Rev limiting dizzy rotor

[SpeedracerIndy]

I am a little confused on which cars had these. I thought my car did, but apparantly it does not since I took it to 7200 today on a missed shift. Really scared me, and I didn't go above 4000 the rest of the way home. I would like to limit my rpms somehow due to the 915 being so sloppy. Is there any way to limit the rpms with a dizzy rotor? ROW 81

[HarryD]

Hello,

You should have a rev limiter but it will not help you if you miss a downshift. If it is on the dizzy, there is a "funky" mechanism that interupts the hi tension circuit on the rotor. If you pull your cap, the rotor will have more that just a strip of metal from the center electrode to the the plug wires (like you see on an american dizzy). That extra stuff is the rev limiter.

On a downshift, the engine will increase revs to meet the required speed regardless of it's ability to provide power. In other words, the wheels are turning the engine.

On the other hand, the rev limiter works by shutting off the fuel and/or ignition if you rev to high under acceleration. In other words, the engine is turning the wheels.

Did you car run ok after the missed shift? Any funny/new noises? Any smoke not previously apparent? Some of the other experts here can most likely tell you what to look for but if it was me, with the car parked I would slowly increase revs to see if things are ok.

[Peterfrans]

A rev limiting dizzy is not going to help you on a missed shift, it isnīt like some kind of engine brake. The only thing it does is cut the ignition above a preset rev limit.

Lets assume I drive at 100 kph in fifth , this would mean about 2700 rpm. At the same speed second would give 6600. It is not the engine driving the car, but the car driving the engine.

7200 should not be to bad, the engine should cope with that ( I take it to 7300 regularly, but thats a 70S). If the engine is running ok probably nothing happened. Best advice is to take the slop out of the shifter linkage or install an aftermarket shifter.

Good Luck

[SpeedracerIndy]

The missed shift was a missed up-shift. I went from first to second, and the car slipped out of second when I layed into the gas. My 915 has a tired 2nd gear syncro. Usually I am very careful when shifting into second, and go very slowly, but I got lazy. No engine problems since though. I deffinately do not have the rev limiting rotor you mentioned (just checked). Can they be purchased here on PParts? If not, where do you get them?

Also, I just ordered all new bushings the other day from PParts. I installed the factory short shift kit, but my car did not like it at all so I put the original back in. It would not shift into 5th or reverse not matter how much I adjusted the shift linkage. I have also heard that the factory short shift kit can acctually be harder on already worn out syncros, so I'll stick with the original. I does fine as long as I'm patient.

[HarryD]

Originally posted by CDiercks
The missed shift was a missed up-shift. I went from first to second, and the car slipped out of second when I layed into the gas. My 915 has a tired 2nd gear syncro. Usually I am very careful when shifting into second, and go very slowly, but I got lazy. No engine problems since though. I deffinately do not have the rev limiting rotor you mentioned (just checked). Can they be purchased here on PParts? If not, where do you get them?

Also, I just ordered all new bushings the other day from PParts. I installed the factory short shift kit, but my car did not like it at all so I put the original back in. It would not shift into 5th or reverse not matter how much I adjusted the shift linkage. I have also heard that the factory short shift kit can acctually be harder on already worn out syncros, so I'll stick with the original. I does fine as long as I'm patient.

OK, did you check by reving the casr up to the "cut off speed" or by looking at the rotor. Some cars limit revs in the CD Box and the rotor will look normal.

Try this test.
*Car in neutral
*Press accelerator gently to SLOWLY increase revs
*Things will get really loud, but look at tach.
* When you are at red line the engine should start sputtering.
*That will confirm you rev limiter is working.
* IF YOU GO WAY PAST REDLINE. STOP. Rev limiter is bad.

FWIW, when i did this test, the noise was unbearable and I was sure my engine would blow up. But when I hit 6600 rom, sputter .. sputter ... sputter... until I lifted. This also occasionally (not often enuf) happens at Autocross since I do not want to change gears for short high speed sections.

[HarryD]

Hi,

As an update, I saw this on Rennlist. Sounds like you have an electronic limiter that will not be a modified rotor.

>"Walter Fricke" wrote in message
news:746848@911...
>
>At some point the rev limiter on 911s was moved from a spring loaded
grounding contact in the rotor moved by inertia to a system >involving the
engine computer to sense engine RPM from a tach signal and send a signal to
the fuel pump relay, causing the relay to >open and the fuel to stop
flowing.

Sorry, jumping in late here (haven't been reading my digests), but this is
something I actually know something about.

I can tell you for sure the 1979 SCs (at least my US-spec car) had the
electronic rev limiter, because my car had it fail. I've never heard of
this happening to anyone else.

After I bought the car I found the rev limiter wire to the fuel pump relay
was cut. Yikes! I fixed it, and the car seemed to run fine at first. Then
after a few days the engine started to cut out intermittently. Before that
day was over, the engine quit completely. I had to cut the wire again to
get home.

The location of the rev limiter isn't mentioned in any of the manuals, and
it was a real chore to trace the wires from the fuse panel to find it. It's
screwed to the body behind the fuel gauge.

[SpeedracerIndy]

So does this apply to Euro models as well? I have tried reving the motor in the garage to 6500+ and there was no sputtering or sign of fuel cut off. I didn't want to go much higher than 6500 because I think that is where the rev limiter should be. I assume this means that I do not have a rev limiter and that if I did it would be in the dizzy rotor. I am going to try to find the correct on to go in my car by calling Pelican parts and buy it.

[1980SC]

The euro SC's use a 6800 rpm rev limiting rotor. You can get one from Vertex if Pelican doesn't have them.

My limiter doesn't kick in until my tach is buried at 7,000 rpms. Tach's often read a few hundred rpm too high.

Rob
1980sc euro

[Joeaksa]

Doubt that it would hurt to have the electronic limiter as well as the manual version in the rotor. Find out what was the limit for your particular motor and Pelican should have them.

Its cheap insurance...

Joe

[Jadams1]

Here's a helpful thread .

Engine over rev protection question?

[SpeedracerIndy]

Thank you, VERY helpfull thread. I just need to get the spec books so I can learn more about how to decipher the numbers on my car.

I hate to rehash this again, but... Am I correct in reading that if I have a 6-pin CD box, that the box electronically limits revs. AND/OR, since my car is Euro that doesn't apply and I have to use the limiting rotor. Pelican sells limiting rotors but it says they are for up to '77. Will this one work. I know the dizzy changed directions in 78 to ccw, so I would expect the rotor to have changed as well. I will check Vertex to see what they have listed, but would rather be able to support our host and buy it here.

[1980SC]

The CD box has never controlled the rev limit. The USA '78-'83 SC's have a rev limiting relay that cuts power to the fuel pump. This was in order to save the catalytic converter from raw fuel. You do not have this relay in your euro SC. You need a 3.0L rev limiting rotor (6800 rpms).

Do not buy a 2.7L rotor. They do not fit. You'll probably have to go through Vertex, as Pelican doesn't seem to stock them.

Rob
1980sc euro

[SpeedracerIndy]

OK, I'm straight now. That's what I thought. I am suprised how much conflicting information there is regarding US spec cars vs. Euro spec. These engines are much more different that I first thought.