I recently completed some air flow analysis on my 2003 WR250F and found marked improvement with the Twin Air Power Flow kit over stock. I also found little difference in performance with the entire side cover removed and is certainly not a worth the risk of water intrution. If you want more performance with the least amount of risk I would defiantly recommend the Twin Air Power Flow kit. I just changed to a larger pilot jet this weekend to compensate. If you would like to review the results of my testing and some pictures. I have removed the link to avoid any ethical debate. If you are interested in my results - pm me. Enjoy.