I have a 94 z28 and thinking of installing headers. How will it affect the performance of my car if the egr and air valves are blocked??? Most headers do not have the air and egr hook-ups. Should I find headers with the hook-ups, or install regualr header and buy a block off kit for the valves???

 

AIR and EGR have nothing to do with the "performance" of your car. AIR only runs for a couple minutes at startup, to help the cat heat up faster. That reduces HC/CO emissions on cold start. EGR is used at part throttle, generally when lugging the engine in too high a gear/low RPM, to reduce the formation of NOx. Might help reduce detonation, as a side benefit, but not a big deal. Neither system operates at WOT.

Whether you need the systems depends on what emissions regulations/inspections you have. Most headers are available in both "emissions" and non-emissions versions.