I'm looking to put an exhaust on my 400ex. Is a full exhaust with headers going to make a big difference over just a slip-on muffler? I plan on keeping the motor stock, with exception to the pipe, air filter, and jetting. I read that the header will only really help if you have done some motor work. Is it worth the extra $200 or more??

 

On a 400EX it's not worth it in your case. You may see the slightest power increase but not much with a stock motor.