Yes the reason the dyno chart is like that is because of wheel spin on the dyno.
We had a few attempts at it. With a couple of guys in the back and 4 x 20lt water drums, plus it was strapped down.
And just in case any one asks, "1st Place" S13 Silvia and "1st place" R33 Skyline were both run in 4th gear, not whats printed on the dyno sheet (3rd).