Mark Stielow is a perfectionist so they're probably still tweaking things. Since they have a ZL1 and C6 vette going around with the Z/28 my guess is they're studying what the computer is doing with the shocks on the ZL1 and C6 and developing "ideal" settings for the custom shocks the Z/28 has.
They're going to have to have a final "this is ready for production" setting for everything including engine power before they can give an official lap time. The fact they've been working on this car for 2 years and still haven't given "official" numbers is a good thing; that means Stielow and team are still making improvements.
