These springs are highly recommended for applications over 250rwkw , to help eliminate valve float. Valve float causes damage to valve stem seals and collets and retainers.
Upgraded valve springs allow for a much more free revving and powerful top end power curve. OEM valve springs have approx. 40-45 psi seat pressure, once for example 15 psi is added to this equation (which acts against the valve spring), approximately only 25-30 psi seat pressure is left. This is nowhere near enough to keep the valves closed at high rpms.