As HCI2000SS points out, there was a similar thread on this subject a while back.
https://www.camaro6.com/forums/showt...light=diffuser
If you're tracking your ZL1 and trying to eke out every ounce of performance, having a big gap underneath the car in front of the rear diffuser could have some effect on lap times. The effect of that same gap on the street is probably negligible.