there's at least 8 without using bsb

boost-br into the lap, boost-br at the first pad, hit the peak of the slope for another, br at the cut in the tunnel, br from raised track to the left of the straight before the next tunnel, br down the next cut, br off the lower hill's plateau, which can net you enough speed/air to get another one.

I haven't done this track in a while on rapier so I may be a little off