Over rev Box necessary?

[rooster300ex]

With my mods in my sig would a over rev box be necessary? I tried a search and you have to have more then 3 letters to search. cdi,rev,box all to short.

[JOEX]

Add an * to the front or rear of the three letter word;)

[wilkin250r]

Well, your signature lists a high-comp piston and a camshaft upgrade. While I don't know the specifics on the cam, I would imagine it would give a decent upgrade in the higher revs, so I would say "Yes", a high-rev CDI would help you a bit.

For a definitive answer, take your quad to a dyno. Forget the peak HP figure, and look at WHERE you're making power. Compare it to a stock dyno curve. If you're still making power after the stock curve starts to drop off, then a hi-rev CDI would definitely benefit you.

[rooster300ex]

What do ya mean by where i'm making power. do you mean the dyno will read that my powerband is getting cut off by my stock cdi hittin the limiter.

[JOEX]

Check out the dyno section, there are a bunch of graphs posted.

You'll see there will be a peak where the motor is making the most power then soon afterward the power starts dropping off. If your motor is still gaining power at the rev limit you'll wntt a higher rev limit to make use of that power.


Some rev boxes offer a different power curve as well as a higher rev limit. Someone else will have to explain how that works.

[400exstud]

If you have ever seen a dyno chart before you know that their is a distinct drop off in the high RPMs. Well the stock CDI is good for the stock powerband but if you have a motor that is built to make more power in the high rpms the stock CDI may be limiting your motor if it keeps making power after the CDI hits its limit.

[humblesquirel21]

you dont nesicarily have to still be "gaining" power but if there is usable power with it still being in the higher hps or ftlbs defiently and for what itll cost u with the mods u have i would defiently do it

[wilkin250r]

Originally posted by JOEX
Some rev boxes offer a different power curve as well as a higher rev limit. Someone else will have to explain how that works.

I FIGURED IT OUT!!!

Ok, "figured out" isn't really correct. Rather I "learned about" ignition timing, and different ignition curves.

However, I really only researched the "hows and whys" for a two-stroke. While a lot of it will relate to 4-stroke, some of it doesn't (like pipe effect).

[wilkin250r]

Originally posted by rooster300ex
What do ya mean by where i'm making power. do you mean the dyno will read that my powerband is getting cut off by my stock cdi hittin the limiter.

Do you want the long version or the short version?

400exstud and humble have already posted the short version.

[JOEX]

Originally posted by wilkin250r
Do you want the long version or the short version?

400exstud and humble have already posted the short version.
Well, lets hear the long version:D

[wilkin250r]

Originally posted by JOEX
Well, lets hear the long version:D

Oh, alright, just because it has been a while since I've done a long technical post.

This dyno graph was taken of the CT website. This is for a 400EX, but the advice I'm going to give you pertains to ALL quads.

The stock curve is blue. See how the power peaks about 6500 rpm, that's the highest point. Out at 8000rpm, it's still making a bit of power, just not as high as peak. However, by the time you get out to 9000rpm, it's only at 20hp, not very much. The stock rev limit kicks in at 9000rpm, so the graph stops there.

Why is the stock rev limit at 9000rpm? Well, you want a rev limit somewhere, to prevent the engine from over-revving and causing damage. In reality, you're not going to damage anything until about 11,000 rpm, although you will shorten the engine life.

But why 9000 on this engine? Because the power is dropping off really fast, revving any higher isn't going to do any good. If you had a high-rev CDI, the dyno graph would just show the power falling into the dirt. It's not making any useful power after 9000rpm, so why would you waste money on a CDI that allows you to rev further?

However, look at the red curve. Forget the actual HP numbers, and look at the RPMs and where the motor is making power. It peaks much later at about 8000rpm, and at 9000rpm it is still making 36HP. That is respectable and usable, you certainly don't want it to cut off there. Although it's not as high as peak, the engine is making usable power up to about 10,000 rpm, so you certainly wouldn't want to cut it off at 9,000.


http://www.ctracing.com/400ex%20vs440mid%20range.gif