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Old 07-04-2017, 07:51 PM   #15
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So I just now was going to upshift to 4th, but I misdownshifted to the 2nd at 93-98km/h. The revved just passed the redline like about 7700, 7800rpm...
That that gonna cause a huge damage for the engine and the clutch?
I could be way off, but your chances of damaging the engine from over-reving for a second is analogous to smoking a single cigarette and worrying about lung cancer. Over-reving isn't really the end of the world. If you maintained your revs in the red under heavy load then that would be bad, especially in situations when there is a poor tune, excessive heat, extra stress/hp or other factors that could occur outside of a stock motor.
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Old 07-04-2017, 09:56 PM   #16
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Different members mentioned an occasional mis-shift. I haven't heard anyone to have problems afterwards. In fact the chances after a mis-shift are to have an accident (you lose traction), than to have issues with the engine.
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I could be way off, but your chances of damaging the engine from over-reving for a second is analogous to smoking a single cigarette and worrying about lung cancer. Over-reving isn't really the end of the world. If you maintained your revs in the red under heavy load then that would be bad, especially in situations when there is a poor tune, excessive heat, extra stress/hp or other factors that could occur outside of a stock motor.
Even a brief over rev can be disastrous. But that is if you drop a couple of gears and shoot it up a 1,000 or more RPM. This is when you bend and break things that are just not designed for that sudden or intense of an impact. It is the abruptness of the increase that causes issues not the duration.
In this case dropping one gear and going up a couple of hundred (which as pointed out is about all you could do at that speed) is not going to harm anything. The cut off isn't a drop dead line where one RPM over is going to blow an engine. There is a safety margin built in to deal with exactly this sort of situation.
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Old 07-05-2017, 12:29 AM   #17
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How do you manage to drop it into 2nd gear, were you aggressively driving? 4th gear from 3rd should be a short downward movement, especially on this car.
I was kinda aggressive at that time. Usually I have no problem shifting to 4th from 3rd. I just don't know why either I would misdownshifted to 2nd tbh.
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Old 07-05-2017, 12:35 AM   #18
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Ah, you're fine. Even Shiv's Open Flash canned tunes replace factory rev limit at 7400 with a soft cut at around 7800-ish. I don't remember exact numbers but it's a significant increase.
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Old 07-05-2017, 12:38 AM   #19
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Even a brief over rev can be disastrous. But that is if you drop a couple of gears and shoot it up a 1,000 or more RPM. This is when you bend and break things that are just not designed for that sudden or intense of an impact. It is the abruptness of the increase that causes issues not the duration.

In this case dropping one gear and going up a couple of hundred (which as pointed out is about all you could do at that speed) is not going to harm anything. The cut off isn't a drop dead line where one RPM over is going to blow an engine. There is a safety margin built in to deal with exactly this sort of situation.

Here are some points that cover my thoughts:

https://www.google.com/amp/s/amp.red..._of_an_engine/

Essentially the limits to revving seem to be with handling the heat/friction from the increased speed, handling the forces on parts like the pistons from the increased speed and finally handling the air flow required to not bottleneck the process.

My thoughts are that the forces are too temporary and the heat isn't able to build enough to matter.

The example that comes to mind that is relatable is how the foot experiences two to three times a person's bodyweight when it strikes the ground during running. So a 150lb person experiences 300-450lbs on one foot. Most people would buckle their ankle under that constant load if it wasn't for a half second like it is with a foot strike. Moral of the story is that peak forces may not matter as much as sustained forces. And there just isn't enough time in my opinion for enough heat to build to effect spring recoil or to cause bearing surface breakdown/thinning.


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Old 07-05-2017, 12:45 AM   #20
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That doesnt really cover over-revving. A motor will pop after less than a second if it is over-revved in excess of 1k rpm; 100rpms is much more forgiving. The excess of the rpms is more determinative than the duration.
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Old 07-05-2017, 06:22 AM   #21
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Originally Posted by Irace86.2.0 View Post
Here are some points that cover my thoughts:

https://www.google.com/amp/s/amp.red..._of_an_engine/

Essentially the limits to revving seem to be with handling the heat/friction from the increased speed, handling the forces on parts like the pistons from the increased speed and finally handling the air flow required to not bottleneck the process.

My thoughts are that the forces are too temporary and the heat isn't able to build enough to matter.

The example that comes to mind that is relatable is how the foot experiences two to three times a person's bodyweight when it strikes the ground during running. So a 150lb person experiences 300-450lbs on one foot. Most people would buckle their ankle under that constant load if it wasn't for a half second like it is with a foot strike. Moral of the story is that peak forces may not matter as much as sustained forces. And there just isn't enough time in my opinion for enough heat to build to effect spring recoil or to cause bearing surface breakdown/thinning.


