First off just to give some background info. I'm planning on getting the K&N Power kit(with jets, filter, etc.) and a White Bros. E-series pipe(not sure if i'm gonna get the header pipe or leave the stock one? All will be installed at the same time). Is the K&N Filter with Prefilter good enough intake?? Or should I leave the airbox lid off?? Is leaving the lid off safe?? Has anyone done this before and does it make a difference?? Is there any thing better to do with the airbox, besides removing it all together? The above mods are all I plan on doing(except for maybe a rev box later on). Is it necessary to replace the stock header pipe when doing these mods?? Will it make any difference what so ever??? Keep in mind, I don't mind spending the money on one if it will help even just a little bit. I"m looking for mostly low end and mid range power. I mainly ride in trails and rarely get into 4th and 5th gears. Once again, you guys are great and thanks for any help or input you can give me. I also posted this question on www.exriders.com forum. I want to get the most feedback possible. thanks

 

Running the air box lid off won't hurt anything as long as you have the sock cover that goes over the airfilter. In fact it pulls so much air that you have to run with it off. Im not sure about the head pipe. Im pretty sure it would work. The E-series has little disks on the end so you can add or remove them to add top or bottom end (depending on the riding conditions). But it sounds like your getting that bike ready to rock and roll. Have fun. R.R.

 

I would recommend maybe changing the gearign for low end.
I would not get a header pipe as i have heard the stock flows very well.
I would probaly go wiht a 416 or 440 kit because there is no replacement for displacment

 

Holty, as long as you purchase an "Outerwear" when you buy your filter, running your 400EX with the airbox lid off is not only good, but its normal.

Your stock Honda header pipe will be fine for that silencer. Honda has a high flow head pipe, and a muffling exhaust. Replace that silencer, and you'll be in good shape.

I recommend dropping down a tooth on your front sprocket, and that will give you more low end. If you have 20" tires or taller, you COULD drop down 2, and have gobs of power down low.

 

thanks for the help!! I will take your advice and run with no lid.