ZL1 Aluminum Big-Block - The Block That Rocked

Chevrolet's history is replete with the names of big-block engines that ruled the boulevards and the drag strips in the 1960s. All of them started with the letter "L," and were issued names like L78, L88, and L89. The most brutal of all was a limited-production, exotic powerplant that was produced for all-out drag racing. Its name was the ZL1.

The ZL1 was first born into competition when Jim Hall began using all aluminum 427 engines in his Chaparral Can-Am race cars. The phenomenal success of these road course engines caught the attention of Fred Gibb, a Chevrolet dealer in Kansas City, Missouri, and Dick Harrell, a talented Chevrolet drag racer who had hooked up with Gibb to build drag and street performance cars. They had already found how to make a lot of horsepower out of the Z/28, and were looking for new projects.

Chevrolet's central office had established a program permitting a dealer to place an order for a vehicle that was equipped with options not normally installed. In essence, if a certain mix of regular production options weren't offered on a particular model, then a central office production order (COPO) was submitted. If engineering approved the new mix of equipment, then a COPO number was issued, and the order for production was placed. In 1968, Gibb ordered 50 1968 L78 Novas under the COPO program with M40 Turbo Hydra-Matic automatic transmissions in place of the usual four-speed gearbox. It was the first time Chevrolet had ever placed an automatic transmission behind a solid-lifter engine. By building 50 of these, the Nova was qualified to race with an automatic, which Gibb and Harrell knew was badly needed, and could be more than competitive.

They chose to apply this same strategy to the 1969 Camaro. They were aware Chevrolet Engineering was planning to release what was basically an all-aluminum version of the 427-cid L88, however it would have open-chamber heads. The engine was designated ZL1, and had been planned for the Corvette.

To ensure reliability, the aluminum block received cast-iron sleeves, which were retained with a 1/16-inch grove at the top of the block. The main bearing bulkheads were beefed, and many of the bolt and stud threads throughout the engine were lengthened for greater strength. The forged steel rods were thicker in the caps and the shank base, with bigger 7/16-inch rod bolts. Along with the open-chamber design, the heads received bigger exhaust ports than the L88, they were round instead of square, and they boasted bigger 1.88-inch valves. That resulted in exhaust valve lift being increased to .600 inch, and the duration shortened to 359 degrees. The ZL1 was the first Chevrolet production use of the 850-cfm double-pumper Holley carburetor on an open-plenum, high-rise intake manifold. Chevrolet rated the ZL1 at 430 hp at 5,200 rpm, and 450 lb-ft at 4,400 rpm; however, dyno tests of factory ZL1s revealed its output was more in the 550hp range.

Chevrolet Engineering's Vince Piggins, Gibb, and Harrell developed the COPO package that would place the ZL1 in a Camaro to qualify it for the 1969 NHRA season. They knew the 150-lb weight savings of the ZL1 would make the Camaro competitive against the Hemi. Designated COPO 9560, the package started with an L78 Camaro replaced by the 427-cid ZL1 with cast-iron exhaust manifolds, 14x7-inch wheels, and F41 heavy-duty suspension that included heavy-duty springs with five-leaf rears. The ZL-2 cold air cowl induction hood was included, along with a heavy-duty radiator, transistorized ignition, power front disc brakes, radio delete, and F70x14 white lettered tires. The M40 automatic or the M20, M21, or M22 manual transmission with a special 15-lb nodular flywheel was offered. (The M22 was later deleted.) The 4.10:1 rear axle with heat-treated ring-and-pinion and posi-traction limited slip was the only rear available.