What is the difference between the S4 NA housings, S4 T2 housings and also with the S5 set ups?

Is it just the knock sensor holes and the defusers? What makes them different?

 

S4 housings diff between na and turbo. difusser, and no coolent hole in housing ( the turbo ones have a hole like the 12a housings)

s5 housings diff are difussers, coolent hole, and knock sensor hole ( s4 has knock sensor on center iron.)

now diff between all s5 housings and s4 housings the spark plug locations are actually a little bit different which changes the timing!

 

So, what kind of problems, if any, could you expect if someone rebuilt an S5 engine, replacing the rear rotor housing with an S4 (Hiroshima)?

 

Bad timing. Misaligned sparkplug holes.

NA housings can be easily swapped to turbo. Drill out the coolant feed port and switch the difuser out.