The Critical Difference - Part 3

PRESSURE PLATES

There are two key issues for performance/racing pressure plates: Safety and Performance.

Safety

You only need to know one thing to determine the general safety of a pressure plate. It must have a ductile or malleable iron pressure ring.  Most replacement pressure plates are gray iron and subject to bursting at elevated RPM. (Read: EXPLODING at high rpm.)  If your parts supplier is not able to confirm his product is ductile iron and meets industry safety standards (SFI), STAY AWAY FROM THAT PART!  Ductile or malleable iron isrequired for SFI materials certification. It must meet 60,000 psi tensile, 40,000 psi yield, and 10% elongation specifications to pass SFI testing and assure you maximum safety.

We read some amazing posts detailing how a clutch explosion has cut some guy's Corvette in two and how upset he is about the damage to his car but he never says: Hey, that clutch could have killed me!  A person would have to be very lucky to walk away from such a catastrophe.  Make sure the pressure plate you use is not just a modified stock type unit! 

While we're on the subject, any vehicle with significant power increases should be equipped with a steel safety bellhousing.  Even if the pressure plate is SFI legal, it is possible a piece of clutch disc or a fastener could fly off the clutch and go through an aluminum bellhousing.

Performance

The pressure plate is the third element of the clutch system. (1 Flywheel, 2 Disc, 3  Pressure Plate.)  The most important issue for you is that the unit you are purchasing actually has the pressure increase you need for your application. If you look at the pressure plate listings under COMPONENTS on this website you will see the pressure ratings for RAM pressure plates. These listings are static pressures. That means this is the pressure load supplied at all times regardless of the engine rpm.

We see a lot of manufacturers advertising high pressures, but we don't see any published pressure specifications. We've pressure tested some of these products and found the pressures far below our standards. You cannot get increased clutch torque load capacity without a significant increase in static clamp pressure.  DO NOT PURCHASE A PRESSURE PLATE UNLESS THE SELLER CAN VERIFY THE PRESSURE IN TOTAL POUNDS OF CLAMP PRESSURE.

Another issue is the addition of centrifugal assist weights on diaphragm pressure plates. The theory is that the clamp pressure increases as the engine rpm increases, (More clamp pressure at high rpm.)  The problem with this is, the counterweights are, 1.) On too small a radius to produce much centrifugal force and 2). The angle of the lever is too low or flat to provide any significant leverage for the force produced. So, this arrangement does not produce any useful additional clamp until it reaches very, very high rpm.

In addition, these counterweights are typically used with a stock pressure clutch. No additional clamp pressure is provided at low rpm where it is needed most when the torque load on the clutch is highest. We won't go into torque/rpm thing in detail but you should know that as engine and driveline rpm increases, torque load on the clutch decreases. Additional clamp pressure, if any, is generated at the wrong end of the rpm range. RAM solves this problem by providing the high clamp pressure you need at low rpm.

RAM competition pressure plates are built from individual specialized components to our strict performance standards.  Each unit is assembled, adjusted, then balanced to 1/2 ounce inch or less (A very important feature lacking with most other performance clutch manufacturers.)

The Pressure Plate Buyer's Checklist

  • Make absolutely certain the pressure plate you are buying has a ductile iron pressure ring casting that meets SFI material test specifications.
  • Buy a pressure plate that has a published pressure specification.
  • Avoid centrifugal assisted pressure plates for street/strip cars.
  • Seriously consider a safety bellhousing if available for your vehicle.

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