Mike Osucha of MORE Performance in Charlotte, NC, specializes in
   building late-model high-performance, fuel-injected engines. Since these
engines invariably are installed in vehicles with catalytic converters, his
 dyno exhaust system includes high-flow converters.  Osucha has found
that with proper calibration, an engine will make as much power with 
converters as it does without.                                                            
                                                
Dyno testing has proved that to be true.  Mike Osucha says: "We      
recently built a 396-cubic-inch LT1 engine that produced 455            
horsepower with an open exhaust system.  When we installed two     
high-flow converters, the engine produced 458 horsepower.