72-89 225mm Pressure Plate clamping force

[Fixer]

I haven't been able to find data on the standard 225 mm 911 cast iron Sachs pressure plate.

I'm curious to know its clamping force rating as I have a new one on the shelf.

I've searched here and all over but no lb-ft figures.

Anyone know an exact spec?

Thanks

Matt 🇺🇲

[Jon B]

Originally Posted by Fixer

I've searched here and all over but no lb-ft figures.

Matt, it wouldn't be listed in lb-ft, that's rotational force.
The 74 factory spec was 715-785 kp (kilopond), which equates to 1575-1730 lbf (pound-force).

[stownsen914]

Maybe you're looking for break-away torque? (Essentially, how much torque will it hold before slipping.)

[manbridge 74]

They changed the spec over the years. Above is for 1975.

[Walt Fricke]

The 78-81 SC spec is 775-866 kp. Probably means all the 915 transmission era PPs have basically the same clamping pressure. The spring rate depends on the diaphragm spring - the 2.8RSR had a higher pressure, achieved by using a different spring. As or 20 or so years ago you could purchase these springs separately from Sachs in Germany.

[Fixer]

Originally Posted by stownsen914

Maybe you're looking for break-away torque? (Essentially, how much torque will it hold before slipping.)

Yes, this is what I'm curious about.

Thanks for the replies above.

[stownsen914]

I recall that people have put "built" 911 race engines making 300 hp in front of the aluminum "sport" Sachs 225mm pressure plate. So probably low to mid 200's lb-ft of torque. Maybe it's good for 250? Someone here will have better info. I'm sure. I recall that the 225mm RSR version is good for 350.

[Fixer]

Originally Posted by Walt Fricke

The 78-81 SC spec is 775-866 kp. Probably means all the 915 transmission era PPs have basically the same clamping pressure. The spring rate depends on the diaphragm spring - the 2.8RSR had a higher pressure, achieved by using a different spring. As or 20 or so years ago you could purchase these springs separately from Sachs in Germany.

Thank you Walt!

[Fixer]

Originally Posted by manbridge 74

They changed the spec over the years. Above is for 1975.

Thank you for this.

So 800 kilopond to pound force is about 1775 lbs of force against the disc. That seems significant but I'm guessing these plates weren't over built and the likely break away torque value (motor) is in the maybe mid 200s (lb ft)

A way to compare the potential grip of the stock Sachs 225 mm unit would be to find an aftermarket pressure plate where Kp is listed along with motor torque it will withstand.

A better clutch disc than stock would improve grip too.