Alright, I'm needing a new exhaust setup for my '89 Vert, but can't afford any of the online manufacturer's at the moment, so I'm looking at nailing the exhaust off a local car. Problem is, I can't remember for the life of me whether or not the S4 NA exhaust is compatible with the S5, since I do remember the S4 5/6 ports running of exhaust pressure versus the S5's not doing so. Any help here would be appreciated.

 

You can use an S4 stock exhaust system on an S5 just peachy, aftermarket S4 units would require a plug or cap if it has an aux port bung.

 

Cat backs are the same, except for verts tend to have more baffels (sound deading) in the mufflers, and Turbos have the least amount of baffels in the muffler.

Cat forwards however are vert only and series specfic