N13/277 4V N13 Intake .501″ lift, 246° @ .050″ lift. 277 Exhaust .478″ lift, 236° @ .050″ lift. More lift and duration than 277/N11. S, S2, 968 cores must be welded. Race valve springs and valves required. Peak power at or near 8000 rpm. Customer must supply cores or we must make steel billets. Call for price.