I picked up a 2000 WR400F I ride only woods, no track. I'm planning on doing the free mods to include changing the timing w/ gray wire, timing chain, throttle stopper and air box. I'm looking to get this pipe from Rocky Mountain: Yoshimura : Comp Series Full System, Yamaha My question is do I get the WR pipe or the YZ??? They have different part #'s both have spark arrestors. If I'm running YZ timing it would make sense that I would want the YZ pipe?