it comes down to the driver. the kfx, z and dvx only go bout 2 mph faster and only have about 2more hp than a 400ex. Dirtwheelsmag is always saying the 400ex is no chalinge for the uther 400s cuz the uthers have a 2 hp advantage. Dirtwheels is good at lieing. u could take a 400ex against a yfz and still win on the 400ex cuz it depends how good u r. only advantige the z has is drag racing witch is the lamest racing u can do. and a extra 2 hp u cant even feal. if u stuck doug gust on a moded 400ex like hes z400 he would still probly come in the top 3.

400ex makes good low end power the higher rpm u go u start loosing power on the 400ex. that is y its useless to buy a rev limiter for a 400ex at less the people with them dont no how to shift or want to get 1 mph faster.if u r going to race jest gear it down so u have alot of low end power

i have a 400ex with mods for sale in the clasified spot.

its close to the top of the page

still would like to see a better looking and better taken care of 400ex than mine

 

You typed the words right out of my mouth. Some people are saying only 2 more hp, only 1mph faster yada yada. My brother has an ex, and even if it were same top speed the z gets there quicker. Plus the suspension is WAY better. I'm not bashing Honda, the ex is a great machine. Get the Z, I think you'll be happier.

 

the Z is a little faster than the ex
but any quad can beat anyother quad depending on how its set up
and how good the rider is. I've beaten many of quads and lost the same
im not in it for who I can beat or how fast I can go, I just love to ride
and not think of anything but having a good ride

 

well i have a 400ex and the engine only has a k&n filter no air box, dyno jet kit, white broe-e-series slip on moded in the core for power and so it revs faster and its turnt in to a shorty, and i have 18" tires and win in a drag race agenst r rapter that has k&n air box cover, uni filter, the spark arrestor took out and jetted. theirs nothing rong with r rapter eather!

rapters r more power full than the z kfx dvx and 400ex but i still win in drags and i win on a short track oval race and smoke em on mx type tracks.

so whats up with that

 

I have a 2003 Z400 and I raced (stock Z at the time) against my brother-in-laws 400ex with a slip on pipe. We raced several times, then switched bikes and raced several times again. The Z400 won EVERY time regardless of the rider and regardless of who got off the line a little quicker. This was at Coral Pinks on a flat going about 150 yards with the Z always 1-3 bike lengths ahead. With more room the Z would continue to widen the gap. I know rider ability comes into play, but once your moving and the throttle is pinned, it's all bike. That being said, the best bang for the buck for a sport bike IMO is a used 400ex if you don't have a lot of money to spend. If you are a decent rider and trail riding or zipping around the dunes you shouldn't have too much problem keeping up with the other 400cc+ machines. In stock form, my wife prefers the 400ex to our Z in the dunes due to the low end grunt of the ex and the fact that the Z likes to be wound up. Once I piped/jetted the Z it's no contest, the Z now has tons of low end, mid etc.