Factory exhaust pipe size ?

[Initial_Z]

I have a 90 TT. I'm planning to do an exhaust cutout before the Cat. I might be ordering one of these:

http://cgi.ebay.com/ebaymotors...fcd98

They come in 2 different sizes:

Total Length 11" Piping ID 3" Piping OD 3 " Height (cross diameter) " 3 3/4" at motor Width 7 1/8" or 8 3/4" total with motor

Total Length 11" Piping ID 2 1/3" Piping OD 2 1/2 " Height (cross diameter) 2 1/2" 3 3/4" at motor Width 6 1/8" or 8" total with motor

Which one should I get if I want to place it before the Cat ? Any general thought on the product is also welcome.

Bach,