Not exactly anything. GM has squeezed every last bit out of these cars. Not much more to gain. Replace every replaceable panel in cf, couple pounds off...add cam, headers, intake?, 70 HP, save 40lbs...take out interior, done already. Brakes, done Already...wheels, cf, small accell gain. All this and we have not improved the car much. These cars are maxed out. Zl1 needs grip, really needs grip, that's why the big gripe about the tire issue in the 3 second comparison. All that carbon brake is not gonna stop the car without tires that can handle1.5 g deceleration. Zl1 brake are exemplary - just under exotic, but they need more gummy rubber. So no brake change, no big dollar mods, just put the trofeos on a zl1 and run it at the same track, then tell the camaro customers that you want to charge them more money for a Camaro that has less standard comfort , but is only .5 seconds faster than the zl1...they couldn't market that....hense the slicks.
Answer this and and a sensible person would stop asking why anyone wants to compare the Z camaros with the same tires:
a z06 with those pirelli trofeo tires will best a zr1 on Goodyear f1 supercar tires.
Wouldn't it be absurd if gm sold them that way and marketed the z06 as the top tier car?
No one trying to justify a zl1 purchase, drive one and you'll be very aware that was never the case. Those who have powerful camaros understand the traction issue, I guess those that do not have, do not understand.