400ex rev box

[nstyle400ex]

hi im thinkin about gettin a rev box for my 400ex what is the best kind? and is it true that they give you more HP?

[CJM]

Dont bother it is a waste of money b/c the EX doesnt make anymore power past about 8000rpm.

If you want more power best things to do is upgrade the air filter, put on an exhaust and get your carb tuned good.

[wilkin250r]

The rev box will allow a modified motor to reach it's full potential.

If you don't have serious engine upgrades, then the engine is already AT it's full potential. A rev box won't give you anything. The stock rev box was actually designed very well for the stock motor. There's no point in upgrading the rev box without upgrading the motor.

[nstyle400ex]

my motor's just got cams? and a aftermarket exhaust and k&n filter and powerlid.

[wilkin250r]

With the camshaft upgrade, you might see a little benefit from an aftermarket CDI, but it's not going to be huge, and it will mostly be in the way upper RPMS anyways, and you probably don't spend much time at those revs.

The main issue is that the stock motor can't breath very well past 8000 rpm, it doesn't make any power in those high revs, so the stock CDI was designed to shut off there.

If you get your head ported, with oversized valves and a high-rev camshaft, THEN your engine will still make good power at those high revs. At that point, it would only make sense to get an aftermarket CDI that will let you rev higher.

Without those upgrades, and without that type of riding style where you're constantly in the upper RPM range, and aftermarket CDI is just a waste of money.

[r660guy]

we have two 400exs and one is bored out a couple millimeters, the other is stock. they both have hi flow end caps and procom rev boxes. with the rev box it made it quicker on the top end and improved the throttle response. i also have a big gun rev box on my raptor. i love it.

[nstyle400ex]

alright thanks guys.