Of course it is legal to cut the resonator off of the box. You dont even have to use the stock box, its ahead of the air/fuel meter and therefore what you do with it is FREE, as long as the air is coming from the stock location or from inside the engine compartment. If you were not allowed to remove the factory box and/or cut the resonator off, every single car that won the ARRC last year would have been disqualified.