I have now seen several references from Twin-shocker regarding airbox mods to vintage bikes. Up front, I want to share that I have followed and applied airbox resonance and tuning on other vehicles, but never on a trials bike. In general, on high performance engines, airbox design can be critical. Typically though, and for the sake of discussion, the airbox inlets must already have adequate airflow capacity to handle the engines size. A tuned airbox resonance is more important on engines turning higher rpm and within a narrower rpm range. Bikes such as a road race machine or small bore mx bike, personal watercraft and sleds tend to fit this criteria well. Granted the last few years have seen improved airboots produced for the 450 mx bikes also. Vintage trials bikes, in my opinion tend to be ridden at low rpm and minimal throttle, with the added function of the throttle is not held steady nor in one position for any duration. I do believe that airbox volume in the still air portion is important to lessen engine acceleration issues from inadequate immediate airflow across the filter. Books written on the subject indicate suggested airbox volumes needed. Resonant tuning a two stroke, and even the four strokes brings the discussion of fuel stand off in the carb air inlet bell and extending even some short distance up the airboot. Fuel stand off is a function of resonance. The engine pulses generate a reverse wave through the carb and since not all fuel is consumed on each intake function, the resonant wave tends to carry atomized fuel back to the waves break point. The break point is a function of throttle opening, engine intake timing, and the mass of the air being moved. On a steady throttle operation, such as the examples posted earlier, a known setup can be made and tested to optimize resonance and fuel stand off. At low throttle settings, and changing throttle settings, resonance seems less important. I do consider the rubber airboot between the carb inlet airbell and the airbox important. Not in a sense to gain a resonance performance gain, but rather to minimize premix spray into the still airbox. Maybe if vintage trials bikes were doing those wide open moves we see the modern bikes accomplishing then possibly some airbox improvements may be a benefit. But overall, it seems most vintage bikes are not revved high nor for very long. Curious what others will offer. No doubt good comments, wise cracks and general foolishness, but that's ok too.