i am pretty motivated to get a big gun rev box for my 2005 honda 400ex and for the $ i want to know if they give the ultimate performance, but do they tear up ur engine???

 

The cdi won't hurt your motor a bit, its the guy turning the throttle that does all the damage !!!! [img]i/expressions/face-icon-small-happy.gif[/img] I have +1000 rpm cdi's in my 300ex and 440ex, both have been in for a year or more, absolutely no problems so far, helps get a bit more power out after pipe/filter/airbox mods, Honda has a very low rev limit, and it chokes out power increases that let your motor rev freeer or higher. The only bad thing I have heard is some brands need a fully charged battery, or you will have starting problems. I have White Bros. rev limiters, both quads start just fine.

 

Any time you spin an engine faster than designed, you are increasing piston velocity and stress on various engine parts.

As long as it isn't too insane, I don't think you would reduce engine life that much.

I'm not too familiar with the 400ex, but generally speaking engines are usually set up so they rev above peak HP anyway, so raising the rev limiter generally gives the best gains with other modifications (timing, cam, filter/muffler) that tend to raise where the HP and torque peak.

 

redline is normally where the oil pump can no longer keep up and that the engine parts start to make metal to metal contact. I would never go above it- I drove threw montana a few years ago when there was no speed limit and kept my infinity G20 at the redline for a hours- it ended up kicking a rod a few days later with only 60k on the engine with fresh oil topped off. that was a $3,000 lesson, but i also now have a turbo SR20DET monstor under the hood [img]i/expressions/face-icon-small-smile.gif[/img]

 

JRM good point w/ the oil theory...

also i would say that if your internals are properly balanced then the internals would not have a problem being pushed... to an extent
specifically the crank and rod.

on a fully stock motor i probably wouldn't recommend anything over a stg 1 rev box.... with better internals you could step to the stg 2 or 3

i would be a little hesitate to go wide open for hours upon hours.... honda has done a little r&d.... i'm sure they have thoroughly test their motors....

and i'm not saying that the aftermarket boxes haven't but they have simply found a way to squeeze more power out of the motor....

the more it is pushed at the top the quicker you will burn it up

the other thing is: what else do you have done to your quad pipe/ jeted/ cam ?

 

Everyone has very good points, and I agree, excessive rpms for long periods will kill any motor, the purpose of the higher rev limit is to allow the power band on a modified motor to be used to its full potential. The stock cdi on my son's 300ex was so low, that after a pipe, filter and drilling the air box lid, it felt LESS powerfull than stock, because it revved so nice, it almost immediately hit the rev limit and would sputter and stumble,making you shift constantly,and then you could not run at full throttle in ANY gear, because it would hit the limit. With the +1000 cdi, it allows you to tap into the power band all the way up the rpm curve,the motor is not straining or sputtering (as long as jetting is correct), and you get all the performance the exhaust/intake is letting you have. These quads are trail ridden, ran on MX loops (rarely) and the odd trip to the gravel pit or dunes, and I have not had one engine related problem in a couple of years, that said, I am also not running them with the throttle pinned constantly, but they are run hard and fast, when the opportunity arises. So to sum it up, if you have opened up the intake/exhaust on your quad, and want to use that power more effectively, by all means get a modded cdi, but, remember, it isn't a "magic box" that instantly bolts on power, it works with the mods to allow all the extra power to be available.

 

A person kind of has to look at the design goals of the machine in question, too.

With the 400ex, I think the goal was to build a fun but reliable sport quad with a long engine life.

In a more race oriented model, the balance between performance and longevity would be a bit different.