rev limit on CBR900 - Honda Motorcycles - FireBlades.org
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post #1 of 15 Old 11-07-2009, 1:19 PM Thread Starter
 
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rev limit on CBR900

I usually shift my 97 cbr900 around 11,000 rpm when I am blowing the cobwebs out of her but today I hit 12,500 indicated on the tac and there was no signs of a rev limiter. Suprized the hell out of me. I know the tac isn't exact but is it that far off. At what rpm on the tac does the rev limiter actually kick in?
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post #2 of 15 Old 11-07-2009, 1:57 PM
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Re: rev limit on CBR900

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Originally Posted by roland5color View Post
I usually shift my 97 cbr900 around 11,000 rpm when I am blowing the cobwebs out of her but today I hit 12,500 indicated on the tac and there was no signs of a rev limiter. Suprized the hell out of me. I know the tac isn't exact but is it that far off. At what rpm on the tac does the rev limiter actually kick in?
Tried searching for some dyno charts and it looks like it's around 11,500RPM on the dyno's tach but that doesn't tell us what the bike's tach might be indicating.
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post #3 of 15 Old 11-08-2009, 4:34 AM Thread Starter
 
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Re: rev limit on CBR900

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Originally Posted by bladeracer View Post
Tried searching for some dyno charts and it looks like it's around 11,500RPM on the dyno's tach but that doesn't tell us what the bike's tach might be indicating.
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Thanks for the help blade. That would put my tack off by at least a 1000 rpm or so. Which is easily believable. Well at least now I know that I can wring her neck a little more without bumping the limiter. I will have to get a more accurate device to measure the rpms I to find out how far my tack is off.
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post #4 of 15 Old 11-08-2009, 5:45 AM
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Re: rev limit on CBR900

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Thanks for the help blade. That would put my tack off by at least a 1000 rpm or so. Which is easily believable. Well at least now I know that I can wring her neck a little more without bumping the limiter. I will have to get a more accurate device to measure the rpms I to find out how far my tack is off.
If it's in neutral the tach will go well above the limiter but I'm assuming you mean that you revved a gear out to 12,500TPM?

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post #5 of 15 Old 11-08-2009, 6:17 AM Thread Starter
 
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Re: rev limit on CBR900

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Originally Posted by bladeracer View Post
If it's in neutral the tach will go well above the limiter but I'm assuming you mean that you revved a gear out to 12,500TPM?
You would be assuming correctly. I would never rev a bike to the limiter in neutral. To me that is motorcycle abuse. Normally I don't rev the bike to the limiter at all. I try to shift about 500 rpm before it kicks in. I have only had the 900 for a few months and I always assumed that the rev limit was about 500-1000 rpm past the 11,000 mark on the tach so I would just shift at 11,000 but this time I held the throttle a little longer than usual. Now this was in third gear so I was moving pretty good and only caught a glimpse of the tach but I know it was past 12,000. May have only been 12,200 or 12,300 but it was sure past 11,500. Is there any chance someone could have removed the limiter or raised it.
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post #6 of 15 Old 11-08-2009, 6:23 AM
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Re: rev limit on CBR900

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Originally Posted by roland5color View Post
You would be assuming correctly. I would never rev a bike to the limiter in neutral. To me that is motorcycle abuse. Normally I don't rev the bike to the limiter at all. I try to shift about 500 rpm before it kicks in. I have only had the 900 for a few months and I always assumed that the rev limit was about 500-1000 rpm past the 11,000 mark on the tach so I would just shift at 11,000 but this time I held the throttle a little longer than usual. Now this was in third gear so I was moving pretty good and only caught a glimpse of the tach but I know it was past 12,000. May have only been 12,200 or 12,300 but it was sure past 11,500. Is there any chance someone could have removed the limiter or raised it.
I don't know about raising it but I'm sure it's possible to remove it entirely.

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post #7 of 15 Old 11-08-2009, 12:24 PM
 
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Re: rev limit on CBR900

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I don't know about raising it but I'm sure it's possible to remove it entirely.
Either is possible with custom programming in the ECU, no way to do it otherwise.
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post #8 of 15 Old 11-08-2009, 12:35 PM Thread Starter
 
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Re: rev limit on CBR900

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Either is possible with custom programming in the ECU, no way to do it otherwise.
I knew you could program newer fuel injected bikes but I wasn't sure about 97 CBR900. I know the previous owner had the bike dyno tuned. Maybe he had the limiter raised. Hopefully I will have a shift lift soon and I won't have to worry about it so much. Thanks for your reply
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Re: rev limit on CBR900

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Originally Posted by roland5color View Post
I knew you could program newer fuel injected bikes but I wasn't sure about 97 CBR900. I know the previous owner had the bike dyno tuned. Maybe he had the limiter raised. Hopefully I will have a shift lift soon and I won't have to worry about it so much. Thanks for your reply
It's possible to reprogram anything that uses programming to operate.

