I have an s4 vert and just recently bought an s5 hatch. Until i save up the money to work on the hatch, i wanted to put the exhaust on the very (it's my daily right now and the exhaust on it is torn to hell.) Are there any problems i could run into swapping this out? I know the s5 engine has a higher compression, but would that change the way the exhaust is working back on the engine?

 

The S4 uses exhaust backpressure to operate the auxiliary ports, so there's a tube on the exhaust for this. The S5 uses the air pump for the ports and lacks the port on the exhaust.

 

I know the stock n/a S4 exhaust has two pre-cats, while the stock S5 exhaust has only one pre-cat. The n/a S5 has a pipe that runs from the air pump to the main cat body - not sure about the S4 arrangement.

From what I have seen, the cat back portion of the exhaust system on both the S4 and S5 only differs in the location / position and length of the exhaust tips. The S5 tips are slightly lower / longer to the clear the restyled lower edge of the bumper cover. I had to lower the mufflers by bending the rear muffler hangers on the Borla system to better fit the S5 bumper cover cutouts and to keep the hot exhaust gases from burning the edges of the bumper cover outlets.