If you want to buy some mods. I have a White Bros.E-series pipe, K & N filter, bigger main jet, White Bros. Rev box, Tag X5 quad bend bars, Graydon Proline nerfs, White Bros. E-Z Pull clutch, PRM baja front bumper, & a DG baja rear skid plate. Hardly used. All for $600.00 e-mail if interested.

 

First of all, make sure your throttle is adjusted. You can gain a ton of performance (esp on top) by doing this, as nearly all 400EX's are set incorrecly from the dealer.

Once that is taken care of - if you want/need more power then it will be time to decide how big a bore you're comfortable with. If you don't want to run race gas or a race gas mix, then about 11:1 is the limit on compression. Get a fairly aggressive cam. The GT Thunder cam is an excellent example and you won't have to get "hardened" rockers.

The other critical element to making a fast 400 is the carb. I'd recommend the Keihin FCR, it's expensive, but worth it. A much better dollar/go fast ratio than a pipe for about the same price.

With around 11:1 (regardless of bore size), an aggressive cam, FCR carb, a little port matching, and a fairly free flowing exhaust (aftermarket or modified stock), you should be able to outrun piped Raptors with ease and even some modified Banshee's & 250R's.

Building power on the 400 is all about a complimenting series of smart modifications.