when it try to apply the tool shapr can’t perform the function as it says it will give an invalid result, which suggests to me that my model has issues with bad topology. Are there any clean up model functions in shapr, or any tool that tells you exactly what is wrong with a model. I come from a 3d back ground mostly with Maya and Max. Thanks for any help given.

A few pictures would help us to understand your problems. And maybe we all could help?