...with our kit you get a CUSTOM VALVE SPRING designed specifically for the Evo. This spring will allow you to run much higher revs and up to 14.0+mm of lift Our retainers are 100% chrome moly steel ( SUPER durable ) and only fit with our springs. I know what you're thinking.... "Steel??? why not Ti ??" Well after getting samples machined in Ti and weighing other Ti retainers out there we found them to be heavier than the OEM aluminum retainers. So we took a different approach - since we design our own springs we were able to design a "package" that has less unsprung weight than ANY other spring /retainer combo available. As we learned with suspension unsprung weight is the enemy of all things performance! Think of how many times, and how quickly a retainer and spring changes direction - its STAGGERING! At Revolver we can calculate just how much of the springs mass is unsprung. So while others might have a lighter retainer than ours but a bulky, poorly designed spring ruins it as a package. So with the Revolver spring/retainer combo you get the durability that you need in a daily driven street car with the lightweight rotating mass of a racing valvetrain.