voodoo51

I have bought MSD ignition module. But don't know which rpm limit should I set.
My 930 is a daily driver (rare track days).

Thank you.
Sergey.

pu911rsr

I'd set it at the factory redline if motor has stock internals
Phil

mel_t_vin

Phil, do all 3.3L cars have the same redline...6800?

The factory rev-limiter is CDI-based, correct? Do you know at what RPM the CDI pulls ignition? 7100? 7150? I've spun my [warm] motor to 7000 many, many, times and have yet to trip the factory fail safe.

Just curious...

puddy

I thought these cars had a higher redline, 7200 or more. I often shift my hotrod at the track around 7000.

pu911rsr

I would not routinely spin a 74.4 stroke motor much beyond stock redline w/o doing a bunching of oiling mods to case.
Phil

voodoo51

We set rpm limit on 7000

strudel

If your going to track it, I would get it dynoed to see where the torque & power band are. On my 3.5 twin plug street motor peek torque is at 5,000 rpm, and peek h.p. Is at 5,500. While I can take it to 6800 rpm, I don't see any benefit shifting there. Just my .02.

Last930

I thought the rotor in the distributor had some sort of spring setup that cut the ignition once a certain rpm was hit?

Porsche 930

Per Porsche Workshop Manual 911 turbo;

IGNITION SYSTEM FROM 1978 MODELS
"Speed governor (in distributor rotor) 7000 +/- 200 RPM"

mel_t_vin

Would you happen to know if this 7000 +/-200 limit applies to all subsequent years, as well?

Porsche 930

Per the Porsche Katalog, rotor p/n 930 602 901 01 is used on all 930's from '75-'89, EXCEPT, on the US 930.68 motors of '86-'89, which use rotor p/n 930 602 902 00.

The 901 01 rotor used in my '79 has the built-in speed governor. I'm not familiar with the 902 00 rotor so I can't say if it has the governor or not.

mel_t_vin

Okay, thanks.

Out of curiosity, how does the speed governor function on the 901 01 rotor?

Porsche 930

The speed governor function is built into the 901 01 rotor and actually is pretty simple. As engine RPM increases the distributor rotor spins faster and faster until centrifugal force overcomes spring tension on a metal contact that shorts out the ignition. That's why, when you hit the rev limit ("Speed governor"), it feels like you've lost half of your spark plugs and your timing's gone all to hell. It is in effect, shutting the engine down from higher RPM's.
.

pu911rsr

Well the bad thing about tripping the rotor based RPM cut off is you loose spark but not fuel and you spray a bunch of gas into the cylinders that doesn't burn right away.

Phil

mel_t_vin

Thanks for that tidbit.

Phil, would you happen to know if the later, '86-'89, cars employ a similar ignition-based rev-limiter? Or?