Hey guys I am positive I am going to get either a 426 or a 440 bore kit for my 400ex along with a cam shaft prob stage 2. As I dont race or anything I just ride the trails hard I am just looking for a little more power on top of the jets and full exhaust system I have. Now with one of these bore kits how does the cooling work will the stock oil cooler work with the bore kit or are there other modifications that you have to make to the cooling system? thanks guys

 

Try to not excede 10.5 to 1 on the compression, as the head bolts are the weak link. Lots of guys use the heavy duty head studs when doing the upgrade, to prevent blown head gaskets later on.
Cooling also becomes an issue, at the higher compression levels, but as long as air is flowing past the motor, it shouldnt be an issue, but you definetly dont want to do much idleing, once the motor is up to temp, and watch out when you get stuck in mud, and do alot of wheel spinning, as overheating will happen fast.

 

Thanks for the info, So wiseco only makes an 11:1 compression piston for the 440 kit so what your saying is I should get heavy duty head studs. If so do you know where I can find them?

 

Heres one sourse
http://www.gtthunder.com/TRX400EX.htm