The "Red Stripe" spring is the strongest 10.8 lb spring on the market and thus rightfully named Heavy Duty. The Heavy Duty clone spring will allow the engine builder to custom fit their spring kits. Having been through a specific process, which will reduce the amount of spring pressure loss from running in the engine, this spring will allow the engine to run a higher RPM before experiencing uncontrolled valve float.
This spring will not test legal without being set. Springs should be checked prior to installation to insure they meet rule requirements. Sold Each