Building up Brother's 400EX

[00Banshee]

I am looking for you 4 stroke experts to help me out with this. My Brother's 400ex is totally stock other than a K&N filter and newly purchased WhiteBros E-Series pipe. What is the next mod you guys suggest we do before going up to a big bore? Thanks for any help and btw this is an awesome site even if I am a Banshee Guy.

[Dave400ex]

Well most People would say to get a JE 416 Piston and XR400 Cam. If he does not want to Bore his 400EX any, then he could still get a Higher Comp. Piston and a Cam.

[330EXman]

hey

on a four stroke the main concern is getting air in easy and air out fast and easy. so get an

outer wers airbox lid
Carb
K+N jet kit
High compression piston
higher lift cam. most people use an xr400 cam or you can go and get a custom cam from four stroke tech,white brithers, etc

With the cam you will need Heavy duty valve springs
A new heavy duty clutch kit with heavier springs
If possible get a port and polish job
some people favor the rev box mod, this allows the motor to rev higher. on the 400 its not so critical but like on my 300 it is. its all preference on that one

and some other thing like sprockets etc

[Matt Fisher]

The biggest "clog" to power on a 400EX is the stock cam, just like the pipes are on a Banshee.

Budget build-up: Jetting, XR400 cam, silicone for a base gasket, thin head gasket, grind out welds on head pipe, ignition advance key. You already have a filter and muffer. Possibly add disks to the e-series.

Slightly bigger budget: Add- high-compression piston or small bore job (416). You might consider a bigger cam (GT Thunder, White Bros Track cam, HRC, etc.) for more top-end, less low-end.

Makin' power: 440 or 465 with a larger cam (see above). The XR cam is too small for the bigger motors.

Options (the bigger the motor, the better these work). Headpipe for the exhaust, port work, even bigger cam (requires springs/shorter valve guides/hardfaced rockers), carb, bigger valves. There's always more...

There's only about a $150 price difference between the little bore motors and a sleeved 440. I say go big.