Rev box for Duncan 440 national

[rob-u/21]

I have full Duncan 440 national kit on my ex. I am using the stock revbox. Will I get better performance if I go with an aftermarket box. Also will I hurt the engine in anyway. One last thing, which rev box will give me the best performance.

[JRDrider22]

i got white brothers..works great

[rob-u/21]

any other suggestions.

[Yamahauler_04]

No. THe motor was designed to work in the stock rev range. Spinning the motor to high RPM's is not what the kit was designed to do. It is designed to compliment the stock 400ex characteristics, not change them.

[bpimpdaddy21]

Yes, call up GT Thunder and get there rev box, seems to be the best one I have read of so far. You should notice the difference.

[Big - D Racing]

I run their kit with a dyna ignition. It raises the rev limiter 400 rpm's, which is truely all you need for a built 400ex, the white brothers and most cdi's are overkill because your bike starts dropping off in hp around 8000 rpm so that is where you ideally would want to shift not at 10,200 rpm. Plus white brothers and many others on the market are just an xr250 box that makes your bike hard to start, dyna doesn't do that.