Another dump valve thread
 

I have a bailey twin piston dump valve which I had fitted to another car, I have a 95 uk classic. Im still reading up on the scoob so Im not sure on its suitability. How does my scoob meter air, is it by an air flow meter or a map sensor?

It meters air/fuel by MAF (airflow) sensor.

So yes, what your thinking is what is expelled by a vent-to-air dump valve is affecting its operation. Only momentary, but sometimes enough to cause the odd pop out the exhaust and hesitation between gearchanges.

The MAP sensor is just used to regulate boost pressure, nothing else.