Yes, thanks to Japanese, the video I could see confirms it's possible to manage a long-boost at the level of the jump !

I don't know if everybody know how build a long-boost ! I try to explain :

_ just when you arrive on a turbo arrow, stop to push B and start to push left button, and just after push R to do a little jump for hitting the wall (it's important to press a direction when you hit the wall, I think the long-boost is longer when you hit the wall by the kart's side)

_ then push right button to move in correct direction, and cut all the sand without push B



I think it's possible to do a 13"5x with a solid experience !

Yes, because if you only press left, ........... you go so in left direction that I think you always miss the lap !