If i seen a drop like that 300 rpm after peak torque, i would suspect that you had a tiny bit of detonation. Some dyno's are super sensitive to detonation because of the water valve configuration.

I will say those BSFC numbers are weird as hell, usually the engine is most efficient at peak torque, your numbers don't make any sense. Did you have any afr numbers?

Joe

Without Data, you’re just another guy with an opinion.