At speeds from say 80 upwards how significant is the drag from having the top down? My friend in a Z pulled on me more then I would have liked (on a closed course obviously ) and I was wondering how big of a factor having the top down was. I'm thinkin it has a much bigger effect than I previously thought...

 

it has been discussed before and proved that

top down S2k is slower than s2k with top up

 

And over 100 is probably where your friend has the advantage anyways...