I have a 400ex and I want some more top end speed, I dont wanna change the gearing cuz i will lose acceleration but i ride with raptors and dirtbikes and i just get left behind. Please help, i am considering a 440 kit, but will that really help?

 

Get them on some tighter trails, then you'd whoop on em. Well, prolly not the dirtbikes, but maybe the raptors.

Looks by your signature you already go some of the common mods...exhaust, and jets. Might also go with a different air filter if that's still stock. With that you might need to jet again but it might get you a couple MPH. Then if you're not want to do a gearing change or engine mods, might look at bigger tires. Going to a 22" tire might give you a MPH or 2 also. Gonna cost ya some low end though too. Could also put in a different rev box and get a bit higher RPM also. After that though you probably looking at engine work...

 

What kind of engine work would I need?

 

Stuff like you mentioned. A big bore kit, porting, cams, and pistons. Stuff like that. I don't know what allot of folks do to the Hondas though, but I'd assume it's the same type stuff that can be done to any of the 4 strokes.