The S2000  has been known for dropping valves, this is caused from the Valve Retainers cracking over time of high-revving or induced over-rev. This kit is the AP2 retainers & keepers which is of much stronger quality and almost bulletproof! This is a cheap insurance for our high-revving engines!Kit includes : (8) OEM Honda AP2 Upgraded Retainers
(16) OEM Honda AP2 Retainer Keepers (2 per valve)

This kit contains the required quantity for the intake valves, which are more prone to cracking.
If you want to upgrade both intake and exhaust valves, you will need to select 2 units.