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Hillbillie Mod
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Discussion Starter #1
Im just wondering how detrimental over-reving the engine is.

I read in another thread on here that the limiter doesn't/can't work during downshifts. I noticed at my last track day on Mon., where I had to grab two downshifts, it sounded like I was really reving the engine.

No I didnt' look down to see what the tach was at, so perhaps I wasn't, but it sure sounded like it. And if thats the case, what parts of the engine will that wear out the quickest? Or is the engine fine untill it blows?

I realise, some have said the stock tach is off some, but Id still like to know how hard Im being on the engine!
 

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I was one of people who said that, and again it's simple physics. Over rev on downshifts, In my experience what happens is you'll bend a valve. Easy enough to check, with a compression test on the cyclinders. BEST case you'll bend a valve, or pop a spring retainer and have to have the motor dropped and head pulled (thin gasket time!!!) valve replaced. Worst case Valve damages cyclinder and your looking at a total tear down of the motor to replace valve and slug. Also in my experience with older Kawis. the bottom end is built pretty stout (dunno bout the 10R motor yet) But over reving 95% of DOHC I-4 motors will result in head/head component damage. Some people get away with overreving, quite a few times, others it only takes once. HTH
 

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Why on earth were you grabbing two downshifts at MSR with the gearing you have? I would be more worried about over-revving at TWS in turn 1
 

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Hillbillie Mod
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Discussion Starter #4
AraTidwell said:
Why on earth were you grabbing two downshifts at MSR with the gearing you have? I would be more worried about over-revving at TWS in turn 1
Some of us dont slow down for T1 @ TWS! :mrgreen:

:wink:
 

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Supercharged Mod
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If you are over-revving on downshifts, you are getting the sequence wrong. The way you should be doing it, is stay on the throttle until your braking marker, sit up and brake, hold off with the downshifts until you've done some or most of the braking, then do the downshifts in quick succession so that you finish downshifting just before your turn-in point. This minimizes the engine RPM during the downshifts, and it's easier to do it smoothly.

I've seen many riders on track days do the downshifts the moment they finish accelerating, and then brake afterward ... ! ! !
 

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On this bike, I think a nasty mechanical over-rev can kill the high speed (2x engine rpm)generator too.

I think that happened to one of the magazines, probably in 04.
 

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Being more of a straight liner, i frequently hit the limiter :dontknow:
no probs yet, hell i sumtimes free rev and bounce it off 13k :spit:
 

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You did read the question right??? :heyyou: It wasnt about the revlimter at all it was about over-revving. The REVLIMITER only works on acceleration. Over revving on DOWNSHIFTS is a a matter of vehicle speed vs gear selected vs engine revs.
 

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zx-7rking said:
You did read the question right??? :heyyou: It wasnt about the revlimter at all it was about over-revving. The REVLIMITER only works on acceleration. Over revving on DOWNSHIFTS is a a matter of vehicle speed vs gear selected vs engine revs.

exactly. the motor will spin more rpms. It's just that there isn't any spark present at rpms higher then what the limiter is set at.
I also agree with the above in saying that if your grossly overreving the motor like that it's more of a matter of poor gear selection or downshifting too early.
 

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Hillbillie Mod
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Discussion Starter #12
Well yall are definately right about the "premature" downshifting f'sho!

My excuse is that I was haullin and my brake pads were toast. So after a time or two of running outta room to brake, I started downshifting earlier to help slow the bike down...but it still didnt' really help cause there wasn't any weight on the rear tire...

So basically, I was scarred I was gonna run of the track so I was shifting too early...

Toward the end of the day after I thought about blowing my motor, it helped me to wait for that second downshift till later...

Thanks alot for the comments though!
 

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Hillbillie Mod
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Discussion Starter #13
And Andy, no...thats goin from 4th to second, before the rattlesnake...

Ara said Im crazy and shouldn't have used 4th though...:dontknow:

When its on the limiter I shift.


Mavrik...Yes I believe the slipper helps alot on this...in some situations...however...if youre goin fast enough, the slipper wont lock up the tire but keeps it spinning, so that actually helps to over rev the engine...

I think I've got that right...
 

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MAVRIK said:
Isn't That Also Protected By The Slipper Clutch?
To a certain extent yes. The slipper clutch does allow for a difference between the crank and the rear wheel speed. But it does have it's limits as well. Simple physics will win everytime over mechanics. I know of a guy who over revved a ZX-7R on a missed downshift, Bent a valve, and ZX-7R have had slipper clutches on them since 96
 

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O ok limiter works on accel but not on decel, :idea: :dontknow:
Sorry im :badteeth:
 

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TNZX10 said:
O ok limiter works on accel but not on decel, :idea: :dontknow:
Sorry im :badteeth:


well really it works both ways but you only notice it when on the throttle because it overides you. On decelleration you can override it by causing the motor to over-rev.
 

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And how does it work both ways. It's an electronic device that cuts fuel and spark to the motor. Not much fuel going to the motor on deceleration. Granted we are talking about a VERY VERY small window for it to work. But in all honesty it doesnt stand a chance against the Physics involved here. If the Rev limiter kicks in at 13K RPM and you down shift instead of up shifting, the revlimiter isnt going to do squat to keep the motor from over-revving. TWO THINGS can do that. 1 Physics, two grabbing the clutch to defeat number 1. Rev limiter aint gonna do a thing on downshifting
 
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