if you (like i was) were unfortunate enough to own a mk3 8v having a decat is necessary to get any kind of power out of that engine!
I think a de cat just makes it lighter 
I just fitted mine, I did weight it actually

lol. Umm, original de cat was nearly 7kg and original pipe with cat hollowed out was just over 3kg...4kg could make all the difference

Was a real pain in the arse to fit, did on my drive on axel stands. TIP - Wear goggles, I got loads of soot in my eyes
