"ZL1" is perhaps the most coveted RPO code in the history of Chevrolet, and for good reason. Only two documented cases exist of '69 Corvettes being produced with this legendary all-aluminum 427. (A total of 69 ZL1 COPO Camaros were also assembled that year.) Even today, nothing gets the senses stirring like the thought of dropping the hammer on the most exotic big-block ever to roll out of a Chevy assembly plant.
What made the ZL1 so special? For starters, the engine represented the culmination of years of developmental work by GM, with more than a little race-bred testing and validation thrown in for good measure. By 1967, Chevy had rolled out the L88, a high-compression, solid-roller-filled, aluminum-headed race motor that somehow found its way onto the streets of America. The 427ci L88 continued to be available, both as an option in the Corvette and as a crate engine, through 1969, when the ZL1 made its debut.
By then, Chevy's burgeoning interest in Can-Am racing fostered a series of small tweaks to the 427 that added up to one major advancement. What separated the ZL1 most from its big-block predecessors was the use of an aluminum block, which knocked a whopping 100 pounds off the total weight of the engine. For race cars, lopping 100 pounds off the front could mean the difference between simply being competitive and dominating the competition.
The $4,718 ZL1 option brought a lot of race engine for the money. Of course, the aluminum ZL1 block was the top draw, but there was much more to the package. The L88's large-port aluminum heads were revised with an open-combustion-chamber design that yielded a 12.25:1 compression ratio. The intake was also aluminum and wore an 850-cfm Holley four-barrel.
Fitted with a high-lift, mechanical-roller cam, the ZL1 was rated at 430 horsepower at 5,200 rpm and 450 lb-ft of torque at 4,440 rpm-the same as the L88. Experts placed the ZL1's actual power at around 500 hp at 6,400 rpm, which seems much more in line with the radical nature of the cam. Add headers and an open exhaust, and the mighty aluminum big-block could belt out 550 to 575 horsepower. This was no mild-mannered street engine, however. The track-ready ZL1 demanded high-octane race fuel and judicious tuning. It started hard, idled rough, and ran like a scalded dog.
Over the years, the value of cars originally equipped with this alloy titan has skyrocketed. A ZL1 Camaro recently sold at auction for $840,000, and even clones are approaching the $200,000 mark. That puts the ZL1's unique blend of small-block weight and dump-truck torque outside the reach of all but the most deep-pocketed enthusiasts. So what about the rest of us?
Although GM Performance Parts has offered the ZL1's aluminum block (PN 12370850) for the past few years, nothing in the crate-engine realm has come close to matching the factory-built '69 ZL1...until now. Early in 2008, GMPP will release an all-aluminum 427-incher that holds true to the legend of the ZL1. Called the Anniversary 427 Big Block, it is part of an attempt by GM to bring back some of the products that helped launch its Performance Parts arm in 1967.
Based on the ZL1 block, the Anniversary 427 features a forged rotating assembly, oval-port big-block heads, and all the associated hardware you need to have a brand-new ZL1 right out of the box. The only deviations from the original are a hydraulic-roller cam and a 10.1:1 compression ratio, which together make for a pump-gas crate engine that will still pump out close to 500 horsepower.
This is a true collector's engine, with only 427 units to be produced. Each one will come with a leather-bound owner's kit that includes a certificate of authenticity, special vehicle badging, and further documentation of the engine's pedigree.
For those who can't handle the estimated $20,000 price of the Anniversary 427 Big Block, GMPP will also offer an iron-block version called the ZZ427. It features all of the same main components without the aluminum block, and should carry a price tag of around $15,000.
VETTE was lucky enough to be given access to photograph the assembly of one of the prototype Anniversary 427 crate engines. Follow along as we see what the modern version of the ZL1 looks like from the inside out.