After searching for a while for what must be a noob question, I now ask it, since it seems to be unwritten here. What is the TII's turbo from the factory?

 

S5 TII is a Hitachi HT-18.
The S4 is something a bit different, but I can't remember its model # exactly.
=a

 

is there a difference in size, and if so are the s5's bolt ons to the s4's?

 

The S5 turbo bolts to the S4 engine if you use the S5 manifold. So the manifold must match the turbo. Each series of turbo has a different mounting flange. For into, search for "S5 turbo swap".

 

The FC's all use a Hitachi HT-18 (size) turbo.
The turbos are physically identical except for the turbine housing (and the oil drain pipe).
In fact, you can swap the CHRA's and compressor housings, and it'll all fit; something of a trick, if you're trying to save your precious S5 turbo.

No, the turbine flanges are proprietary; they do not bolt onto anything else out there.


-Ted