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Ok so take your person running and slam their foot into the ground just once at 2,000 pounds force and you are describing a gross over rev more accurately.
It has nothing to do with heat build up and everything to do with valves, cylinders and other moving parts. They are designed to move at a certain maximum speed and if you exceed that by to much even briefly things start to hit each other. This is what causes damage in an extreme over rev.
Again, you are not going to cause any damage at a coupe of hundred over since redline is a design spec not an absolute.
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Old 07-05-2017, 11:28 AM   #22
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Originally Posted by chulooz View Post
That doesnt really cover over-revving. A motor will pop after less than a second if it is over-revved in excess of 1k rpm; 100rpms is much more forgiving. The excess of the rpms is more determinative than the duration.


Why?


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Old 07-05-2017, 11:41 AM   #23
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Ok so take your person running and slam their foot into the ground just once at 2,000 pounds force and you are describing a gross over rev more accurately.

It has nothing to do with heat build up and everything to do with valves, cylinders and other moving parts. They are designed to move at a certain maximum speed and if you exceed that by to much even briefly things start to hit each other. This is what causes damage in an extreme over rev.

Again, you are not going to cause any damage at a coupe of hundred over since redline is a design spec not an absolute.


Got an example of someone over-revving a motor through missed gear selection for a second while not under load (accelerating) and causing valve float interference or piston/rod force related failure or friction/heat bearing/piston ring failure?


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Old 07-05-2017, 11:57 AM   #24
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Got an example of someone over-revving a motor through missed gear selection for a second while not under load (accelerating) and causing valve float interference or piston/rod force related failure or friction/heat bearing/piston ring failure?


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Not sure what you are saying.
There are thousands of documented examples of miss shift causing severe over rev and causing valve float interference or rod failure .
It is a known failure mode.
There are probably 10 on here alone.
Go check the internet it is all documented for you in great detail.
You study at the Gforce school of physics?
I am sick of debating basic concepts with people that just want to believe their own version of reality.
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Old 07-05-2017, 12:32 PM   #25
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Not sure what you are saying.
There are thousands of documented examples of miss shift causing severe over rev and causing valve float interference or rod failure .
It is a known failure mode.
There are probably 10 on here alone.
Go check the internet it is all documented for you in great detail.
You study at the Gforce school of physics?
I am sick of debating basic concepts with people that just want to believe their own version of reality.


The OP said he hit 7800 rpms and is concerned. You have thousands of examples of engines going over redline by 400rpms for a second and failing? Because I have millions then going over redline and surviving. Im sure you are aware that the true limit of the engine is significantly beyond the manufacturer redline, especially for over revving under nominal conditions like revving in neutral or missing a shift for half a second.

Sure, take the car to redline then accidentally money shift and you are probably screwed. But lets not compare apples to oranges. The OP went 400 over the suggested limit for a second.


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Old 07-05-2017, 01:15 PM   #26
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Couple of hundred is not a big deal Just don't keep doing it. Odds are if you damaged anything you would already know it. Damage caused by a serious over rev is usually (not always but most of the time) immediate and extreme. I wouldn't be worried at all.
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Even a brief over rev can be disastrous. But that is if you drop a couple of gears and shoot it up a 1,000 or more RPM. This is when you bend and break things that are just not designed for that sudden or intense of an impact. It is the abruptness of the increase that causes issues not the duration.
In this case dropping one gear and going up a couple of hundred (which as pointed out is about all you could do at that speed) is not going to harm anything. The cut off isn't a drop dead line where one RPM over is going to blow an engine. There is a safety margin built in to deal with exactly this sort of situation.
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Originally Posted by Irace86.2.0 View Post
The OP said he hit 7800 rpms and is concerned. You have thousands of examples of engines going over redline by 400rpms for a second and failing? Because I have millions then going over redline and surviving. Im sure you are aware that the true limit of the engine is significantly beyond the manufacturer redline, especially for over revving under nominal conditions like revving in neutral or missing a shift for half a second.

Sure, take the car to redline then accidentally money shift and you are probably screwed. But lets not compare apples to oranges. The OP went 400 over the suggested limit for a second.


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Did you even bloody well READ what I said before?
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Old 07-05-2017, 01:27 PM   #27
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I want to attend this Gforce school of physics.
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Old 07-05-2017, 01:33 PM   #28
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I want to attend this Gforce school of physics.

You could get your Uberversity Diploma.
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