Hi, I've done it to my old 156 and my 159.
In both cases I bought a second hand cat to smash the middle out of so I could return it to standard if needed.
the 156 used the same cat as many jtd fiats, I used one from a stilo for about £25 and the 159 uses the same cat as a vectra, £30 verses over £100 for exactly the same part listed for a 159.
I used a large masonry drill and some steel tubing that I sharpened and then pulled the remainder out with long pliers.
The car does feel more responsive and is slightly better on fuel, and both passed the mot without issue.
A word of caution, the cats contain some nasty metals that you dont want to be breathing in so wear a mask and tie a bag around the bottom of the cat to collect the bits that come out
Last edited by JON156VELOCE; 06-03-13 at 13:12.