In recent yearsat the TT, only the Norton, the MV and the Moto 2 bikes had open exhausts. I would have thought if there was any power advantage to be had by having open exhausts where there are no restrictions, they would all be doing it?
There is also the question of rider fatigue, even with ear plugs to take into account.
To keep this on topic,If it were possible, I would like to see ( hear ) open pipes on race bikes at the TT as a change for next year.