** As Used by Australia's leading Workshops - your guarantee of performance and reliability ** These PRO SPRINGS suit the Nissan RB26 Twin Cam engine. 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. Once installed, a much more powerful and free revving top end power curve is possible. OEM valve springs have approx 40-45 psi seat pressure, once 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. FEATURES : New and Improved design Direct replacement for the OEM spring - straight drop in OEM retainers can be retained NITRIDE TREATED and shot peened Spring. 37.2mm - 85-90Lbs (26.1mm-215lbs) Premium quality - Quality Aussie made Drop in valve spring!