Rev Box/CDI Ignition

[jt29]

What exactly is this and what does it do for your performance?? Do you need to change anything else on the bike like jetting or anything? It say that you will increase 3 to 5 hp, is it even worth it? And is there any brands of rev boxes out there that you want to stay away from.

[underpowered]

the rev box/Cdi box increase your rev limiter and alter you ignition timing. stay away from the cheap stuff like White brothers, Big gun, and off brand stuff because they are just XR250 rev boxes and can cause hard starting in cold weather. get a good one from GT thunder or TC racing. GT thunder offers two curves, an aggressive one as well as a more mild version. the aggressive one can cause a rough idle. there is also a company making adjustable ones but i have not heard any feed back on them yet as to whether they are good or bad. But as you siad 3-5 HP, that is being very hopeful, i owuld say you will get 1-2 out of it. is it worth it? well that depends. i dont use one because i dont ride in the upper RPM range to need the extra 1000 or so RPM's. i like a tourquer motor so i stay on the bottom end an midrange. i rarely hit my stock rev limiter so for me it is not worth it but other people need the exrta rev's.

[jt29]

Thanks for the info. good wright up, I just have a few more questions. What is the max rev limit on a stock bike? And I changed my front sprocket from a 16T to a 15T. Since I did that I need to shift sooner and I hit me rev limit faster. If I go with a new rev box, which would allow me to rev it out longer. Would that make up the difference since I went one tooth lower on the front sprocket. Or I am I totaly out in left field on that one.

[2004exrider]

Stock is a 15 tooth, if it had a previous owner they must have put the bigger one on. If its a stock 400ex i wouldnt get a rev box for it. No need to get an extra 1,000 rpm's when the bike is making all of its power at 8,600 rpm's. The only bit of performance you will see out of one is if it has an advancement in the timing. But the only time you would see a big improvement out of the extra rpm's is if you had a completely built motor and you need the extra speed. Other than that it is a waste of money.

Jimmy

[jt29]

My bad, I looked at my bike and it is a 14T I went one down from stock. Thanks for the info. I am sticking with the stock rev box.