I was wondering what the difference made in the different choices and combos you can do with the a/r on a turbo and the hot side size i believe it is ?

 

if your asking what is the end result of changing your turbine housing (hotside) then it can be pretty much summed up like this:

smaller turbine housing: spools faster, can limit your max power, too small can choke up your higher rpm
large turbine housing: shifts your powerband higher up (possilbility of making more topend power), but can increase lag.

the idea is to find a good match depending on your vehicles intended use, for more info check out turbobygarrett.com