Zoom, Hayes, and some Ram clutches are very stiff. I have used a lot of clutches including full race clutches over the years. The "Super Hayes" where we mixed and matched a disc and a heavier clamp pressure plate to get the grab back in the late 80's and early 90's was by far the haviest clutch I ever used, but back in the day the friction materials were not what they are today. Also they did not use very many "semi-centrifugal" type weights to apply more force to the disk as rpms went up, so you had to have a really strong clamp force to hold through racing rpm.
Now? It's a different animal altogether with clutches like Exedy, Exedy Twin Disk, McLeod Twin RST and RXT (outstanding product, but pricey). Choose a clutch not just on name though, but precisely what you want it to do, and what you'll EVER want it to do over the life of the clutch. If you plan bolt ons you have to factor that in, and if you go with pressure to the motor you definitely have to be mindful of how much torque that motor will put out. Clutches are rated for FLYWHEEL torque. Horsepower is meaningless as it's the torque that the clutch has to hold.
Tim 2001 Mustang GT Bullitt #2199 (02199) Exedy Mach 400 Clutch, Ford Racing Billet Steel Flywheel
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