Drop-in spec, that works with factory valve springs. Perfect for Duning with minimal mods and good gains in the mid-range. For trails, delivers excellent throttle response out of the turns and thru the wash, still pulls hard on the top end. Best results on RR or larger turbo setup, requires ECU tune and 1300cc injectors for optimal gains. Now includes crank locking tool (#529036272) to insure proper installation.