Overrev
#21
Instructor
Agree with dar02081961. Thats why GM has mechanisms in place to prevent damage. The fuel shut off occurs well before a potential catastrophic event can happen. The LT4 is bullet proof. Unless you hear something, just drive the car!
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timmyZ06 (02-13-2019)
#22
Le Mans Master
Ls7 is a whole is a whole different story! When mine happened it didnt really had time to overreved too far, but it happened few times! I was listening for weirds noises . Maybe i got lucky, but after the LDT was sure about no damages. Once gain, its super easy to go in 1st instead of 3rd, i dont get it!!
#24
Drifting
Lucky this isn’t a Porsche which logs every overrev and would result in diminished value on sale.
#26
Drifting
#27
Definitely sell it NOW, and really, get an automatic, much quicker and no missed shifts...........
#28
Pro
Thread Starter
#29
Tech Contributor
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Bill
#30
Premium Supporting Vendor
I'll go back to my response and use of the word "probably". "Probably" and the cost of replacing an engine don't go together for me. I would rather replace valve springs than risk it. Like I said in my instance of over-rev last year, the valve springs were within spec still. I wouldn't want to worry about it for future track days though.
FYI - even 9000rpm over-revs don't typically fail engines immediately. They can fatigue valve springs which can lead to failure later. That's why you hear people say "I was just driving down the highway and the valve spring broke", failing to mention the mechanical over-rev on the track day the weekend before. We have had 9000rpm over-revs in World Challenge engines and finished the race. When it's a sprint race and GM cared more about winning than hurting an engine they just went for it. Of course, valve springs got changed after the race if not a whole rebuild.
FYI - even 9000rpm over-revs don't typically fail engines immediately. They can fatigue valve springs which can lead to failure later. That's why you hear people say "I was just driving down the highway and the valve spring broke", failing to mention the mechanical over-rev on the track day the weekend before. We have had 9000rpm over-revs in World Challenge engines and finished the race. When it's a sprint race and GM cared more about winning than hurting an engine they just went for it. Of course, valve springs got changed after the race if not a whole rebuild.
#31
Technically what folks are saying is correct and what can happen during a "over rev".
A mechanical 'over rev" is a physical condition based on the mechanical capabilities of the valve train, the bottom end rods and rod bearings.
And all of the things you mention can occur during a "mechanical over rev".
Generally any damage done during a mechanical "over rev" will show itself within 10-20 thousand miles probably sooner. (just a swag here to make a point later).
However in this case the OP states the information available to him indicates the engine didn't exceed 6900 rpm or so.
While we all know the rev limiter on the LT4 is electronically set at 6600 rpm from the factory, we also know 6900 rpm is not really an "over rev" for an LT4 in mechanical terms.
There are a few folks in the Z06 community pushing these LT4s up to 7000 rpm without any rev related issues.
Not going to get into why they feel safe doing so but there is some solid logic behind it.
My point is the OP should have many thousands of miles of warranty left on the engine/car.
If he actually had a "mechanical over rev" (which the data suggest he didn’t) the damaged components have plenty of time to fail while he is still covered by the warranty.
I agree if you were racing this engine without the factory rev limiter and had unlimited available resources, a valve spring and lifter replacement would be in order.
But for us normal folks based on the information presented, chances are the OP can drive the car long enough under warranty to determine if he damaged the engine.
I am betting he will be just fine.
A mechanical 'over rev" is a physical condition based on the mechanical capabilities of the valve train, the bottom end rods and rod bearings.
And all of the things you mention can occur during a "mechanical over rev".
Generally any damage done during a mechanical "over rev" will show itself within 10-20 thousand miles probably sooner. (just a swag here to make a point later).
However in this case the OP states the information available to him indicates the engine didn't exceed 6900 rpm or so.
While we all know the rev limiter on the LT4 is electronically set at 6600 rpm from the factory, we also know 6900 rpm is not really an "over rev" for an LT4 in mechanical terms.
There are a few folks in the Z06 community pushing these LT4s up to 7000 rpm without any rev related issues.
Not going to get into why they feel safe doing so but there is some solid logic behind it.
My point is the OP should have many thousands of miles of warranty left on the engine/car.
If he actually had a "mechanical over rev" (which the data suggest he didn’t) the damaged components have plenty of time to fail while he is still covered by the warranty.
I agree if you were racing this engine without the factory rev limiter and had unlimited available resources, a valve spring and lifter replacement would be in order.
But for us normal folks based on the information presented, chances are the OP can drive the car long enough under warranty to determine if he damaged the engine.
I am betting he will be just fine.
Last edited by dar02081961; 02-13-2019 at 11:39 AM.
#33
Sorry, didn't mean for it to sound as if I singled you out.
Corrected.
My comments are trying to make the point the OP states in the original post the max rpm he hit was 6900 rpm.
6900 rpm is not a " mechanical over rev" for an LT4.
Corrected.
My comments are trying to make the point the OP states in the original post the max rpm he hit was 6900 rpm.
6900 rpm is not a " mechanical over rev" for an LT4.
Last edited by dar02081961; 02-13-2019 at 11:44 AM.
#34
Premium Supporting Vendor
Technically what folks are saying is correct and what can happen during a "over rev".
A mechanical 'over rev" is a physical condition based on the mechanical capabilities of the valve train, the bottom end rods and rod bearings.
