Safe redline for 81SC engine?
 

Just wondering, what was the factory redline for the '81 SC 3.0? And how much higher can they rev safely if at all. I've installed one with an MSD box and need to select a rev limiter pill.

The factory limiter on my 82 is 6500 RPM ± 200.

There is some info on the factory setup here.

Tom

Thanks much, 6500 it is. ;)

BTW I am not a fan of fuel shut off type rev limiters because they in effect lean the engine out when it need fuel most. MSD's soft touch rev limiter works very well and in fact is used in drag-racing for starting line rev limiting which involves holding the engine at full throttle against a second limiter attached to a switch usually mounted on the gearshift. In my drag car I run three MSD limiters, one for burnout (5000rpm) one for the redline (8000rpm) and one that I change depending on track conditions for the starting line (typically 5000-6500rpm) I have never lost or damaged an engine due to over rev with and MSD rev limiter installed. I have however see several blown engines due to leaning out on the factory rev limiter and destroying the main bearings (Mustangs) so I wouldn't make it a habit to "test" the limiter.

On my '81 SC the redline starts at 6200. I've bouned it as high as 6500 once or twice but never higher than that.

Quiet Boom:

I have heard that if you have the 934 SC motor, that 9000 RPMs should be the redline limit.

Of course, only if you have the Weber MFI set-up with a carb and two plugs for each cylinder. SmileWavy

Serioulsy, I have been following your posts here and at the Rennlist and I wish you great luck in your 911 endeavors. Nice to have you around and I am sure there are many folks here interested in your past drag racing knowledge and its application to the P-car that we all love.

Personally, I have been trying to build a stop light bandit that can hold its own around the twisties . . . but in a "period" sort of way. :)

Good luck to you, sir!

Best,

Kurt

Pelicanhead, RLM, PCASDRM and E911SRM

Thanks for the kind words Kurt, although I never plan to make my 911 into a drag car I do plan on making it much faster than it was originally. Hmm stoplight bandit eh? Sounds like short gears and a 3.6 are in your future, with Webers of course for that "period" sort of look hehe. ;)

Kurt - you're not "trying", I would have said "succeeding"!

AQB - check Kurt's profile - he doesn't need a wimpy 3.6...

I have been assured by my engine builder that my SC valve train is ok for 7200rpm (the rest of the engine stuff isn't SC though).

LMAO, I just read Kurt's profile! Stoplight bandit huh, more light stoplight terror. Let's see a motor that flat out rocks, with a short-geared 915 in a light car, yup he succeeded. :D

HI ......I thought i knew my 911 motor history but now i'm not so sure....when you mention the 934 SC motor do you mean the 943 which is the 911 SCRS spec motor in two wheel drive form the 953 being the four wheel drive SCRS ....i believe the 934 to be a turbo motor.......incidentally my 140,000 mile SC happily screams to 7000rpm!!....haven't tried beyond as power drops around here

I have a 75 930 motor with MSD box. I have the 7000 rpm pill. I have hit the rev limiter 1 time.

I think C. Streit reved his SC motor to 9000 once ;) ... he stands the valves up on his desk now...

According to the factory spec book:

Max. permissible speed 7000 RPM

I put a bunch of track miles on an '80 SC engine with my Crane box set at 7000. No worries.

-zuff

hEY QUIET BOOM, CAN YOU POST SOME PICS? i HAVE AN 81 ALSO AND LIKE SOME COMPARISON. gOOD LUCK WITH IT.

See my pelican page ;)

I am very confident an SC could take the 7K redline... But depending on injection, cam, and mufflers there might not be any power up that high.

For a stock SC I like to shift at 6K since power peaks at around 5500.

Of course not everyone here is running stock, so YMMV.

My '82 SC pulls all the way to 7K without hesitation. It would probably go past that if my nerves and my wallet would let it! :eek: (no rev limiter rotor on mine)

But unless modified you are out of the power curve. It would be more optimal to shift sooner.

Take it to the drag strip and test shifting at different RPMs and I bet the best times will be with a lower than expected shift point.

But it is fun to wind up :)

I have 20/21 cams which make power all the way to 30,000 rpm as far as I know. My rev limiter kicks in at an indicated 7K rpm. I'm not sure whether my tach is accurate or not.

Incidentally, there is a tiny red line in the frame of my tach located at about 1,050 rpm. I wonder if this is some kind of calibration thing, like those tiny temperature numbers on the temp gauge.

Finally, I disagree with folks who believe fuel pump rev limiters are not as kind as ignition rev limiters. I'd rather stop giving fuel to a cylinder with spark, than stop giving spark to a cylinder that's pumping fuel. And '82 SC has the fuel cut-off type limiter, not the rotor type.

It a good thing too, I inadvertently found it just the other day.
Worked like a champ!

Sort of scare the h@ll out of ya the first time, doesn't it.