Na, the 80% days are the "Fun Days" usually run on a sunday. The cost for the fun days is $30 or $50.
I have done a couple years ago when not too many turned up for them, but lately, hundreds turn up. too crazy for me.

Friday sessions are more for suspension/chassis setup. You never realy know what sorts of cars will be there, often a couple of HQ`s, commodore cup cars, formula ford and V`s, Improved production cars. maybe a GT3 or V8 fujitsu car.
You just have to keep an eye on the rear vision mirror for the faster cars comming up on you and give them room.