I'm after your thoughts on choice of cats for the L98 (6.0L) going into my Harrison. A sponsor on the LS1 forum has a sale on cats suitable for my car (4" body) and I have an opportunity to buy the pair for less than $500.
The question is what size inlet/outlet pipe diameter should I order for the cats? If my steering clears the VE Commodore factory headers that come with the L98 crate engine, then I'll present the car for rego with those in order to keep the noise down. If not, I'll be going with Harrison's custom headers which are a 4-into-1 design that presumably end in 3" pipe and I'll probably fit them later anyway (just for race days).
The cats are available in both 2.5", 3" and 4" inlet/outlet and can be ordered with different sizes on each side. They're 100cpsi meaning the cells are 4 times the size of standard ceramic cats and twice the size of stainless substrate cats. So they will flow nicely!
Since I don't plan on any more than 300kW, I'm thinking 3" inlet to match the custom headers and 2.5" outlet into a twin 2.5" system (possibly even more restricted for rego).
Or would it be better to go 3" outlet because I can always restrict down to 2.5" but still be able to go back up to 3" if I wanted to later?
I'm planning on cosmetic sidepipes and an underbody system exiting to the rear for rego, and for "race days" they might be shortened and directed out behind the sidepipes as I have seen on a number of cars.
Thanks in advance.
Paul