I know this has probably been answered before but for some reason when i search it deletes half the words in my sentence then searches.

I have a S5 turbo II motor, tranny, ECU and Wiring Harness, will a S5 TII driveshaft fit on a S4? Also, would a S5 differential fit on the rear end of an S4? If not would a whole S5 rear end fit right on?

 

Easiest way to do it is S4 NA harness. If you find one at pick a part make sure you mark all the connectors of where they go. Very important so you dont have injectors crossed up. Everything else is can be used minus the ECU cause the plugs are different and get S4 electronics. Boost pressure sensor, AFM, S4 Throttle Body with TPS and BAC Valve. You'll have to pre-mix unless you get a S4 TII front cover so you can us the OMP. Then you'll have to also can use the Drive shaft but if you rear end is a NA you would want to get a stepper bit to line up the holes cause the offset of the holes are different. You will have to extend the wires for the BAC Valve and possibly the TPS depending on how tight you have harness pulled. Make sure you get a all new belts and hoses and do a major tune up on it. JDM S5 engines the fuel lines are different so when changing the wiring harness follow the fuel line routing. The line to the primary fuel rail is in and from the secondary fuel rail on top is the return. Youll have a few sensors and things on the engine that WILL NOT BE USED!!!