S5 ECU with an S4 turbo engine.
 

just wondering if the ECU will work because i was told it can handle more HP than the S4 turbo ECU. also, I heard the S5 ecu handles up to 250hp. just wanted to make sure it was true. thanks guys

The stock ECUs alone cannot handle much more then they're stock rating, moving from S4 to S5 is not the way to go. However, using an SAFC and 720cc injectors, you can get more just not as much as an aftermarket.

Also, you'll have to replace the entire wiring harness to move from S4 to S5 ECU, good luck with that.

ok thanks for the help

Not without a whole bunch of rewiring that will gain you absolutely nothing.

You were misinformed. In terms of pure engine performance both ECU's have about the same cababilities.

There are guys making much more than that on both S4 and S5 ECU's, but you need a lot more than just an ECU to do it.