Manual Trans Advice- the Importance of Matching Your Clutch To Your Application...

Like I said before, a clutch rating is just a quick/dirty way for the typical aftermarket clutch buying customer to feel assured that the clutch they buy isn't going to slip against the torque their engine is capable of. From the perspective of the aftermarket clutch manufacturer, if the clutch breaks something else downstream it's not their problem, at least the customer won't come back complaining about a weak clutch.

The typical aftermarket GM/Mopar pattern 10.5" diaphragm PP installed out of the box has about 2800lbs of clamp. Hard to find anything less in the aftermarket....
...With an organic disc, 2800lbs is ballpark for an engine with around 500ftlbs of torque.
...With a typical dual friction disc, 2800lbs is ballpark for an engine with around 775ftlbs of torque.
...With a ceramic puck disc, 2800lbs is ballpark for an engine with around 850ftlbs of torque.
...With an iron puck disc, 2800lbs is ballpark for an engine with around 825ftlbs of torque.

But what if your engine puts out something other than 500, 775, 825, or 850ftlbs? You could calculate a percentage of the above numbers to get you in the ballpark.

Say your engine puts out 600ftlbs, how much clamp would you then need for a typical dual friction disc? The above says 2800lbs of clamp on a dual friction disc is ballpark for 775ftlbs. If you divide 600 by 775, you get .77 which means you would need 77% of 2800lbs or 2800 x .77 = 2156. In other words a 600ftlb engine needs about 2156lbs of ballpark clamp on a 10.5" dual friction disc. Good luck finding that in the aftermarket.

Ideally though you are not looking for a clamp number, you are looking for a clutch that has just enough clamp to pull the engine down in about 1/2 a second after a WOT shift into high gear. The amount of clamp required to actually do that will vary with gearing and rotating assy weight, easiest way to adjust clamp pressure for the application is to use a Long style pressure plate that has adjustable static pressure. For example, Ram sells several versions of a basic non-CW 11" stamped steel Long with different ranges of adjustment...
#435 is adjustable between 1200-1800lbs
#448 is adjustable between 1500-2100lbs
#438 is adjustable between 1800-2400lbs
#458 is adjustable between 2200-2800lbs

All that said, I make devices that can momentarily soften the hit of any clutch. This enables your existing overkill clutch to initially hit like a much softer unit without giving up any of it's holding power. Also allows a clutch that is in the ballpark to work even better. It's a hard fact of stick shift drag racing that your clutch needs to slip more during launch than it does after the shifts.

Grant