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Accidental 8,000rpm+ over-rev

 
Old 06-08-2019, 08:25 AM
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TravisSchoech
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Default Accidental 8,000rpm+ over-rev

(1988 4+3 w/3.45:1, SBE with HCI/blower/n2o)

Last night while playing in Mexico I did something I've never done before...

I pulled a money shift from WOT 3rd gear @6400rpm (~95mph) back to 2nd gear and saw the tach flash past 8,000rpm while the rear tires broke loose.

Not sure how I did it, I've been power shifting this car for 3 years and I have NEVER landed the wrong gear. I guess accidents happen?

As soon as I let the clutch out and realized my mistake I upshifted to 4th+OD. I heard a loud ticking, but I had no choice but to limp it home.

I found that I had spit a lash cap from cylinder 2 intake valve. Pushrod is straight, HR lifter is not collapsed, roller rocker is tight. I reinstalled the lash cap and ran the valves. The car fired up and ran smooth as butter.

Now, my question(s):

What are the chances the rod bolts are still OK with a 8-9k spin?

The cam is a 228/[email protected]" .570/.570" lift advanced +4°, did the lifters survive?

With the given cam specs, and the fact that I floated the valves. Did the valves kiss pistons?

I appreciate any constructive input. I'm just trying to figure out if I should trust any of the life left in this motor...
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Old 06-08-2019, 08:45 AM
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dizwiz24
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Did this once on my 93, triple digits , went for 5th and got 3rd

put clutch back in. Thankfully didnt wreck (ive seen a c4 spin while racing when that driver got 1st vs 3rd).

No harm. Everyone told me how my car was now just a time bomb waiting to ‘give up the ghost’. Now the same bottom end has like 540 whp and 60000 miles later.

i think you are golden and wont have any problem

Last edited by dizwiz24; 06-08-2019 at 03:32 PM.
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Old 06-08-2019, 08:55 AM
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TravisSchoech
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Originally Posted by dizwiz24 View Post
Did this once on my 93, triple digits , with for 5th and got 3rd

put clutch back in. Thankfully didnt wreck (ive seen a c4 spin while racing when that driver got 1st vs 3rd).

No harm. Everyone told me how my car was now just a time bomb waiting to ‘give up the ghost’. Now the same bottom end has like 540 whp and 60000 miles later.

i think you are golden and wont have any problem
My car has been a "ticking time bomb" according to most people since I put it together, so I agree with you.

I'm going to take it for a spin today and see if the power is back. I noticed no smoke or noises after I re-installed the lash cap and ran the valves, so I think you might be right.

Now, what about the procharger? I'm running max impeller speed at 6500rpm, I oversped that by a large margin last night. The the P1sc-1 survive?
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Old 06-08-2019, 09:33 AM
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slow_zo6
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You mentioned lash caps. Is this still a gen I sbc?

Last edited by slow_zo6; 06-08-2019 at 09:35 AM.
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Old 06-08-2019, 11:56 AM
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Valve springs are the most vulnerable. Once they go into valve "float" they become weakened and provide less closing pressure - maybe even progressively worse. But you can R&R the valve springs with the motor in the car so not such a big deal and you can continue to drive it and maybe not even notice any different while driving posted speed limits.

And the tach flashing to 8,000 rpm sounds more like tach needle swung to far due to lack of dampening rather than the motor "flashing" to 8,000 rpm.

Any damage to the bottom end is spilled milk now. And if you don't here any knocks or oil burning or loss of oil pressure you can still drive and race the car as before - but that doesn't mean something won't show up later. But you really have nothing to loose for now so don't let it bother you. Or you could be sourcing a replacement motor to rebuild using a rebuildable core. Hey that's really kind'a fun IMHO and I have 4 blocks getting ready for their turn in the machine shop - 3 of them are 400sbc.

Hope this helps ya.

