Mechanical Over-Rev
Thread Starter
Teching In
Joined: Jul 2009
Posts: 9
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Mechanical Over-Rev I had a pretty bad over-rev this weekend at Road Atlanta in my '99 C5 LS1 Corvette.
I downshifted into 3rd way too early coming down the hill into 10A and over revved the engine to about 8K.
It immediately went into some kind of limp mode almost like the traction control kicked in, but it was not on. I had to limp it off the track and thought I had blown it up. Within about 30 seconds though, it seemed to come back to life and I was able to go back out the next session and run the fastest lap of the weekend at 1:34.44.
A buddy of mine says car may have 2 limiters similar to the old Ford SHO. The first "soft" limiter is set at 6,200rpm and the "hard" limiter is somewhere much higher for cases like what I did. I know there's no way to limit a mechanical over rev, but something like that definately happened. Any ideas?
Here's the video. Watch the tach and listen to the tone of the engine change when it hits about 8,000. I tried to get back in the gas after turn in, but there was no power whatsoever.
http://www.youtube.com/watch?v=H2hgX...layer_embedded
I downshifted into 3rd way too early coming down the hill into 10A and over revved the engine to about 8K.
It immediately went into some kind of limp mode almost like the traction control kicked in, but it was not on. I had to limp it off the track and thought I had blown it up. Within about 30 seconds though, it seemed to come back to life and I was able to go back out the next session and run the fastest lap of the weekend at 1:34.44.
A buddy of mine says car may have 2 limiters similar to the old Ford SHO. The first "soft" limiter is set at 6,200rpm and the "hard" limiter is somewhere much higher for cases like what I did. I know there's no way to limit a mechanical over rev, but something like that definately happened. Any ideas?
Here's the video. Watch the tach and listen to the tone of the engine change when it hits about 8,000. I tried to get back in the gas after turn in, but there was no power whatsoever.
http://www.youtube.com/watch?v=H2hgX...layer_embedded
TECH Enthusiast
Joined: Mar 2005
Posts: 566
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From: Dallas
It's ok... don't worry about it. If you do it and it sings to 9K or higher, then checked the valvetrain if your really worried about it or hear ticking.
I had done a nasty 100mph downshift into 2nd, lost 2 whp but the valvetrain was getting redone anyways. I ended up flat spotted all 4 tires in a fury of smoke.
There's no "hard" limiter on the cars, no electronics can override the drivetrain physics.
But I've done softer mech over-revs between 6 to 8 times, I forget how many times.
If this was an import engine, then you should absolutely be scared of over-rev.
I had done a nasty 100mph downshift into 2nd, lost 2 whp but the valvetrain was getting redone anyways. I ended up flat spotted all 4 tires in a fury of smoke.
There's no "hard" limiter on the cars, no electronics can override the drivetrain physics.
But I've done softer mech over-revs between 6 to 8 times, I forget how many times.
If this was an import engine, then you should absolutely be scared of over-rev.
i'm gonna increase my rev limiter to 7600 TECH Enthusiast
Joined: Mar 2005
Posts: 566
Likes: 0
From: Dallas
^^^ I can't tell if that was sarcasm or not.
But if your cam profile and valvetrain brings ya power, then why not let the baby sing?
I have my rev limiter set at 6500 purely for durability reasons and so I've never dyno'd beyond that point either.
But if your cam profile and valvetrain brings ya power, then why not let the baby sing?
I have my rev limiter set at 6500 purely for durability reasons and so I've never dyno'd beyond that point either.
but good advice. im runin stock Ls1 now to 6000 on a c5 and will prob push it to 6400 soon with a 224 cam install. unless i upgrade the rod bolts too, then she will go to 6800 
thanks!
You probably bent some push rods. I'd check them before you snap one in half like I did! I missed 3rd and went back into 1st around 80mph, (Ls1 Camaro) everything was fine for months, then long story short....push rods were bent and the valve springs were gone.
