[blykins]

I usually aim for the engine's horsepower + 10%. That way if the customer decides that he/she wants to hit it one time at the strip with drag radials or slicks, the clutch will hold.

You're right, as the clutch disc's coefficient of friction goes up, the possibility of clutch chatter goes up as well. However, the weight of a Cobra really helps out here (as does a lower rearend gear ratio) and I can usually match a Cobra up with a sintered iron clutch disc and not have any issues. Where I really have to watch my P's and Q's is when I spec a clutch for something like a Galaxie or Fairlane with a 3.00 gear.