Has anyonehere replaced the second converter on their pro? I was looking at them on a web site and noticed that these "free flowing" cats could add 3-10 hp. I know that our cars have 2 cats so I do not know if this hp gain is possible in our cars. Anybody have any insight on this topic?

 

Few newer vehicles benefit AT ALL from "free-flow" catalytic converters. Car manufacturers have figured out how to make good cats; aftermarket units usually only help late 70's and early 80's vehicles that came with older, more restrictive designs. About the only time that they will help on a newer car is if (a) the engine is modified enough that it needs a larger-diameter exhaust system and the stock cat has become a bottleneck, or (b) the car is powered by a rotary and/or turbo engine, which are more sensitive to backpressure that a n/a piston engine.