How restrictive are they compared to off-road H-pipe and stock. If Off-road is a 10 and stock is a 1.. where would the Hiflow cats fall? Also how about noise? I am sure they are more quiet than Off-road, but how close to stock for sound are they.
It's actually pretty close as far as HP (Stock engine), until you do engine upgrades such as H/C/I or blower/turbo, then the offroad is way more beneficial. The biggest benefit I see on a stock or mildly built car is sound (much louder).
I had an off-road h and had to weld in two high flow cats to pass emmisions and i hate it, cut the sound by allmost 50% but its still louder than stock