Good home required for two cats... well on a serious note I can now report what it is like to have a decat pipe fitted to a 172. Many thanks go out to my mate who did all the physical work such as welding, fitting, etc.
If anyone is interested then I can produce a "How to fit a decat pipe to a 172" in the Modifications - Exterior, Power & Mechanical area.
The car seems to have a bit more pulling power when you floor it on cam. There is an induction like noise between 2000 and 3000 rpm but its coming from the decat pipe. Cruising along there is very very little extra noise over what I had before.
In general on full throttle you definately notice a louder exhaust noise and it sounds good if you like this sort of thing.
Also the famous banging noise that many 172 owners have had has magically gone !!
The cats themselves weight quite a bit more than the decat pipe so the car is a bit lighter as well ! Also looking at the cats you notice that there are several places where the piping is very narrow indeed - I would say flow restrictive.