rev box?!?!?!?!?

[mustang25]

i was considering prchasing a big gun revbox. It costs $130 and increases the rev limit by 750rpm's....is this worth it??? (i have already installed an exhaust, jet kit, and air filter)
-thanks

[400EXTRA]

no it will blow your motor

i was considering buyin one to then i heard to many bad stories about them

[Giz400ex]

Well, I had a Sparks on my 426 and it was a little bit more snappier, better throttle response! But, I did have a little prob with it in REALLY cold weather:(

[400exrider707]

Originally posted by Giz400ex
Well, I had a Sparks on my 426 and it was a little bit more snappier, better throttle response! But, I did have a little prob with it in REALLY cold weather:(

Cause you had a crappy one.

Only good CDIs for the 400ex are TC racing and GT Thunder... because they are made for it and not made for the XR250 like the rest...

[mustang25]

the one i was going to purchase from big gun was especially produced for the 250ex.....do u really think it will blow the motor if it was built for it?

[Old Head]

This is the one I have had for a year now with no problems.http://www.magicracing.com/SRP-CDI-Rev-Box--TRX400EX-99-04_p_132-32.html

Don't see why they would be made for an xr250, wouldn't that be false advertising

[northwest Texas]

Don't see why they would be made for an xr250, wouldn't that be false advertising No and I'll tell you why (if I understand this correctly.

I'm pulling #'s out of thin air here so take that into consideration.

You have say an XR250, XR400, and XR650. They all have limitations regarding the rev limit. Say the 250's is 9,000 and the 400 is 8,250 and the 650's is 8,000.

Because of the similarities between the models, someone figured out that they could take an XR250's "rev limiter" and directly bolt it on an XR400 and gain some additional rpms before signing off. Would you go that route or completely design your own? It fits a variety of models so while it may be an OEM XR250 part but it will work on a 400.

Now I was pretty vague so no one take my analogy or #'s for gospel. Just trying to make a point that it's not misrepresentation.

[81 clark racing]

if you have a stock motor dont bother buying one. the motor cuts out even before you get that extra amount of rpms if you have diff gearing then you might notice it a little bit more cuz you will be able 2 rev out the motor more and be able to pull the gearing and gain more top speed. imo there 100% junk nothing but problems and yes big gun wb etc are just the 250 rev boxes and they were bulit for a kick start motor not electric this is why it drains your bettery and kills it. even worse in the winter if you dont have you battery charge 100%.also it will not blow your motor its you who blows your motor and holds it pinned 5th gear wide open or in any gear pinned. common cents is shift up but when your in 5th tacked theres where u blow your motor.

[400eXr1d3rZ]

Originally posted by 400exrider707
Cause you had a crappy one.

Only good CDIs for the 400ex are TC racing and GT Thunder... because they are made for it and not made for the XR250 like the rest...

Like the rest? Got anything to back that up with?

I have a procom magnum cdi and it works great.

[400exridin121]

For that price check these out, mostly 1000 more rpm for less http://search.ebay.com/search/search.dll?from=R40&satitle=250ex+cdi

[MO-EX-RIDER]

i have a rev max box and only gave $69 from gwc and it has been great.. it WILL NOT blow up your motor like 81 clark was saying. just buy it and find out for yourself if its worth it???

[alf44]

I had a white bros one on my 440 and overreved my motor one to many times and it welded the sparkplug to the piston. Ruined the whole head and piston.
Now I also have one on the wifes bike that is just piped and jetted and it really makes it snappier but, is harder to start ecspecially when its cold out. I think rev boxes are pretty much a gamble!

[AbnMP13]

I have a WB and like it, I can start it in reverse (and I did not cut any wires) and have zero cold starting issues.

[300exguy125]

i have a big gun rev box for my 300ex and i have been having some sarting problems in the winter but other than that if its warm out side it works great and once it starts in the cold it runs and i had have no problems except letting it sit out in the cold while i go do something then try starting it

[deathman53]

the main problem with them and why they are harder to start and require a fully charged battery is that the spark doesn't kick in to about 750 rpm, they were designed for a kick start engine. The electric start has trouble to turn the motor over that fast. I did a experiment with my 01 xr250r and friends 400ex, he had a wb rev box and he had his stock one. I put his on my dirtbike, it started easier, put his wb box on my dirtbike, it started and ran almost exactly the same as my stock one(and looked identical also). Then he put my stock box on his 400ex, it acted exactly the same as his wb box. The conclusion we came up with is that, the wb box is a xr250r box. His wb box had some number scraped off it, wouldn't you know the part of the numbers you could see, matched my xr250r's box. I don't know about the gt thunder box, big gun, or sparks, as I never seen them. We didn't have a xr400 to compare the rev boxes to.

[deathman53]

a commonly done mod for racers on a 250x was to use a 350x cdi box, for almost unlimited revs. That didn't suffer the starting problems as both are kick start.