Luka87 said..
i am using stock fin c3 venom 48 with my ncx pro 8.0, also using caas mast 490, which is made specifically for this sail. Both ncx pro and turbo are 2013 so mast curve should be the same.
++ bigger fin. Try some bigger 50cm+ fins. Not sure what the max for 131 is however its an easy experiment
What size fin was your friend using with the 9.2?
cheers Jeff