Is it the little black box in the rubber pouch under the front plastic?

 

well i dont know about yours, but on mine that is where all the wires plug together.

 

then again, mine doesn't have a rev limiter, so never mind. i dont know anything about ex's.

 

yes that is the rev box i have a 400ex and there is no doubt in my mind i upgraded toa high rev box so trust me thats it

 

hey phaksell help me out, here is the dumbest question you will find. How can you tell a wb revbox apart from the stocker? when i bought my quad (used) the owner said he bought one, but couldnt remember if it was on or not. And I can not tell a difference, i dont see any markings seperating them apart. Help

 

1. A 250R does have a "rev box". It's your CDI, same as on the 400EX. In about the same location. It has a rev limiter, it's just not as noticeable as the 400EX.

A CDI, or Black Box, or Rev Limiter (different descriptions, same thing) is exactly as described, it's black and it's a rectangular box. It's usually located under the tank, clipped to the frame. It's not the coil, which is cylindrical and attached to the plug wire.

2. Externally, there are no differences between the White Brothers CDI and a stock 400EX CDI. The only difference you might see would be that there wouldn't be any numbers on the outside of the White Bros box. The stock box will have a three digit number and a longer number stamped in white.

 

So Pam... Besides the obvious higher rev limit with a White Brothers or XR250 CDI, are there any other differences? Do either the WB or XR250 CDI have a different timing curve? I've been considering buying a XR250 CDI if it would help with my recent 416cc upgrade, which includes an XR400 cam and FCR carb. If all it does is provide a little higher rev limit though, I might as well keep the stock unit for a little added reliability.

 

NVR2L8:

I too have a 416EX, and considered a rev box, purchased it, and returned it before I ever installed it....here's why...

GT-Thndr did some dyno tests with the WB rev limiter as did my local quad racing shop....some things I have learned:

- First, the WB rev box does NOT limit the RPMs at 10k, or 11k or even 11.5k....it keeps going. This is VERY BAD for a 400EX (with or without motor mods).
- Second, if you look at the power curves on the GT-Thndr dynos, the stock rev limited cuts in right as the power starts to seriously drop....the WB rev box obviously keeps going, but the power drops off so much, you might as well shift up at that point.
- Third, my 416EX will walk away from stock 400's, 406's, 430's, 440's (all with or without rev kits), DS650's and QR250's in 400yard drag races. As long as I keep in mind how quickly I hit the rev limit, if I shift before hitting it, or even if I hit it, I still beat these guys time and time again in drags.

The only Rev Box I will ever put on my 416EX is one that STOPS THE POWER at or below 10.5k. Anything higher than that, you are bound to damage your engine. Does anyone know of another Rev Kit for the 400EX that will keep RPMs BELOW 10.5k?

My .02

 

The White Brothers CDI is a Honda XR250 CDI, so no difference between the two.

As far as the GT Thunder dyno test goes, it's different than any other test I've seen (or even ones we've done at work). They may have gotten a defective box or something. Very strange.

The high rev CDI will typically give most engines about another 1,000 rpm. We haven't tested any that didn't shut off before 11,000 most shut off around 9,500 - 9,800.

The curve is similar to the stock box, just a bit more agressive towards the top.

What we found was that the CDI wasn't effective on bikes that didn't have a free-flowing exhaust system. My basic rule of thumb would be try all your other modifications first, if you're banging the rev limiter all the time, then install the White Brothers or XR250 CDI.

We have yet to damage a 400EX engine (with the high rev CDI) from over-rev as long as they're 440cc's and under. The 465cc and larger engines do fall apart from over-rev (with the high rev CDI, or the stock one!).

These engines really are bullet proof, even when modified. The ONLY engine failures I've seen since this quad came out were on 465cc or larger engines, or could be attributed to bad oil/low oil/no oil.

Oh, BTW, if any of you have the high rev CDI, and have problems getting the bike started, plug and unplug the box about five times. This should solve the problem (the connectors get corroded).