Originally Posted by jeffreylin

It's their newest and it's more like a Plus 21-3. It has a bigger bearing (14.5mm) than the 321P (14mm) and it's a 9 port vs. 8 port for the 321. It's what they used at the worlds. Harder to tune but with great mid range and top end.

For details:

http://novarossi.it/eng/motori/35plus21.htm