Spend the money get you self a GrayDon.My bubby has one on his 400ex and he beat all other 400ex with other pipes.He had full big gun an a slip on fmf both junk.Get a GrayDon K&N JET kit jet your carb at 165 set your need.

 

...Hi,Just spend the $ and get a Sparks x6,do it right the frist time.And if you really dont want to spend that much then get a WB,but its not that much chepper $30 i think??,but get a full system it will make a differents..Thanks

 

I didnt notice much difference with just pipes and air filter. Get a cam. You may be letting more air be able to flow throught the motor but your valves are still restricting. Its not a 2 stroke.

 

I have the Duncan FatBoy4 complete pipe and I notice a considerable difference. It was expensive but I beat my buddy who has a WB slip on. I would suggest that you get a K&N air filter and rejet with the new pipe. If I had the money I would also get the Edelbrock and not worry about rejetting all the time. JMOP.

 

I found the edelbrock pretty good. I haven really tinkered too much with it. Its basically like it came to me. You will bearly feel 1 hp increase that you will get from pipes and filter alone. Get the cam!!! Then your pipes will howl!