This is what piston looks like from an overrev
 

Just wanted to share this with everyone...

The pics are Piston 1, 2 and 3.
http://forums.pelicanparts.com/uploa...1510185963.jpg
http://forums.pelicanparts.com/uploa...1510185963.jpg
http://forums.pelicanparts.com/uploa...1510186056.jpg

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

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.

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

How high did you rev?

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

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

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

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

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

How long did it run after the over rev?

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

ARP is better (long story behind that).

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.

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

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.

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

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.

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

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

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.

Correct. RPM limiter cuts off ignition at a set rpm. You can still blow a shift. BUT...

Lets make it simple and exaggerate the situation. Lets take two identical Porsche motors, both with redline at 6500-6700 rpm, and they grenade at 9000 rpm.

You shift in a HPDE at 6500. You miss a shift, based on fixed gear ratios your RPM jumps up 3000 rpm if you go 3-2 instead of 3-4. You just hit 9500 RPM. Kiss your motor good bye. These numbers are for example only, I have no idea what RPM valves hit cylinders...

Now, lets say you did that exact same shift at 6000 rpm and missed. Motor jumps up the same amount of RPM (its a fixed ratio set by the trans gears)... you go 6000 to 9000 rpm (or less).

See the difference? The lower shift point buys you 700 revs in insurance.

The rev-limiter doesn't prevent an over rev from a missed shift. But the shift point determines how high an RPM you achieve IF you over rev.

Imagine doing every shift at 3000 RPM. You could miss a shift each and every time, and nothing would happen. Max rpm= 6000... The lower you set your shift point via the rev limiter, the more room for error you have. Of course, the lower the rpm, the slower the car. For me, shifting 700 rpm sooner has no drawbacks...

Bo

Well... I don't think anyone wants to lower their redline... most everyone I talk to are finding ways to raise their redline.

Buuuuuttt.... one of the things I am going to look at it with my rebuild is to find a setup that reaches power peak sooner and faster. I don't want to have to constantly be at 5000+ rpms to be hitting peak power.
I plan on driving my car on the street and racing it on short tracks and autocross so I need the power curve to happen sooner.

If my power curve happens earlier in the RPM range, then I won't need to constantly wind out my gears to keep peak HP

...and the valve...with the kiss
http://i.turner.ncaa.com/sites/defau...ery-030716.jpg

Advance your cam timing to reach peak power at lower RPM. The best way to find the sweet spot takes a few iterations and some seat time on a dyno.