Well I installed my PC III USB and removed the flapper. I only have the Erion Racing slip on with cone removed and the stock filter and it is much better. I see most of you say only to get the PC with a full exhuast but my bike runs much better with the PC and the accelerator pump activated. Big difference on the bottom end, very smooth all the way to redline. I just thought I would share this with the others out there debating if they should get the PC with just a slip on mounted.