[crfrider04]

Does a rev box really increase power, these bikes have mostly bottom end power and look thait power around 9000 rpm anyways, so it seems to me like revboxes are useless

[crfsonly]

yes they really do work. they not only remove the 9800 rpm limit, as you point out, they also have a "hotter" advance curve...so, they will get to peak hp faster than before. will, a rev box take the place of real increased hp from a big bore kit...NO. there is no replacement for displacement...ok, there is NOS but on a CRF150F? that would surely get you membership in the Darwin Awards!

[hondafan]

the rev limiter cuts the power at a certain RPM.
the rev box provides more top end.

if you get one: dont push the motor farther than you think it will go! or you know what can happen.