S&S Super Stock Cylinder Heads For Harley Evolution Big Twin S&S heads deliver excellent performance and accommodate additional upgrades seamlessly. This kit comes fully assembled, featuring stainless steel valves and high-lift springs capable of lifts up to .640. Features: Available in natural and black powder-coat finish Fully assembled, and include stainless steel valves and high-lift springs (up to .640 lift) Compatible with stock 3-1/2 or 3-5/8 bore engines Large 2.000 intake and 1.605 exhaust valves and high flowing ports supply plenty of air for big inch engines S&S Super Stock 10:1 ratio piston kits are required and sold separately Intake manifold, pistons and gasket kits are sold separately Must reuse stock headbolts Made in the USA Sold in pairs