Ram’s 6.25in Racing Clutch Disc

It’s easy to underestimate the potential of a 6.25in racing clutch disc. After all it is tiny yet it transmits the power of 500cu in NHRA Pro Stock race cars, 400cu in Australian Pro Stockers, as well as 900 to 1,200hp Competition Eliminator cars.

   In fact this clutch is suitable for any powerful naturally aspirated small-block with a manual transmission and where some clutch slippage is desirable on initial take-off. Usually, the clutch assemblies for the 500 and 400cu in engines contain three discs while the Comp Eliminator contains two.
   This new clutch disc comprises a core plate with friction material at its perimeter and a splined hub at its center. Ram provides the specifications of their 5191 friction material to Raybestos who sinters it on the 1/16in thick core plate at 1,700 to 1,800 degrees Fahrenheit for over two hours. The core plate has four slots to prevent its distortion during the bonding process and also during operation. When trued the new friction surface is approximately .320in thick and 1in wide.
   From heat treated 4140 high tensile alloy steel, Ram constructs the splined hub and fastens it to the core plate with eight 1/4in stainless steel rivets. The hub usually features 10 splines to accommodate Liberty or G-Force transmissions.
   The friction material 5191 is renowned for its excellent wear characteristics—it is gentle on the mating surfaces. After each race pass a diamond-tipped dressing tool is used to de-glaze the surface of the disc and to true it, resulting in a very efficient friction surface. With careful re-surfacing a disc can complete 10 to 12 race passes.
   Ram recommends running the discs in varying stages of wear: one new, one with some wear, and one with substantial wear, replacing them one at a time. By rotating them in this fashion the assembled height of the clutch pack doesn’t vary too much, and the setup remains close to optimum. Typically these sintered discs are replaced when their thickness diminishes to around .250in.
   For further information on these 6.25in discs and related clutch assemblies as well as others, contact RAM Clutches at (803) 788-6034 or visit www.ramclutches.com.