Trumpet filter

[Rick Parker]

The largest share of the volume of air into the stacks comes not from directly above but from the side. The OEM stacks with the non rounded edge shears the air as it is drawn into the stack. The others with a more rounded edge promote better flow. In my opinion the placement of any individual screens (such as the sanwiched foam OEM type) or the more recent production "Stainless Mesh" type which have a rubber band around the perimeter and secure themselves around the edge of the individual stack will cause a disruption of air flow at the outer edge and a resulting reduction in performance. This may only become really appearant at WOT because up to that point anything can be compensated for by further depression of the throttle, but will be felt to a minor degree throughout the operating range. Admittedly a big part of the mystic of the Webers is their no holds barred appearance, but the box type filters, such as those from TWM and others will most likely provide a better overall package because there is more filtering area and a larger "filtered plenum" from which the individual stacks pull the air. You dont see individual filters on the injector stacks on F1 cars, there is a reason.