GM Big Block V8 Engine; 8.1L/ 496 Cubic Inch; Automotive; 561 Horsepower/ 512 Foot Pounds of Torque; Cast Iron Block/ Aluminum Cylinder Heads; 8.8:1 Compression Ratio; 4.5 Inch Bore/ 4.25 Inch Stroke; Internally Balanced; With Cylinder Heads/ Forged Steel Crankshaft/ Forged Pistons/ Hydraulic Roller Camshaft/ 4 Bolt Main Block/ 1 Piece Rear Main Seal/ 6.135 Inch Forged H-beam Connecting Rods/ Valve Covers/ Oil Pan/ Timing Cover/ Power Adder Engine/ Dual Keyway Crank/ SFI Harmonic Balancer