S65 engines have had broken valve springs issues. CarBahn with its enormous Race engine experience has produced High performance valves made with the same materials and process as their race engine valves springs. Thes valve springs have won 3 Prototype racing championships and two 24hr of Daytona overall victories. These are the highest quality valves springs available on the market.
Theory
The goal of a valve spring pressure is to make it as low as possible. This is because compressing a spring takes energy and robs potential power. In addition, more valve spring pressure increases valve train wear. We work very hard at running just enough valve spring pressure to keep the follower in contact with the camshaft but no more. If you increase the RPM you increase the valve spring just enough to manage the inertia from the increased RPM. The valve spring also needs enough seat pressure and the correct frequency not to bounce when the valve is closed. This is to avoid leaking trapped mass (the fuel air charge).