The River City Diesel 6.0L & 6.4L High Rev / High Pressure Valve Springs are the premium choice for diesel performance enthusiasts or competitors that continue to push the performance envelope. The heat treating and alloy choice is the latest available with the addition of chamfering, polishing, nano-penning, and other fatigue and load loss enhancements. The RCD team works very hard to ensure this technology is one step above the competition. When matched with the River City Diesel Custom Ground Camshaft you can expect a smooth power curve all the way up to 4,000 RPM.