Engine over rev protection question?
 

I am wondering when Porsche incorperated over rev protection into the ingnition electronics. I have a 1980 Euro 911SC and the distributor has a mechanical rev limiting rotor. Should it? Does the ignition circuitry have rev limiting protection which uses a standard rotor?

Thanks!

John

Per Warren:
"According to the '78 - '81 spec book, a 6800 rpm rev limiter rotor was used on the 930/03, 10, and 13 engines."

So let's say your 1980 engine number was 6300427. This would make it a 930/09 (ROW) or a 930/07 (US).

The 930/03 was used for the 1978 & 1979 ROW.
The 930/10 was used for the 1981, 82 & 83 ROW.

So I would conclude you have rev limit redundancy with the rev limiting rotor.

One way to find out.

I think the rev limiter controls the limits of the piston speed to keep it within a safe parameter.
Too much reciprical mass(top 1/3 of rod on up) means that when the crank reaches the top of its stroke everything wants to keep on going, and the most common area of breakage is in the rod bolts. ARP are supposed to be the only ones to use.
Also, a "stroker" crank will wear the rings much quicker.

Not sure about the scale, but I think its:3500 (ft or inch/sec ?) limit for stock, 4000 for aftermarket and 6000 for circletrack built engines where they are rebuilt every race.

ISLAND911, I read in the Bently manual this morning that the fuel pump cuts off after 7000 rpms. So it sounds like I don't need the fancy rev limiting rotor? Is that correct?

John

The six-pin CD box (introduced in 1978) has a rev-limiter built in. I have never tested my SC engine against this however...

-Wayne

early cars had the rev limiter in the distributor rotor, late cars had a fuel shut off. The change occured in the late 70s with the advent of cats, the fuel cutoff was intended to keep raw fuel from being dumped into the cat.

Hmmmm, interesting! My car does not have a CAT so I'm wondering if the Eruo cars were set up differently? Anbody out there have a 1980 Euro? What type of rotor are you running?

John

I have a 1980 euro. The rev limiter is controlled by the CDI box, not the rotor.

-Rob
1980SC

John, I would say that is correct. I'm guessing since the Euro model year before yours may have had the big rotor, that somewhere alone the line the wrong one got changed into your 911.
The issue can be further confussed if you read the Haynes Manual. It states "European models have mechanical rev control. . ." If they would have said "Most European models have . . ." it would be helpful; and corrolate to Warrens info.
Anyway, I can see where the wrong rotor could be selected.

Rob (1980SC) info should help give you confidence. If your not sure you have correct year ignition, Waynes info implies (to me) that you can check to see if you hav the six-pin or 3-pin CD box; to answer you question.

Although, if it were me, I would test it. Change out the rotor and start creeping up on redline; second gear on the highway would be fairly tame.

Guys ...<b> the six-pin CDI-unit doesn't 'CONTROL' anything except the ignition transformer ... however it does generate a 'TD' signal for the tachometer, and that same signal is also used as the input to the 911.617.136.00 Speed Relay/Rev Limiter module, which in turn operates the fuel pump relay ... which removes power from the fuel pump ...</b>

Thanks for the info. I'm going to look for the speed relay/rev-limiting module tonight to see if it's there.

John

"911.617.136.00" Hmmm.

I went looking for mine. The Bentley manual did not say where the relay is located, but did give the ground location (mid dash). From there, I found this relay; (911 618 102 00) behind the gas gauge.
http://www.pelicanparts.com/ultimate...limitrelay.jpg

Traces 86 & 85 are the correct traces to controll the fuel pump; and I don't think I have a factory alarm. (The only other thing that would be controlling there.)
Did they change this in '81? or am I just looking at the wrong relay? . . .

Yep, wrong relay ... that is the seat belt relay!

Remember, it is connected to the tach 'TD' lead and the fuel pump relay, as in the following diagram:

<img src="http://www.pelicanparts.com/ultimate/image_uploads/82SCschematic-1s.jpg">

John,

The Bentley manual only covers USA-spec cars, so the info doesn't apply to your car!

Assuming that you have a type 930/09 engine, per the spec book, your rev-limiter rotor is what the ROW cars had, and that means you don't have to bother looking any further for the elusive relay/speed switch that ... along with a few dozen to few hundred other ommisions, Bentley left out of the manual ...

I really loved the shot of a '72/'73 MFI car's engine compartment that they chose to use/borrow to illustrate the location of an external Voltage regulator, too!!!

Well isn't that just great. I've been reving the piss out of my 930/09 engine while autocrossing, and I don't have any type of rev limiter. Where would the speed relay be if I did have one? Behind the guages? I looked all around for it, but found nothing.

So I guess I need a new rotor. I have a plain one. Is 6800 rpms correct? I know I've gone past that a few times!

Thanks alot for this info! I was sure I had an electronic rev limiter.

-Rob
1980SC euro

My car is a '79 Euro. When I got it 6 years ago it had a rev limiting rotor but I changed it and the only one available was the ordinary one. It definitely doesn't have any rev limiting now as I've had it around 7,000 alot.

Gulp, I guess I'm in the same boat, but I don't remember ever being north of 7000!

So where are we all going to get the correct rotors?

Bill. I think our favorite German, Roland, posted something some months back about part numbers. I think it was slightly different number for different rev cut off limits. Hey where is that guy! We haven't heard from him for a while.

Actually I reved my car north of 7,000 when I had the sterio up full blast (a bit to drink - bad boy) and was in fourth gear (thinking i was in 5th) at something like 110-120mph wondering why the car wouldn't go any faster.

The rotor that was on my car was a Bosch 1234 382 240 set @ 6800 rpms. A replacement should be here on soon. Thanks for all the help.

John