Any body have any good guesses??Me and my buddy both have 400ex's his is a 99 mine a 2000 we lined them up on black top several times an his keeps beeting mine 4-5 quad lenths and yes we switched drivers to see if that was the problem.They were closer 1 quad lenght.But his was still faster. I out weigh him by 35 lbs.Both quads have the same dyno jet kit,and the same white bros.rev box,stock gearing his has a white bros.E-series slip on.Mine has a pro circuit head pipe and a white bros R-4 silencer.We were thinking that maybe the over sized head pipe was hurting the bottom end torqe ??any ideas??Top end speed seems to be about the same.I'm modding the motor as soon as all parts arrive.11 to 1 piston stock bore. Hotcams stage 1 and Edelbrock quicksilver. We just lined them up for base line to see how much difference the mods will make.Is the E-series a better silencer.I was thinking about going to one anyway (alot quieter).Do you think these mods will work well together.I plan on ice racing it this winter and would like to beat him bad.But still be able to have a good reliable trail machine. Any imput is appretiated.Thanks.