Maximum competition, competition/modified drag racing, circle track. Desert/endurance racing, Over 7,000 RPM, high compression low dome. Dart 9 Deg c-core heads offer the maximum performance for cylinder head porters and machine shops with CNC capability. These are the ultimate castings for head porters. The redesigned casting has been optimized for CNC porting. Features include: raised intake and exhaust port locations, optimized spark plug locations, optimized deck thickness, expanded water jacket capacity, bosses for down nozzles and revised valve cover rail to clear long ratio rocker geometry. Provisions for extra head bolts have been added to each end, making for an improved seal. Available in standard 4.400 in. or 4.500 in. spread bore spacing. It is recommended that you contact a Dart technical representative before placing an order for this item. Detailed information about your planned engine build will help to ensure that you choose the right configuration for your motor and that any special parts and considerations are taken into account.