wanna know do we need to change the cat and bulit another pie to connet to the cat back system becoz the standard cat is coneted with a long pie they cannot pull out seperate!!

so my questions is :
1st how big is the standard pie which was conneted with the cat?
2nd do we need to change the cat to highflow and made another pie connet both the cat back system and the cat??
3rd to those have experience and more knowledge guys in this forum....which way u will go for....1st or 2nd???
thx!!

p.s
has any body run a honda DC5/DC2/CIVIC Type R or a 350Z(both standard )
or (both with mod) which one is faster.......
my experience ;(both modded).......i win on the start but they get me on the 3rd grar..all the way till the end of the run....
is it becoz i have a 255/35/18 rubber at the rear or is becoz their car is faster.?