OEM valve springs have approx 50 psi seat pressure, once 15 psi is added to this equation (which acts against the valve spring), approximately only 35 psi seat pressure is left. This is nowhere near enough to keep the valves shut at high rpms 85-90 psi installed height of the new springs, some 75% more stiffness Highly recommend for 320+rwkW applications Pulled off the plazmaman site .