As impressive as the ZL1 was in its day, actual engine dyno tests of a certified production line stock ZL1 revealed SAE net with output swelling to SAE gross with the help of optimal carb and ignition tuning, open long tube racing headers, and with no power-sapping engine accessories or air cleaner in place. A second engine dyno test conducted on a second production line stock (but recently rebuilt and partially blueprinted) ZL1 revealed nearly identical figures for the various "gross" conditions.