Rev Limiters

[islanderman7]

After watching an anime named Initial D (racing series), questions came up. How do Rev limiters work on our bikes (08+)? Like is it controlled by the tachometer or by some electronic computer that I don't know about?

Is it possible to change the limit up to say 14K instead of 13K? And by doing that, would it be a bad thing?

[TnNinjaGirl]

They usually cut either fuel or spark. Seeing that our bikes are carb'd i'd imagine they have a spark cut built into the ignition.

[Sound Wave]

do we even have rev limiters? once i wasn't paying attention and i could have sworn i accidentally got mine up to 15k once. that freaked me out. no limiter ever kicked in afaik.

[TnNinjaGirl]

I've been up to a steady 13k before and have revved it no load to like 15k. No limiter kicked it. If it had a limiter, I imagine it'd be ignition based.

[kkim]

I'm pretty sure I've hit the limiter before when passing cars, but I can't be sure if I'm remembering this on the bike or car. I'll just have to rev it out to redline next time I'm out.

You don't want to increase the cutoff point, if there is one. It's there to protect the engine from revving past it's design limits. I know car guys do it all the time and I know they suffer for their foolishness if they don't have the proper modifications to the valve train.

[Broom]

yes we do have rev limiters. i bounce off mine all the time

its the CDI (electronic ignition box) that does it i believe. its programed to cut the power to the plug at a certain RPM. i don't believe its reprogrammable in any way, but you might be able to get an aftermarket one with a higher rev limiter or something... not sure how it all works.

[Broom]

the only reason i can think of the increase the limit is if you were doing heavy mods to the motor internals to gain more HP and RPMs

[TnNinjaGirl]

From what I understand our bikes don't suffer from valve float as the deciding factor of how high it can rev, but the oiling system just can't keep up with anything much above 13 or 14k.

[islanderman7]

I think my bike has a limiter because when I try to redline it past 13k, the needle on the tach is forced back down to like 11-12k. It won't let me pass 13k.

[kkim]

Originally Posted by TnNinjaGirl

From what I understand our bikes don't suffer from valve float as the deciding factor of how high it can rev, but the oiling system just can't keep up with anything much above 13 or 14k.

um, I know there were oil pressure problems with the pregens and that was a suspected design consideration when they went with the new gen valvetrain decision, but valve float will occur in all engines if revved high enough.

It all has to do with the valve spring rates and the ability to shut at those high revs. Where did you hear about it not being a consideration?

[TnNinjaGirl]

Well ya, you can get any motor to valve float, except for Ducatis I guess. I talked to Chris Hill of Performance Psycle about the characteristics of the newgen 250. He's not a Kawi engineer but he has an idea of what's going on.

I'm not saying it isn't a consideration, just that we would have to rev these things past the point of other things failing before the valves float enough to destroy the motor.

[Alex]

Yup, we've got a limiter. Keep it in first gear, hold it pinned until it doesn't go anymore, and you'll hit the limiter right away. Our tach is optimistic (just like our speedo), so we don't hit the limiter right when it hits the redline, as the engine truly isn't turning at redline yet; there's some fudge factor in there. But the CDI box is most definitely going to cut out at the actual redline.

But cutting spark only keeps you from spinning the engine too fast under acceleration. If we downshift too many gears and dump the clutch, we have the potential of spinning the engine faster than the redline, and bad things can certainly happen at that point.

[kkim]

interestingly, I wasn't able to find any mention of the limiter in either the service or owner's manuals.

[Purspeed]

Don't like rev limiters. Don't like what happens when you don't have a rev limiter.

[Shift250R]

I know for cars they have rev limiters that you can set to what ever rpm. I thought thats what this was about. Then you can rev it up with the clutch in and it wont pass your settings so you can launch off the way you want. It also make a crazy backfire since your limiting under the redline.

[Alex]

I bounced against the limiter a few times yesterday, I had forgotten that the tach goes crazy. About 1000 revs past the listed redline, the engine hits the rev limiter and stays exactly at the same revs, and the tach needle starts bouncing around like crazy. If you back off the throttle, the tach immediately behaves again.