Due to the aggressive nature of the camshafts, their high lift and the RPM I wanted the engine to reach, an upgrade to the valve springs was required. The new race springs will allow for all this. There were two options available: use a spring that would allow the std spring retainers to be used but require quite a bit of shimming or have new retainers made to suit a different spring & collet that required less shimming.
As we are in unknown territory with this engine, the suitability of the standard spring retainers for high RPM usage was in question. I made the decision to play it safe have custom EN16T steel retainers made. They also have the advantage of being lighter, as are the springs. Getting the valve train and reciprocating assembly as light as is feasible is important for releasing every ounce of power!