what's the purposefuel cut off/rev limiter?
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DUH!!! do you any idea how many ppl blow up the engine even with rev limiter. just image a high school kid reving up his engine without a rev limiter. he would rev his engine to show off how loud it is and then BOOMMMM!!!! then the engine would have to be covered by warranty. companies would lose a lot of money. 
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From: New England
The purpose is basic.
To prevent engine damage!
For you to understand much better
I think the proper question, why overrev is destructive?
Perhaps you heard the word "valve float". All rotating mechanical device has a maximum rpm at which it can operate safely. The valves opens and closes as the engine operates under the maximum rpm (redline).
An internal combustion engine of such high specific output is a well choreographed procession of parts narrowly missing each other and vulnerable pieces.
When the valve is close, there is a small amount of clearance between the camlob and lifter. As the camshaft turns at half engine speed, the camlob touches the lifter, raising the valve off its seat to full lift. The cam continues to turn and the valve springs keep the lifter in contact with the backside of the camlobe. The valve is well.
However, when the engine is suddenly spun so fast, the cam actually throws the valve open and the valve springs cannot overcome the inertia to keep the lifter in contact with the backside of the camlobe. Known as "valve float", the valve is open longer than the cam's intended duration. This also means that the exhaust valve is still extended into the combustion chamber as the piston reaches top dead center (TDC). The piston slams into the valve head, bending it over like a nail. At these high rpms, the piston and valves crash into each other hundreds of times per second. By now, the driver has realized his mistake, kicked in the clutch and, as they say, it's all over but the shouting. The loudest sound to be heard now is the sound of your credit card screaming.
In other words, the major moving parts no longer in sych & outside the calculation...that's overrev for you. So, watch out your lead foot. A lot of temptation, you know your engine can go as much as 9K.
To prevent engine damage!
For you to understand much better
I think the proper question, why overrev is destructive?
Perhaps you heard the word "valve float". All rotating mechanical device has a maximum rpm at which it can operate safely. The valves opens and closes as the engine operates under the maximum rpm (redline).
An internal combustion engine of such high specific output is a well choreographed procession of parts narrowly missing each other and vulnerable pieces.
When the valve is close, there is a small amount of clearance between the camlob and lifter. As the camshaft turns at half engine speed, the camlob touches the lifter, raising the valve off its seat to full lift. The cam continues to turn and the valve springs keep the lifter in contact with the backside of the camlobe. The valve is well.
However, when the engine is suddenly spun so fast, the cam actually throws the valve open and the valve springs cannot overcome the inertia to keep the lifter in contact with the backside of the camlobe. Known as "valve float", the valve is open longer than the cam's intended duration. This also means that the exhaust valve is still extended into the combustion chamber as the piston reaches top dead center (TDC). The piston slams into the valve head, bending it over like a nail. At these high rpms, the piston and valves crash into each other hundreds of times per second. By now, the driver has realized his mistake, kicked in the clutch and, as they say, it's all over but the shouting. The loudest sound to be heard now is the sound of your credit card screaming.
In other words, the major moving parts no longer in sych & outside the calculation...that's overrev for you. So, watch out your lead foot. A lot of temptation, you know your engine can go as much as 9K.
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Joined: May 2008
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From: Scotland
^ yep pretty much what he said...
It's just a way to protect your engine from destruction... I think everyone has accidentally activated the rev limiter when driving at least once.... so it's there for the idiots as well as skilled drivers...
It's just a way to protect your engine from destruction... I think everyone has accidentally activated the rev limiter when driving at least once.... so it's there for the idiots as well as skilled drivers...
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Originally Posted by lotus7racer,May 3 2009, 04:10 PM
The purpose is basic.
To prevent engine damage!
For you to understand much better
I think the proper question, why overrev is destructive?
Perhaps you heard the word "valve float". All rotating mechanical device has a maximum rpm at which it can operate safely. The valves opens and closes as the engine operates under the maximum rpm (redline).
An internal combustion engine of such high specific output is a well choreographed procession of parts narrowly missing each other and vulnerable pieces.
When the valve is close, there is a small amount of clearance between the camlob and lifter. As the camshaft turns at half engine speed, the camlob touches the lifter, raising the valve off its seat to full lift. The cam continues to turn and the valve springs keep the lifter in contact with the backside of the camlobe. The valve is well.
However, when the engine is suddenly spun so fast, the cam actually throws the valve open and the valve springs cannot overcome the inertia to keep the lifter in contact with the backside of the camlobe. Known as "valve float", the valve is open longer than the cam's intended duration. This also means that the exhaust valve is still extended into the combustion chamber as the piston reaches top dead center (TDC). The piston slams into the valve head, bending it over like a nail. At these high rpms, the piston and valves crash into each other hundreds of times per second. By now, the driver has realized his mistake, kicked in the clutch and, as they say, it's all over but the shouting. The loudest sound to be heard now is the sound of your credit card screaming.
In other words, the major moving parts no longer in sych & outside the calculation...that's overrev for you. So, watch out your lead foot. A lot of temptation, you know your engine can go as much as 9K.
To prevent engine damage!
For you to understand much better
I think the proper question, why overrev is destructive?
Perhaps you heard the word "valve float". All rotating mechanical device has a maximum rpm at which it can operate safely. The valves opens and closes as the engine operates under the maximum rpm (redline).
An internal combustion engine of such high specific output is a well choreographed procession of parts narrowly missing each other and vulnerable pieces.
When the valve is close, there is a small amount of clearance between the camlob and lifter. As the camshaft turns at half engine speed, the camlob touches the lifter, raising the valve off its seat to full lift. The cam continues to turn and the valve springs keep the lifter in contact with the backside of the camlobe. The valve is well.
However, when the engine is suddenly spun so fast, the cam actually throws the valve open and the valve springs cannot overcome the inertia to keep the lifter in contact with the backside of the camlobe. Known as "valve float", the valve is open longer than the cam's intended duration. This also means that the exhaust valve is still extended into the combustion chamber as the piston reaches top dead center (TDC). The piston slams into the valve head, bending it over like a nail. At these high rpms, the piston and valves crash into each other hundreds of times per second. By now, the driver has realized his mistake, kicked in the clutch and, as they say, it's all over but the shouting. The loudest sound to be heard now is the sound of your credit card screaming.
In other words, the major moving parts no longer in sych & outside the calculation...that's overrev for you. So, watch out your lead foot. A lot of temptation, you know your engine can go as much as 9K.
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Joined: Jul 2008
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^What lotus said is true, but I think the real way that it destroys engines is that the engine just cant handle the stress of the revs.
The valves do have that much stress on them, but what has MORE stress is the con-rods holding the piston. its flying back and forth at crazy speeds! Its basically like playing with a soccer ball on one of those tether things, whipping it back and forth - the faster you go, the more it jerks..eventually, eitheir the con rod goes or the pin holding the piston on or the crank itself will break. The valves also go through similar problems, which might be the weakest point of OUR cars (valve retainers) - thats not necessarily the case with all other cars.
The valves do have that much stress on them, but what has MORE stress is the con-rods holding the piston. its flying back and forth at crazy speeds! Its basically like playing with a soccer ball on one of those tether things, whipping it back and forth - the faster you go, the more it jerks..eventually, eitheir the con rod goes or the pin holding the piston on or the crank itself will break. The valves also go through similar problems, which might be the weakest point of OUR cars (valve retainers) - thats not necessarily the case with all other cars.
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