And all of the things you mention can occur during a "mechanical over rev".
Generally any damage done during a mechanical "over rev" will show itself within 10-20 thousand miles probably sooner. (just a swag here to make a point later).
However in this case the OP states the information available to him indicates the engine didn't exceed 6900 rpm or so.
While we all know the rev limiter on the LT4 is electronically set at 6600 rpm from the factory, we also know 6900 rpm is not really an "over rev" for an LT4 in mechanical terms.
There are a few folks in the Z06 community pushing these LT4s up to 7000 rpm without any rev related issues.
Not going to get into why they feel safe doing so but there is some solid logic behind it.
My point is the OP should have many thousands of miles of warranty left on the engine/car.
If he actually had a "mechanical over rev" (which the data suggest he didn’t) the damaged components have plenty of time to fail while he is still covered by the warranty.
I agree if you were racing this engine without the factory rev limiter and had unlimited available resources, a valve spring and lifter replacement would be in order.
But for us normal folks based on the information presented, chances are the OP can drive the car long enough under warranty to determine if he damaged the engine.
I am betting he will be just fine.
A mechanical 'over rev" is a physical condition based on the mechanical capabilities of the valve train, the bottom end rods and rod bearings.
And all of the things you mention can occur during a "mechanical over rev".
Generally any damage done during a mechanical "over rev" will show itself within 10-20 thousand miles probably sooner. (just a swag here to make a point later).
However in this case the OP states the information available to him indicates the engine didn't exceed 6900 rpm or so.
While we all know the rev limiter on the LT4 is electronically set at 6600 rpm from the factory, we also know 6900 rpm is not really an "over rev" for an LT4 in mechanical terms.
There are a few folks in the Z06 community pushing these LT4s up to 7000 rpm without any rev related issues.
Not going to get into why they feel safe doing so but there is some solid logic behind it.
My point is the OP should have many thousands of miles of warranty left on the engine/car.
If he actually had a "mechanical over rev" (which the data suggest he didn’t) the damaged components have plenty of time to fail while he is still covered by the warranty.
I agree if you were racing this engine without the factory rev limiter and had unlimited available resources, a valve spring and lifter replacement would be in order.
But for us normal folks based on the information presented, chances are the OP can drive the car long enough under warranty to determine if he damaged the engine.
I am betting he will be just fine.
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dar02081961 (02-13-2019)
#35
Safety Car
Happened to me at least 5 times!! For the life of me i cant understand why the 1st is so easy to shift compared to the 3rd!! Never happened to me before the C7z!!!
So anyway it ran fine each time afterward, so i wouldnt worry, because damage would be right away!! Changing valve springs is useless , unless it sounds like a broken spring. Mine dynoed 698whp and 757wtq 6 months after that and still run strong!!!
btw a leak down test was performed also 6 months afterward, and was perfect!! A broken spring would have a caused a serious leak!!
So anyway it ran fine each time afterward, so i wouldnt worry, because damage would be right away!! Changing valve springs is useless , unless it sounds like a broken spring. Mine dynoed 698whp and 757wtq 6 months after that and still run strong!!!
btw a leak down test was performed also 6 months afterward, and was perfect!! A broken spring would have a caused a serious leak!!
There is no protection for a mechanical over-rev so slow down your shifts.....if in doubt push the clutch in and let the stick go to natural neutral, which falls between 3rd and 4th. then you know where you are. Unless you are racing for pink slips the insurance this move will give you is worth it to save your motor. I would agree that there should not be any motor damage if ti still runs fine, but if you do this into a curve you will lock up and crash.
#36
Banned Scam/Spammer
Fuel cut-off will only stop you from over-revving your car while accelerating in one gear. A mechanical over-rev condition happens when downshifting. In this case, as soon as the clutch is engaged the engine will rev up on its own to match the speed it was at in the previous gear. So if you were doing 90mph in 2nd gear and immediately shifted into first the engine will rev up to wherever it needs to be to match 90mph in 1st gear. There is nothing that can prevent this once it is initiated. It can also happen so fast that the tach doesn't have a chance to register just how high it went right away.
#37
Drifting
Stop manhandling the M7. 3/4 is the easiest shift since the M7 always returns to this gate on its own...gentle pressure left/right gets you into 1/2 or 5/6. Hard pressure right and up for 7th. Don’t grab the shifter..use the palm of your hand and the gate springs to guide you.
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timmyZ06 (02-13-2019)
#38
Le Mans Master
Fuel cut-off will only stop you from over-revving your car while accelerating in one gear. A mechanical over-rev condition happens when downshifting. In this case, as soon as the clutch is engaged the engine will rev up on its own to match the speed it was at in the previous gear. So if you were doing 90mph in 2nd gear and immediately shifted into first the engine will rev up to wherever it needs to be to match 90mph in 1st gear. There is nothing that can prevent this once it is initiated. It can also happen so fast that the tach doesn't have a chance to register just how high it went right away.
#39
Intermediate
What qualifications do you possess to give that assessment to the OP or anybody for that matter?
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Lavender (02-15-2019)
#40
Pro
Thread Starter
Honestly I must not have fully releases the clutch because the tracer for the highest point you rev was at the 68-6900 point. If I was really in the 8k range, that tach should've shot hard to the right. Additionally, like I said, I wasn't redlining 2nd but rather at the higher end of it.