Last edited by cardo0; 06-08-2019 at 11:58 AM.
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Old 06-08-2019, 12:34 PM
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84 4+3
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I wouldn't worry about it if everything is working correctly now. If you did any serious rod bolt damage you'd hear it and see it (in oil pressure.) Maybe drain the oil and check for shavings... that's just me though.
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Old 06-08-2019, 01:38 PM
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Originally Posted by slow_zo6 View Post
You mentioned lash caps. Is this still a gen I sbc?
What lash cap? To be cautious, I would replace the springs and check pushrods, and rockers carefully. I'm on the strip almost every week.
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Old 06-08-2019, 02:57 PM
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I did the same thing to a 1964 tri power GTO back in 1966. I was learning to powershift at wot. rear wheels bounced and squealed a bit but thats all that happened. If no noise, drive on brother.

Last edited by ghoastrider1; 06-09-2019 at 02:11 PM.
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Old 06-08-2019, 03:44 PM
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****** send it!!
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Old 06-08-2019, 05:25 PM
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Maybe you could use a scope to look at the piston tops through the plug bores to see if there was valve interference.
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Old 06-08-2019, 07:08 PM
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Maybe you could just send it

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Old 06-08-2019, 09:11 PM
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I've done it too shifting out of d to od. No catastrophic damage but I don't believe my valve springs were ever the same.
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Old 06-08-2019, 09:58 PM
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If the engine is built to run 8000 rpm it will be fine, i used to have a car with a 351 nascar engine it did 8,500 rpm and loved to rev.
The only problem is the valve collets, the wear is really severe with those large valves.
Had to replace the collets every couple of months on a weekend car, apart from that the bore wear is severe be it critical piston speed or to much fuel splashing the bores.
great for races but not for the street, should be fine to hit high rpm every so often.
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Old 06-09-2019, 09:07 AM
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TravisSchoech
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Originally Posted by cardo0 View Post
Valve springs are the most vulnerable. Once they go into valve "float" they become weakened and provide less closing pressure - maybe even progressively worse. But you can R&R the valve springs with the motor in the car so not such a big deal and you can continue to drive it and maybe not even notice any different while driving posted speed limits.

And the tach flashing to 8,000 rpm sounds more like tach needle swung to far due to lack of dampening rather than the motor "flashing" to 8,000 rpm.

Any damage to the bottom end is spilled milk now. And if you don't here any knocks or oil burning or loss of oil pressure you can still drive and race the car as before - but that doesn't mean something won't show up later. But you really have nothing to loose for now so don't let it bother you. Or you could be sourcing a replacement motor to rebuild using a rebuildable core. Hey that's really kind'a fun IMHO and I have 4 blocks getting ready for their turn in the machine shop - 3 of them are 400sbc.

Hope this helps ya.
The tach is a nice stepper-motor unit driven by the MSD box, so I believe what it said.

Agreed on the spilled milk, I took it for a spin yesterday and all seems well.
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Old 06-09-2019, 09:09 AM
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Originally Posted by Pwnage1337 View Post
Maybe you could just send it

https://youtu.be/mzOUgwsQ_hM
I let it warm up and decided to let it rip. Seems happy.

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Old 06-09-2019, 10:29 AM
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Originally Posted by TravisSchoech View Post
I let it warm up and decided to let it rip. Seems happy.

https://youtu.be/W-2aHXMZwWE
Ah yes, that part of Mexico is my favorite. Not many people know about that top secret vacation spot!

What App did you use to capture the video/overlay speed? Looks cool

Last edited by Pwnage1337; 06-09-2019 at 10:29 AM.
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Old 06-09-2019, 11:04 AM
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Originally Posted by TravisSchoech View Post
I let it warm up and decided to let it rip. Seems happy.

https://youtu.be/W-2aHXMZwWE
How do you drive so fast in reverse?
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Old 06-09-2019, 11:30 AM
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TravisSchoech
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Originally Posted by Pwnage1337 View Post
Ah yes, that part of Mexico is my favorite. Not many people know about that top secret vacation spot!

What App did you use to capture the video/overlay speed? Looks cool
I am running a simple gopro hero5 with the overlays built in. It makes for some very simple, quick to edit videos
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Old 06-09-2019, 11:30 AM
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Originally Posted by cardo0 View Post
How do you drive so fast in reverse?
It's the only way to catch the exhaust note
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Old 06-09-2019, 11:36 AM
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Disagree with the people that problems will show up later.

Thats like saying piston rings will wear out if you drive it too much.

you either broke it or you didnt. And it sounds like you didnt.
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