Im thinking to put a 415 bore kit in my 400ex my mechanic say this kit will give me A good
boost in overall power, and provides approximately a 20% increase over stock horsepower. Cylinder
boring required (no re-sleeving).
He says all I need is a 415 bore kit $235 and an high rev CDI $117
is this al a really need or does it need more

2001 400ex
fmf megamax 2
nerfbars
twistthrottle
k&n air filter
renthal handlebars

 

While you have the head off go ahead and drop in a XR400 cam. You can pick one up for about $130-160. A little porting wouldn't hurt either.