[FerociousP]

The engine has more stock HP because of the s5 specific parts like ecu, VDI, and higher compression. As you cannot use s5 manifolds in an s4 car without disabling the VDI, and you are using an s4 ecu, you will only be seeing the benefits of the high compression, which will not grant you the 20hp difference between stock s4 and s5 motors. there are other minor differences but they are just that... minor.


You know you have an s5 if:
- If the UIM has four tubular pipes instead of the "brick" style right after the throttle body.
- If the TPS has two sensors instead of one.
- If the OMP is electrically controlled
- If it has no EGR valve on the top of the shortblock

With that said, if the motor was rebuilt then it could have weird internals, lower compression rotors, etc... but if all those possibilities are there then most likely you have yourself an s5.