The main difference between the two carbs is the Thunder has a AVS style top cover. The secondary side is now tuneable via a locking spring on the side.
Since it is tuneable, IMO, you can end up seeing more torque as well as not getting that famous "dead spot" when you suddenly wack the GO pedal. The counter weighted air door of the AFB suddenly opens creating a lean moment.
I personaly do not see a difference that would leave me to believe there is a CFM difference.
