[Geo]

Here is some info I found online about the ZLX 427

The most famous version of the 427 was undoubtedly the 1969 ZL1 engine. Developed for Can-Am racing, where it was very successful, the ZL1 had specifications nearly identical to the production L88 version of the 427, but had an all-aluminum cylinder block that weighed 100 lb less than a similar iron block. The engine was also fitted with the new open combustion chamber cylinder heads, a lightweight aluminum water pump and a specially tuned aluminum intake manifold, resulting in an engine weighing little more than a small block, but producing around 600hp in "street" tune and far more in racing tune. The 4718 dollar cost of the ZL1 option doubled the price of the 1969 Corvette, but resulted in a car with exceptional performance. Just two production Corvettes (factory) and 69 Camaros (non-factory option COPO 9560) were built with the ZL1.

Chevrolet capitalized on the versatility of the 427 design by producing a wide variety of high performance, "over the counter" engine components (marketed as "heavy duty" or "extra capacity" components to mask their intended racing application), as well as ready-to-race "replacement" engines in shipping crates. Some of the components were developed to enhance the engine's reliability during high RPM operation, possibly justifying the use of the description "heavy duty." However, most of these items were racing parts originally designed for Can-Am competition that found their way on to dealers' shelves, and were meant to boost the engine's already impressive power output. As a result of this activity, the 427 quickly became dominant in drag racing.

The version of the 427 produced from 1966 to 1969 was fitted with essentially the same cylinder heads as used with the 396, a type often referred to as the closed combustion chamber design. Starting in 1969, the highest performance models were fitted with the new open chamber cylinder head, which along with design improvements in crankshafts, connecting rods and pistons adopted from the Can-Am development program, resulted in an engine with substantially increased performance and reliability. This development culminated in a specialty version of the engine called the ZLX, which was essentially a ZL1 engine built with the L88 engine's sturdy, four bolt main bearing iron block (it has been suggested that "ZLX" was a code name for ZL1 crossover). The ZLX, available as a short block assembly or complete "replacement" engine in the crate from a few dealers, was a resounding success and became a best-seller by after market racing components standards—the closest thing to an all-out competition engine ever offered to the general public. Chevrolet gave all 427 engines except the ZL1 a torque rating of 460 ft·lbf (624 N·m).