Can i confuse matters here......
.....well, when I went into get my centre section replaced the garage had kindly ordered up the whole exhaust system just incase anything else needed replaced. The CAT section had two muckle CATs side by side, like a divers air tanks, they were HUGE!! I looked under my car when it was on the ramps and I had a one single small CAT. I asked the techy and he said it was the dual CAT was standard for 172s now??
I have sinced checked with three other MK2 owners(2 CUPS) and all have had the single CAT?
Hmmmm, could this explain things..........