Rev box question

[Jgrimm400ex]

I have a 400ex and w/ WB e series k and n filter jet kit. I want to get a wiesco 11:1 piston and a hotcam stage 2. I read on a thread that it will run all the way to the rev limiter. If so do i need to get a better one and wich one? Do i hurt the reluability?
Need Help pleaz.
PS i have the supsension part comin.:)

[honda400exrider]

umm im pretty sure all of the rev boxes are pretty much the same

[F-16Guy]

pretty much all ignition boxes raise the rev limiter about 1000rpm. The main diffference is the advance curve. Some boxes retain the stock curve, and some make the curve more aggressive, advancing the timing earlier in the rpm range and increasing total advance.

[KAWSAM62]

the diff curve is what your after not necesarily the extra rpms the timing curve makes it pull harder in any gear xr 250 box is what i use:devil

[DGR Designs]

ive got a white bros one. my old man won't let me have it lol he thinkins ima drop a valve lmao! do they advance the acceleration any?

[F-16Guy]

I heard some rumors that the WB rev box is the same as the xr250 box. I did notice that my WB box is quite a bit smaller than the stocker. Does anyone have some first hand knowlege on this?

[JustRace]

Don't waste the money on aftermarket rev limiter. There are a couple dyno runs that show no added power, and they make cold starting harder. Also a your 4-wheeler is already past its peak power at the stock rev limiter there is no sence in over revving it another 1000 rpm's because you will not gain anything.

[F-16Guy]

Too late, I already wasted the money. BTW, I've never had a starting problem w/ my WB box. I think 99% of the starting problems are jetting related, or a faulty helmet-to-seat adapter.

[gojk]

Actually I have one, and if my battery isn't fully charged it will not start with out a push.

[GetHigh250r]

i heard they do lower reliability too, because your working your motor to hard. It made to run how honda sets its, leave the box stock

[gojk]

If you have a built motor that has a CAM that puts your power higher in the RPMs then I recommend it, but other than that it isn't that much of an improvement.

[Steve-o 400EX]

From what a mechanic told me at my local dealer, the rev box's do make it hard to start in the winter when the engine gets really cold, he told me to use the stock box to start it and then when gets warm, shut it down and put the performance one back on, he said its good for the avdvanced sparking and not good for the extra 1000 rpm.

[mod300ex]

how do they modify it ne ways?

[Steve-o 400EX]

It is just a little box that plugs in where your old one does, it takes all of 10 seconds to change.

[86atc250r]

Here's the deal with "aftermarket" rev boxes (CDI boxes, etc)...

Almost all (except MSD and maybe a couple others) are really an XR250 CDI box that has the company's sticker on it. This box is easy to identify because it is physically smaller than the 400EX box.

The XR250 box does not alter the timing curve (despite what those marketing these CDI boxes would have you believe). The XR250 box also doesn't provide just 1000 more RPM, if it does have a limit, it's far beyond what the 400EX will turn without self destruction. I've seen 400EX's spin in the neighborhood of 12,000 RPM with the XR box - stock is 9200 RPM.

They will not start if the engine doesn't spin over a certain RPM when cranking, this is because of the "Anti kickback" circuit in the XR250 box.

A higher rev-limit does put you at a much higher risk of "throwing the connecting rod" in a 400EX, especially if your engine is high hour, or runs a ton of compression and a big cam that develops lots of top end power.

If you want an extended rev limit, have the engine built to use it, and are willing to take the associated risks, I recommend the MSD unit, or a modified 400EX box being offered by a few engine builders now. These won't suffer the cold start problems that the XR250 sometimes does.