Edelbrock Part #613669 is a Pro Port head that requires professional porting prior to use since the ports and chambers are deliberately undersize to permit a wide variety of end applications. The head has an 11? intake valve angle and is intended for high output, large cubic inch, 4.84? bore spacing (stock) big block Chevrolet racing engines. The 613669 employs a symmetrical port head architecture similar to the Pro Stock DRCE3. The head is treated with the HIP strengthening process, prior to machining, to insure the finest casting possible. This version has an extended flange which will likely require a new exhaust system or changes to a standard flange header. ? FEATURES: ? Port Entry Int. / Exh 2.52? x 2.15? / 1.84? x 1.50? ? Exhaust runner volume: 80cc ? Intake valve diameter: 2.600" ? Exhaust valve diameter: 1.94" ? Deck thickness: 5/8" ? Valve spring diameter: 1.30" ? Valve spring maximum lift: .680" ? Valve angle: 11? ? Exhaust port location: 0.125" Raised Port ? Spark plug fitment: 14mm x 3/4 reach, gasket seat ? Heli-coiled exhaust bolt holes ? Tipped entry oval intake port opening ? Unique cooling flow for better durability and consistency ? Intake manifold and valley cover plates available for regular and tall deck blocks ? Hot Isostatic Pressed (HIP process) for improved strength ? Effective internal oil drainage plus available external oil drains ? Versatile cooling system options for a variety of applications ? Seats installed with underside guide bores at .375?. .502? Guides are included but will not be installed.