A Test pipe will add alot of noise, you may lose some low end torqe too.CL9 K24a said:Your local muffler shop should have something like that. In general, catalytic coverters are catalytic converters, there aren't exactly a difference between " free-flow or high-flow". It's fairly unpleasant to say it's a marketing gimmick people try to slap on to con unwary buyers.
Catalytic converters are designed to reduced exhaust emissions and their designs are simple and identical across the board, the only difference is the size to fit different piping dimensions. If you want to reduce or completely remove emissions, fit a test pipe which will replace the catalytic converter with a straight-thru pipe. However this may be illegal in many states and countries.