I had a silvia with full apexi system in it and it had a throttle body like assembly on the pipe work befor back box, it was a manual type and a cable like a throttle cable was used to open and close it, only problem was you cant drive them on even a small bit with the flap closed, no power and exhaust gasses start to push there way back other way, id swear at one stage the were cumn back through airfilter, wouldnt think it be too good for engine and i wouldnt think it will pass nct due to emissions