yea i bought a 400ex. it came with a DG pipe. i was wondering what i could do to make it faster and cooler for cheep... idk what i should do.

 

Is it currently properly jetted for that muffler???

Opening up the airbox will help (unless you run in the wet), as would a header, but that will require another rejet. I would run the FMF PowerBomb and Q4 (I currently have the PowerCore 4), the ProDesign (ProFlow) adapter and foam air filter, and EHS Racing airbox lid with Outerwears.

I don't really think it's worth doing a cam and/or different carb, and certainly not boring it out.

 

Its not worth doing headers either unless you have major head porting and polished due to the size of the stock one which is more than enough for stock motor!!!