How much will a CDI help my 400.

 

Unless you change Cams it won't help at all. The Cams in the 400Ex quit making power at a certain point to rev it over that you are going to just be reving the motor.

CHange the cams to ones that make power up in the higher RPM range and than you will need to change the CDI to have the spark continue though the RPM Range.

Smitty

 

one of my friends told me to put in a xr400 cam and 11:1 piston

 

the best hop up for a 400 ex!!!!!!...put a z400 motor in it.

 

Yeah...Suzuki did it, why can't you?!