It's unlikely he had the limiter raised, chances are your tach is just off. Just because you rev a bike to a higher RPM doesn't automatically mean it's producing more power, or any engine for that matter. It has an optimal point, which isn't necessarily the rev limit and then power will fall beyond that.
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post #10 of 15 Old 11-09-2009, 11:12 PM
 
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Re: rev limit on CBR900

You can definitely reprogram the limiter but it's very expensive to have someone do it. Back when they had 600 supersport class in AMA dragracing, Schnitz would reprogram your brain but they charged like 1500 bucks for it. I'd just find an old Vance & Hines powerpak if I wanted more rpm's. Btw...if you rev that thing hard often, definitely consider a set of good springs. I have PM's in mine and have ran it up to 13.5 a few times on dyno. Money well spent for peace of mind.
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post #11 of 15 Old 11-09-2009, 11:42 PM
 
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Re: rev limit on CBR900

OK, not to thread jack but...is hitting the rev limiter that bad? Like I never do anyways, but I always assumed that it was OK as that was the purpose of the rev limiter, and there is a safety margin set by the factory (i.e. it could go a bit higher than the rev limiter). And yes, I know that the max hp/torque is below the rev limiter, and that when you go past the sweet spot it is diminishing returns.
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post #12 of 15 Old 11-10-2009, 12:15 AM
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Re: rev limit on CBR900

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OK, not to thread jack but...is hitting the rev limiter that bad? Like I never do anyways, but I always assumed that it was OK as that was the purpose of the rev limiter, and there is a safety margin set by the factory (i.e. it could go a bit higher than the rev limiter). And yes, I know that the max hp/torque is below the rev limiter, and that when you go past the sweet spot it is diminishing returns.
I wouldn't expect a problem in a good strong engine but running at redline or the limiter a lot is over-stressing a lot of engine parts. The more you do it, the more likely something will let go eventually.

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post #13 of 15 Old 09-22-2012, 8:16 PM
 
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Re: rev limit on CBR900

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If it's in neutral the tach will go well above the limiter but I'm assuming you mean that you revved a gear out to 12,500TPM?

does that mean that the rev limiter is raised in neutral? or does the engine ramp up quicker than the rev limiter can suppress it?... also i used to race motocross, when we were jumping, and were nose down in the air, we pin the throttle open to use centrifical force to bring your nose up...now this happened all the time, is there a big difference between hitting the rev limiter on my 99 blade compared to my 08 crf450? what im trying to ask is how bad is it to hit the rev limiter on the blade.
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post #14 of 15 Old 09-23-2012, 12:48 AM
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Re: rev limit on CBR900

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does that mean that the rev limiter is raised in neutral? or does the engine ramp up quicker than the rev limiter can suppress it?... also i used to race motocross, when we were jumping, and were nose down in the air, we pin the throttle open to use centrifical force to bring your nose up...now this happened all the time, is there a big difference between hitting the rev limiter on my 99 blade compared to my 08 crf450? what im trying to ask is how bad is it to hit the rev limiter on the blade.

The rev limiter only cuts the ignition, it is not an engine brake that stops the engine from spinning any higher. If you crack the throttle open at 1000rpm the engine has enough inertia to continue accelerating after the spark is cut. Increasing the revs up to the limiter with a little mechanical affinity in mind doesn't do any harm to the engine and it will happily sit there banging the limiter in neutral all day long.

Whether that is sufficient to damage the engine comes down to whether it's designed for it, and I would expect dirt bikes would have a healthy margin for that very reason. Of course, you wouldn't be doing it in neutral anyway as the crankshaft has very little mass, you would be leaving it in gear and using the centrifugal force within the rear wheel and tyre to alter the attitude of the bike.

The CRF engine though is a very highly strung thing prone to catastrophic failures under race use unless very closely monitored. I've seen a 450 engine that threw a rod and used the remains of the rod to cut the crankcases in half.

Exceeding the limiter usually results in rod stretch on the exhaust stroke with either the beam letting go, the rod bolts failing, or the bigend ovaling to the point that oil clearance is compromised resulting in metal-to-metal contact of the bearing shells at the sides and over-heating.

Simply put, exceeding the manufacturer-dictated rev limit (assuming the engine is factory built of course) is never a good thing for the engine, even if it stays together there's a good chance the rod has been compromised in some way.

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post #15 of 15 Old 09-23-2012, 8:35 PM
 
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Re: rev limit on CBR900

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Originally Posted by bladeracer View Post
The rev limiter only cuts the ignition, it is not an engine brake that stops the engine from spinning any higher. If you crack the throttle open at 1000rpm the engine has enough inertia to continue accelerating after the spark is cut. Increasing the revs up to the limiter with a little mechanical affinity in mind doesn't do any harm to the engine and it will happily sit there banging the limiter in neutral all day long.

Whether that is sufficient to damage the engine comes down to whether it's designed for it, and I would expect dirt bikes would have a healthy margin for that very reason. Of course, you wouldn't be doing it in neutral anyway as the crankshaft has very little mass, you would be leaving it in gear and using the centrifugal force within the rear wheel and tyre to alter the attitude of the bike.

The CRF engine though is a very highly strung thing prone to catastrophic failures under race use unless very closely monitored. I've seen a 450 engine that threw a rod and used the remains of the rod to cut the crankcases in half.

Exceeding the limiter usually results in rod stretch on the exhaust stroke with either the beam letting go, the rod bolts failing, or the bigend ovaling to the point that oil clearance is compromised resulting in metal-to-metal contact of the bearing shells at the sides and over-heating.

Simply put, exceeding the manufacturer-dictated rev limit (assuming the engine is factory built of course) is never a good thing for the engine, even if it stays together there's a good chance the rod has been compromised in some way.
awsome, thats what i figured with the rev limiter allowing the rpms to exceed its set limit by inertia...thanks for the reply, you answered my questions exactly
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