Mmmmmm... let me think, my first mod was OMP strut braces (front and rear) which I ordered soon after I ordered my 172, and the strut braces arrived before I got my car! I akso ordered a OMP steering wheel but its still sitting under my desk, but thats another story..
About the OMP exhaust, itis a stainless steel 2" system with single round tail pipe (& decat). I have seen and heard one fitted to a 172 and it is LOUD! I would say at least 40% louder than my Magnex system.