Buddy of mine has a 400 eiger and is looking into an aftermarket exhaust. What would you guys recommend and does someone make an aftermarket clutch kit to compensate for the extra power? And what are some other possibilites for other mods?

 

HMF Utility Series pipe (get the 'Quiet-core' insert or it WILL be too loud) as well as a UNI air filter and rejet the carb up one or two sizes. Do it all at the same time. The power increase will be noticeable but not huge. The clutch will not need to be upgraded unless you go with significantly bigger tires, which is not really a good idea for a 400 anyway.
Any more than that will involve a hotter cam or higher compression piston, but these will really require some mechanical skill to do

 

Is this the most common upgrade for the eiger? And Does anyone have experience with the HMF pipes on the eiger? I have an HMF on my Arctic Cat, and HAD on on my quadsport and they performed well.