Help needed with odd dyno results (2.5l time trial car)

[911monty]

Well I'm no expert but since no one else has chimed in let me be the first then someone may come on to correct me!! If the AFR is even close then it's too bad you do not have the ignition curve on that plot. From a casual view, if the AFR is that lean then detonation could be causing the timing to retard which could cause some of that 50 HP loss. It might be interesting to see a run with no MAF and base map.