Everyone will prob give you a different answer. It depends on the rpm power band of your engine, and gearing as well as simple driver preference. I always set the clutch to engage just before the rpm band where my engines start pulling hard and building big hp. If set too high, you will just break the tires loose. I use 2800-3400 engagement springs in singles and anywhere from 3,200- 4000 in the twins, depending on the engine and track.