Opinions on 3.0 high rev incident

[mgerber]

Well, I had fun yesterday...(my car is a stock '81 SC with stock 3.0 CIS motor that was freshened with new studs, bearings and all required head work 4K miles ago)

Was accelerating into the left lane on the highway when the car started accelerating on its own in 3rd gear. To avoid hitting the car in front of me and get on to the right side highway shoulder I put the car in neutral (to try and coast). The tach was buried through the process as I was occupied trying not to kill anyone. Apparently the cruise control malfunctioned and stuck open.

I have read that these cars have 6850 +/- 150 rpm limiters. I could not say where the tach was during all of this, but it looked like it was at about 7K rpm. Car starts hot/cold fine, runs with power as before and no noises after the incident. Any opinions on 3.0 high rpm tolerance? I know the 10mm rod bolts fare better than the 9mm rod bolts in these situations.

Thanks in advance for the input...

[Rrrockhound]

As you found out, the cruise control doesn't coast in neutral. The owner's manual warns you to avoid neutral when the cruise is on.

[mgerber]

Thanks Rrockhound. I would feel better if I had been using the cruise and it was operator error. The d%$n thin came on by itself and stuck wide open - I had to disable it by disconnecting the cable. Pulled the relay too. Have not had time to diagnose it, but after that incident it is heading for the garbage can...

[Gogar]

Sorry about your misfortune. Over the years, with sticky carbs on bikes and unpredictable cars, I've trained myself to go right for the ignition key every time. But it's definitely hard to think straight in those situations.

If you're not noticing any weird noises, maybe you came out ok. Maybe a leakdown test would make sure you didn't mess up any valve stuff.

[AntiCHP]

It's when you grab the wrong gear in a down shift that'll rock your world (say out of 5th and into 2nd...).

In your case, you're pretty much protected by the rev limiter. You may want to have the vavles adjusted to make sure things haven't become too tight or two loose, but otherwise you're probably in the clear.

There's a reason Road & Track had referred to the 78-83 SCs as "the most durable car know to man".

If you had a bent valve, you'd definately notice a decrease in performace... or a car that "fails to proceed" as Rolls-Royce folk say.

Chalk it up to experinece and but that cruise in the crap can.

Happy driving!

[porschenut]

Originally Posted by Gogar

I've trained myself to go right for the ignition key every time.

Yep, just make sure you put it immediately back to the "on" position to avoid engaging the steering lock!

[the]

it's not overreved, don't worry about it.

the only way to overrev and damage a stock SC is to do it mechanically, i.e., downshift into the wrong gear and have the drive wheels mechanically overrev the engine.

[SteveinTO]

On my '82 you can turn the ignition key off and the steering wheel will not lock until you remove the key. When the throttle sticks for whatever reason, go for the brake and the key.

[Wayne 962]

On the SC, you can't really damage it in this fashion, as the rev limiter works well in this case. I suspect you're fine, just fix the problem so it won't happen again with a less fortunate outcome!

-Wayne

[ramonesfreak]

same thing happened to me last season. however, i thought it was my cruise control brain and it was not. turned out to be the throttle cable mount in the engine compartment. the plastic mounting bracket was cracked. my engine has run fine every since, though i was quite worried at first

[Hugh R]

Don't know SC's but if it still runs fine, adjust the valves and move on. You got lucky.

[ramonesfreak]

this is the piece i referred to. check yours. some JB weld fixed mine

[joetiii]

oh wow.... they make cruise control on a 911??????

If it don't go go ticky ticky then u ok

[RSTarga]

I can't believe you guys use cruise control!! And on an on ramp? These aren't caddies.

[ramonesfreak]

i happen to love my cruise control whilst cruising the highway, enjoying a cigarette and a cup of coffee

for the record, original poster, i was NOT using my cruise control when my throttle stuck. Do a search. There are many instances of this happening to many people. There are at least 6 ways for your throttle to get stuck

[mgerber]

Thanks guys for all the input. I will sleep a bit better tonight. One sound piece of advice seems to be to check the sump screen for copper from the bearings during the next few months which I plan to do.

BTW: I wish I were using the cruise control when this happened as I would be less aggravated. I have never used it nor do I plan to. Maybe this was its way of coming to life and getting back at me for being ignored for years...

[ramonesfreak]

lastly,
i would be more concerned about the source of this problem than the health of the engine at this point. i came within a few inches of crashing at high speed, into a cement wall when mine stuck.

dont assume your cruise control brain suddenly "came to life' . highly unlikely. its a cable stuck somewhere, or getting tangled with the clutch cable in the tunnel

good luck

[tshih]

I would always try using the brakes. The brakes are strong enough to over come the engine anytime in any Porsche post 1970. Both feet in when car gets a mind of its own on road or track.

Engine is rated at 200 brake HP, SC brakes are probably rated at 800-1000 HP.

[geoz]

Originally Posted by Rrrockhound

As you found out, the cruise control doesn't coast in neutral. The owner's manual warns you to avoid neutral when the cruise is on.

actually i don't think this is correct; at least on my carrera when i push the clutch the cruise control cuts out and re-engages when the car is back in gear.

looks like the thing malfunctioned on a more substantial level.

cheers

georgie

[Jess]

If the car idles and starts as normal, you're probably fine.

Zip tie the cruise control cable to its bracket so it won't happen again.

As others have said, mechanical over-rev is your enemy here. The car is ok.

Jesse