Originally Posted by
Grinder
The 11.5, and 11.9 cranks are both fast. I think Novarossi went with a larger crank so they could try to make more power. It seems like Novarossi felt like they hit a wall with the 11.5mm crank design. The larger diameter gives them more options as far as bore size to play with. They can flow more fuel through the larger bore. To make the bore that big on the 11.5mm crank would make the crank too weak.
A big bore is also possible with the 11.5mm crank but you do need more expensive materials and an advanced (time spending) hardening proces to get it right. Larger diameters will give more strength by itself preventing extra costs in production. Also with larger messurements you can keep the same tolerances or even lower them for a faster production.
Looking at MAX and GiMar their toplevel engines do come with both crankshafts so it seems possible with the "old" smaller diameter.