BT stands for Black line Tunnel, a tunnel inlet made of PU-foam. De BT-01 has a flange of 40 mm around. Leaving upper or bottom flanges aside, the inlets can be mounted on top of each other. Synchronisation of the inlets is easy with the fine tune screw. The BT series can be self opening or self closing.
The self closing version has the big advantage of being completely closed even if the inlets are not synchronised. The force needed to open 5 inlets on top of each other is only 16 kg, only 3,2 kg per inlet. Aerodynamic design gives the BT series 8% more air flow.