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Overrev

 
Old 02-12-2019, 03:53 PM
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Default Overrev

So I messed up a bit and threw 1st instead of 3rd at the higher end of 2nd. Maybe like 75-80. Felt the higher than normal rev and the fuel cut off hitting immediately which dropped my speed with a quickness. I also kicked the clutch into neutral. The afterimage of the rev limiter showed 6800-6900. No lights or wired sounds just yet, thoughts?
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Old 02-12-2019, 03:55 PM
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Originally Posted by SGT_G View Post
So I messed up a bit and threw 1st instead of 3rd at the higher end of 2nd. Maybe like 75-80. Felt the higher than normal rev and the fuel cut off hitting immediately which dropped my speed with a quickness. I also kicked the clutch into neutral. The afterimage of the rev limiter showed 6800-6900. No lights or wired sounds just yet, thoughts?
Was the PDR running?
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Old 02-12-2019, 03:56 PM
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Originally Posted by Katech_Jason View Post
Was the PDR running?
No just saw the tach go partially into the red and kick back out.
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Old 02-12-2019, 04:38 PM
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Originally Posted by SGT_G View Post
No just saw the tach go partially into the red and kick back out.
Assuming you were doing 80 in first and you completely let the clutch out that would be an 8000rpm over-rev. It's "probably" fine, but valve springs are cheap compared to LT4 crate engines. I would put new valve springs on it.

Last season I had mechanical over-rev when going from 2-3 at 90mph and hit first. 9000rpm on the PDR data. I realized it very quickly and probably didn't even have the clutch fully engaged. I replaced valve springs as a precaution and checked the spring pressures, which were all within spec.
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Old 02-12-2019, 04:44 PM
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Originally Posted by SGT_G View Post
So I messed up a bit and threw 1st instead of 3rd at the higher end of 2nd. Maybe like 75-80. Felt the higher than normal rev and the fuel cut off hitting immediately which dropped my speed with a quickness. I also kicked the clutch into neutral. The afterimage of the rev limiter showed 6800-6900. No lights or wired sounds just yet, thoughts?
sell it fast. I think this is what most of the ls7 owners do. Then the car runs fine for a while. They forget about the mechanical over rev that occurred then it drops a valve

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Old 02-12-2019, 04:46 PM
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Originally Posted by Mr. Gizmo View Post
sell it fast. I think this is what most of the ls7 owners do. Then the car runs fine for a while. They forget about the mechanical over rev that occurred then it drops a valve
It's a C7Z not C6Z. I just never changed the picture of my old car.
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Old 02-12-2019, 04:54 PM
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Originally Posted by SGT_G View Post
It's a C7Z not C6Z. I just never changed the picture of my old car.
same thing wonít make a difference if itís an ls7 or lt4. Hard mechanical over rev does an engine in. Back in the day a friend power shift first when wanting 3rd in his 396 Chevelle. The car ran fine for a couple of months then dropped a valve.

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Old 02-12-2019, 05:39 PM
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Come on now..... stop trying to scare the hell out of the Op.
More often than not he will be fine. 6900 rpm will not likely hurt this motor.

It is more likely the op could have damaged the transmission.

I am betting neither was damaged.
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Old 02-12-2019, 06:03 PM
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Originally Posted by dar02081961 View Post
Come on now..... stop trying to scare the hell out of the Op.
More often than not he will be fine. 6900 rpm will not likely hurt this motor.

It is more likely the op could have damaged the transmission.

I am betting neither was damaged.

maybe / maybe not. If he was wringing it out in second gear. Thatís probably close to 90 mph when he slammed 1st gear. All the more reason not to buy one of these dogs used.
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Old 02-12-2019, 06:12 PM
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Originally Posted by Mr. Gizmo View Post
maybe / maybe not. If he was wringing it out in second gear. Thatís probably close to 90 mph when he slammed 1st gear. All the more reason not to buy one of these dogs used.
You just can't miss an opportunity can ya... What a clown!
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Old 02-12-2019, 06:24 PM
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If it's not making funny noises, you're probably fine. I remember driving my 65 L79 back in the 70's. We stuffed two girls in the Vette with my buddy and I. I was 6 grand in 3rd gear, tried to hit 4th, but hit the girl's leg straddling the shifter and went into 2nd gear. The tach buried and it felt like i slammed the brakes on. I pushed in the clutch and it idled fine.
Never had an issue with the motor. Still have the 65. Still know the girl.
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Old 02-12-2019, 08:06 PM
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I had a similar issue. 4th to 3rd and caught it with the clutch before it went too high. The tack trace showed as you describe about 6800 rpm, but the PDR and actually data from cosworth tool showed less, about 6500 rpm.

Last edited by djnice; 02-13-2019 at 02:26 AM.
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Old 02-12-2019, 08:25 PM
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Originally Posted by Clspht View Post
You just can't miss an opportunity can ya... What a clown!
Damned if I can understand the constant bashing of the car he owns. Maybe he really owns a Studebaker...
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Old 02-12-2019, 08:27 PM
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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!!

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Old 02-12-2019, 08:31 PM
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I had WS6 Trans Am and just did the heads and cam. I also put 4.73 gears in the rear end. First track night went from high 3rd down to 2nd instead of 4th. Springs were fine. Bent all the valves though, tough night. You would know if thereís a problem. Thanks
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Old 02-12-2019, 08:37 PM
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Originally Posted by jlbjr View Post
I had WS6 Trans Am and just did the heads and cam. I also put 4.73 gears in the rear end. First track night went from high 3rd down to 2nd instead of 4th. Springs were fine. Bent all the valves though, tough night. You would know if thereís a problem. Thanks
Stock LT4 cam is non interference, unlike most of the aftermarket cams!
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Old 02-12-2019, 09:04 PM
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Originally Posted by tertiumquid View Post
Damned if I can understand the constant bashing of the car he owns. Maybe he really owns a Studebaker...
i think of the c7z more like the Edsel of Corvettes.
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Old 02-12-2019, 09:12 PM
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Without data to determine how high the motor was spun I would trust the guy that actually builds race motors for a living (Jason).
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Old 02-13-2019, 08:17 AM
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Originally Posted by Poor-sha View Post
Without data to determine how high the motor was spun I would trust the guy that actually builds race motors for a living (Jason).
Maybe not everyone dont care about swapping valve springs for fun! Do you really think it will fail few thousands miles later??!!
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Old 02-13-2019, 08:54 AM
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Originally Posted by timmyZ06
Maybe not everyone dont care about swapping valve springs for fun! Do you really think it will fail few thousands miles later??!!
Its not fun but neither is blowing a motor. I had a missed shift in my C6Z at Road Atlanta and after talking to Jason I parked the car and replaced the springs myself.
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