The pictured stacks appear to be designed for cosmetics only, not function. The sharp entry edges and no radius of the bell, the intruding flange that the screens are attached to, and the screens themselves, all will disrupt proper air flow. Those actually look like they would be more restrictive than a stock air box. I suggest you do some searches on the forum. There is a comprehensive thread on velocity stack design somewhere that delves into this subject very well.