in the for what its worth,, on back pressure adding ANYTHING at any time just means your tune is not right, does NOT matter if super , Turbo , NA , Stock, Modded . It might mean your cam is all wrong but then thats another subject alltogether.
Care to elaborate?? It's been shown by Magnaflow and Flowmaster both that the performance drop from using their cats is negligible.. They were designed for lower emissions while not increasing backpressure. I plan on using a couple of 2 1/2 Flowmaster cats on mine when I'm able to go through the exaust on it so I can pass the visual part of the inspection here in Va..