These are new headers never been installed will not come in original packaging. Here is the info from the manufacturer.

This is the single most significant power modification for a non-turbo Z car (short of nitrous). Expect an increase in horsepower throughout the RPM range with the greatest gains at higher RPMs. The car remains driveable and noise level is not increased. Features Mandrel bends, T-304 stainless steel, Dyno tested design. Benefits: Optimum flow characteristics, long life and excellent heat dissipation, expect up to 12-16 rear wheel horsepower.