Dunno if I posted this in the right spot, but looking to buy a used 26-28foot cat. Nada only goes up to 500hp on engine option. How do you know how much value to add for a 525, or ilmor v10 625hp etc..?

Look in the classifieds for comparisons. Nor Tech put ilmors' in some of their boats/cats and the 525 was a standard upgrade on many hulls. Remember insurance cost
. There is a forum on here for that also. Good luck on your hunt.

NADA is pretty worthless for actual boat pricing/values. It is what banks use to protect themselves.