Increased spring rate; Edelbrock products offer improved performance and aesthetics for a broad array of vehicles and engines. 'Proven performance' is the philosophy by which Edelbrock was founded and it continues to this day with the highest standards for performance and quality. Edelbrock core products are engineered manufactured and tested in the USA to ensure the best quality possible. This is further backed by some of the best warranties in the industry and a highly qualified technical support staff.; Higher seat load for much better dynamic stability. Unique ovate spring wire to better manage operation stresses & create additional dynamic control to help valve train reliability at elevated RPM and boost pressures.