S&S cams are tested on the dyno, street and racetrack before being offered to the public. With hundreds of test hours on them, you know that you are getting the best cam S&S can produce. For 84" to 93" motors, not more than 9:1. Best response occurs in the mid range from 2500 to 5000 rpm. Recommend high-performance hydraulic or solid lifters. Made in the USA. Spring spacing is required. Installer must check coil bind, valve-to-valve clearance, valve-to-piston clearance and cam lobe to case clearance..