hmmm, I guess Ill get my Mechanic to do some logs with me, would slip on the RR cause this symptom?
Could be a number of things / combination of things. A good logging session on the road and dyno will help pin point whats going on.
1) I get graphs like this when my back straps are not tight enough and the tyres lose contact with the rear roller drum of the dyno????
2)It the map and its running an agressive N75 pilot map which causes the boost to over shoot the target load the cut back quite hard, and not ramp up to the requested boost line, (its not a bad map just a method used by some tuners to get the boost in strong and early) On the road this mapping method would see 2/3psi overshoot and the spike/dip would not be felt.
3) Rolling road dyno acceleration rates. If tested on a dyno with little load or a fast acceleration rate then the due to the map characteristics of the N75 Pilot map (used for spooling) then it can induce a much bigger spike. Run it on a dyno with very slow acceleration rate then the peak would be much less.
IMO all that count is that your happy with how the car feels, IMO rolling roads should be used as tools.