This is what piston looks like from an overrev

[Trakrat]

Just wanted to share this with everyone...

The pics are Piston 1, 2 and 3.

[tocobill]

The bent valves are also a good indication. Judging from #1 and #2 you have couple.

[Trakrat]

sorry... meant to share this on the 911 Technical Forum... since there will be more eyes to see this.

If anyone knows how to move this thread... please do so.

[safe]

A few more hits and you'll have clearance for the valves.

How high did you rev?

[Steve@Rennsport]

Thats a very hard overrev,............

I would be checking the big ends of the rods and I might even replace the rod bolts.

[Trakrat]

Originally Posted by safe

A few more hits and you'll have clearance for the valves.

How high did you rev?

probably ~ 9k rpm I would guess. misshift from 4th to 2nd.

[Trakrat]

Originally Posted by Steve@Rennsport

Thats a very hard overrev,............

I would be checking the big ends of the rods and I might even replace the rod bolts.

yep... I'll be replacing everything with Raceware.

[Tippy]

That piston beat the **** out of that valve! Damn!

[Jeff Alton]

How long did it run after the over rev?

[Tippy]

Originally Posted by Jeff Alton

How long did it run after the over rev?

Couldn't have run at all. It won't build any compression.

[Steve@Rennsport]

Originally Posted by Trakrat

yep... I'll be replacing everything with Raceware.

ARP is better (long story behind that).

[Trakrat]

Originally Posted by Jeff Alton

How long did it run after the over rev?

It ran until I put the car in neutral as I coasted to a stop at a stop light. As soon as the car came to an idle, it died and would not start again with both oil and battery light on.

The engine would turn with the start, but other than a cough here or there, the engine never fired up again.

[Trakrat]

Originally Posted by Steve@Rennsport

ARP is better (long story behind that).

really? interesting... as I've heard horror stories from ARP failures from 10 years ago when I had a 4cyl turbo.

[Trakrat]

Originally Posted by Tippy

Couldn't have run at all. It won't build any compression.

It continued to run long enough for me to go another 1/2 mile down the highway and go up hill to a stop light.
In fact, I didn't think any damage happened, as everything seemed fine for the next minute of driving.
It wasn't until I came to a stop with the gear in neutral that the engine died.

[Reiver]

Must be a heart rending deal when you popped the clutch on second...Stock shifter?

[Tippy]

Originally Posted by Trakrat

It continued to run long enough for me to go another 1/2 mile down the highway and go up hill to a stop light.
In fact, I didn't think any damage happened, as everything seemed fine for the next minute of driving.
It wasn't until I came to a stop with the gear in neutral that the engine died.

That's really odd. So, were there some cylinders that didn't have contact? Mine had much less piston damage, and it was completely dead once I pushed the clutch in and wouldn't start at all. Then again, most of the exhaust rockers broke too.

[Trakrat]

Originally Posted by Tippy

That's really odd. So, were there some cylinders that didn't have contact? Mine had much less piston damage, and it was completely dead once I pushed the clutch in and wouldn't start at all. Then again, most of the exhaust rockers broke too.

nope... all pistons got smacked the same.
Other than the piston head damage on the surface, I haven't found anything else that is as clear of damage.

Even the valve stem heads themselves are in fairly decent shape. Figured with a smack against the piston like that, I would have seen some damage.

I've removed the pistons and all I have left are the rods and case to take apart. Just a visual inspection of the rods doesn't show any of them bent.

[911SauCy]

THIS is the single reason I will not let anyone drive my '78.

The consequences of a single miss-placed shift are grave...

[bpu699]

One form of protection you can do is to set your rev limiter lower... My motors redline is 6700. My revlimiter on the track for HPDE events is set at 6000 with the MSD.

I figure that does a couple things...

If I miss a shift from 3-4 and go 3-2, I have an added cushion. And, I have done that a couple times... No bent bits, no piston hits. I did find out later that my motor has aftermarket springs, I am sure that helps...

I would think on a missed downshift you get the same protection... you are resetting your peak rpm to 700 rpm lower...

Is that a practical solution in racing? Nope.

Does it help with HPDE where there are no trophies and it can save your motor... yep...

6700 rpm on the street... 6000rpm on the track... cheap insurance at HPDE

Bo

[Trakrat]

Originally Posted by bpu699

One form of protection you can do is to set your rev limiter lower... My motors redline is 6700. My revlimiter on the track for HPDE events is set at 6000 with the MSD.

I figure that does a couple things...

If I miss a shift from 3-4 and go 3-2, I have an added cushion. And, I have done that a couple times... No bent bits, no piston hits. I did find out later that my motor has aftermarket springs, I am sure that helps...

I would think on a missed downshift you get the same protection... you are resetting your peak rpm to 700 rpm lower...

Is that a practical solution in racing? Nope.

Does it help with HPDE where there are no trophies and it can save your motor... yep...

6700 rpm on the street... 6000rpm on the track... cheap insurance at HPDE

Bo

It's my understanding that your rev limiter just keeps your throttle from accelerating past redline.

There is no device that prevents you from manually shifting the gears to whatever gear you want that I'm aware of.
I would guess that you would have to have some kind of electronic controlled transmission to keep you from moving that shift lever.