The General Motors Z11 option was a factory COPO production option in 1963, available for order in the 1963 Chevrolet Impala Sport Coupe that was developed for drag racers specifically. The package consisted of an all-aluminum 427 cubic inch (7.0L) engine, cowl-induction air intake system, and special aluminum body parts to be installed on the Impala chassis. The Z11 was based around the W-series 409 big-block and used a 3.650-inch crankshaft stroke to arrive at the final displacement. According to internal General Motors documents, 50 Z11 engines were built at the Tonawanda engine plant to fill the 50 cars produced at the Flint GM plant; they used a high-rise two-piece aluminum intake manifold and a pair of Carter AFB carburetors to feed the 13.5:1-compression big-block and produce 430 horsepower and 575 lb-ft torque.

With so few cars produced, one might imagine that the parts from those cars are worth a healthy ransom in the present-day market; as we see from this ebay listing offering a Z11-headed big-block, there’s no doubt about that. Even more impressive is the fact that the seller has the engine up for a Buy It Now price of $50,000, or substantially more than this C6 Z06 Corvette.

According to the seller, the engine currently displaces 540 cubic inches, made possible through the use of an aluminum block from World Castings, a Callies 4.250-inch-stroke Dragonslayer crankshaft, and a set of 6.385-inch Manley I-beam connecting rods topped with Ross pistons filling the 4.500-inch bore. With a Hogan sheetmetal intake manifold and a pair of Pro Systems Dominator carburetors on top, the engine made 869 horsepower and 696 lb-ft torque on the dyno – a substantial improvement over the factory-produced piece from the 60’s.

While it’s not a complete Z11 engine, it does wear a set of the Z11 heads and valve covers. Is it worth the asking price? What say you, EngineLabs readers?