how much of a power gain can i get if i were to remove the airbox lid and rejet accordingly?

 

as your letting more air in, you should probably make it easier to go out too.

an exhaust and k&n filter (no airbox lid) is all engine stuff ive done to mine and it felt like a different bike afterwards.


but to answer your question you may notice a difference but it would be much more worth it to get an exhaust and rejet for that too.

 

to tell you the truth whiteflash the power gain would be minimal, but u would be able to feel the accel hit alittle harder... with the exhaust you add more tourq also... i would go ahead and try that

 

Nice alternative to a wide open airbox! (http://www.ehsracing.com/)

Venting the lid, will help, but you will be better off if you also get a muffler and different air filter. I prefer foam air filters to the K&N, and like the UNI air filter for the 400EX.