You can get a good idea of the efficiency of the airbox by connecting a vacuum gauge to the port where the air injector gets its air. This will give you an accurate picture of the average pressure drop across the filter and inlet port. Next, move the guage to one of the vac ports on the manifolds (or use second gauge), run the bike WFO under load and you will see the pressure drop across the carbs and the outlet paths of the airbox.
