XXX-S motor clamp will not work on the XX-4. There are a few trinity XX-4 motor clamps floating around, but they are tough to come by. I believe someone in the For Sale thread was making aluminum ones, but I can't remember who. Maybe someone else has the info. There are not a lot of hopups out for the XX-4 anymore, but Penguin RC makes great carbon fiber shock tower braces, a must for the racer in my opinion. I break far less often now that I have them. Good luck in your search.