Is there any reason why a S5 motor won't work in a S4. Trying to sell a S5 motor guy has a S4 will it work? Thanks

 

harness and ECU are going to be nessary along with i belive a few other things i know the s5 radiator are different as well...i belive the hardest part is getting the new engine and dash harnesses in? correct me if im wrong!

 

It will work, however, it will need the front cover and MOP from the S4 and then use the S4 ECU and harness... and if it is a S4 non turbo, then build a couple of circuits for RPM control on the VDI and aux ports.

Or use the S5 harness and ECU, and then custom build a couple of plugs to mate the S5 engine harness to the S4 front body harness

Or use the S5 engine harness and the S5 ECU and the S5 interior harnesses and electronics.