Since its inception, the 427 cubic-inch Chevrolet big-block has become a legend for engine enthusiasts around the world. Whether it’s a small-block stroker or big-block powerhouse, chills seem to find their way up the neck of those lucky enough to have one in their ride.
The first of a three-part installment will be dedicated to the series of 427 cubic-inch engines that were so popular in the late-60s musclecar era. Part one will take a look back at the early L88 and ZL1 engines and compare them to the modern day ZZ427. In the coming months, part two will show how to build a modern day ZL1 using the aluminum block still available from Chevrolet Performance and aftermarket parts. Finally, part three will cover what goes into building a modern day ZZ427 using parts from Chevrolet Performance.
The Legendary L88
The L88 engine was introduced in 1967, and although it was only offered in production vehicles until 1969, its legacy has carried on for decades. Only the informed would have been impressed with a quick glance under the hood, however, each year brings about improvements, creating a legacy that has survived into modern times.
Although a forged-steel crankshaft with forged I-beam rods was used, the beam portion of the rod wasn’t quite up to the task of supporting nearly 500 horsepower for any length of time. A weak point was quickly identified, and it was cured the following year with a new, thicker connecting rod that included floating wrist pins and spiral-lock retainers. The 3/8-inch knurled shank rod bolts were also replaced with 7/16-inch smooth shanks.
The pistons were also forged. With the availability of high-octane leaded fuel, the compression ratio was higher than most street engines today. Static compression was calculated at 12.5:1 requiring at least a 103-octane fuel. The increased compression allowed the relatively short stroke of the 427 engine to produce plenty of torque.
The L88 used the same solid lifter camshaft profile for all three years. Duration was advertised as 326 degrees on the intake, while the exhaust breathed a bit longer at 334 degrees. Lift at the valve was .540 and .560-inches for the intake and exhaust respectively. The aggressive cam profile also required a third inner damper spring to control the valves at speeds up to 7,000 rpm. Rocker arms were stamped steel and required a longer slot for the L88’s high lift. Pushrods were also a hefty 7/16-inch diameter.
Aluminum cylinder heads reduced the 427 big-block’s overall weight by 70 pounds compared to the iron head versions. Closed combustion chambers were used with the first generation of L88 heads, and chamber size poured out at 106.8cc. Intake valves measured 2.19-inches and exhausts were 1.72-inches. Intake ports were a rectangular shape, and exhaust ports were squared-off to match up with the exhaust manifold.
In 1969 significant improvements were made for the aluminum cylinder head. Intake ports were reshaped, and material around the spark plug was removed, allowing for 30 percent more airflow. The pop-up piston was also reshaped with airflow in mind. As a result of the 118cc open chamber and reduced piston volume, compression was lowered to 12.0:1. However, the improved design still resulted in more power. The exhaust ports were also rounded to match tube headers, further extending its power capabilities.
A dual-plane aluminum intake manifold was used, and the carburetor pad accepted a standard four-barrel Holley. The divided-plenum under the carburetor was milled down to create an open chamber on the high-rise intake. In 1969, the divider was trimmed down even further to accompany the better flowing cylinder heads.
Only the intake manifold was left unpainted for the 1967 versions; the aluminum heads were covered in orange. Chrome valve covers were installed in 1968, and Chevy left the bare aluminum finish of the heads unpainted, making the engine a bit more aesthetically pleasing.
In order to compete in Production Class racing, the engine needed to be street legal from the factory. Although a PCV valve (Positive Crankshaft Ventilation) was widely used starting in 1963, the L88 utilized a road draft tube in 1967, which meant it could not be licensed in California. However, all vehicles, starting in 1968, were required to have a PCV system and a purified exhaust. As a result, even the high-performing L88s came with a belt-driven Air Injection Reaction (AIR) pump and PCV system. The government also mandated the installation of a heater and defroster on all street cars, requiring a heater hose connection on the intake manifold.
The Corvette was Chevrolet’s flagship performance car, and it was logical that the Bow Tie’s most powerful engine be featured in the Corvette. However, Zora Duntov previously argued that the early 348ci and 409ci engines would be detrimental to the car’s handling because of its weight. Nevertheless, big engines with big power dominated the 1960s, forcing the second generation of Corvette to be built with this in mind. The production of the aluminum head L88 in 1967 reduced the weight of the large displacement big-block to 610 pounds overall, but there were still pounds to shave.
While the heavy big-blocks were holding their own in the drag race scene and stock car racing, weight kept these powerhouses out of the Can-Am sports car series. For those guys, Chevrolet R&D had been supplying all aluminum 327 small-block racing engines to Chaparral cars in Midland, Texas, since 1963. When rumor hit that Ford was releasing an all-aluminum 427 for the 1968 season Vince Piggins and his product promotions group countered with an aluminum block 427 Chevrolet to be offered to the Can-Am competitors.
Piggins was able to see beyond the Can-Am scene, and also lobbied to bring the aluminum block to production cars. Excited to trim some pounds off the L88 for the Corvette, Duntov supported the idea 100 percent. Fred Frincke, casting designer for the L88 aluminum head, was now on the production engineering team and designed the aluminum production block. In 1969, the ZL1 engine was born.
A Fledgling Legend: The ZL1
In addition to the second design L88 cylinder head, 1969 was a big year for the “Rat” engine, as Chevrolet offered its first all-aluminum big-block for production cars. The ZL1 was a Regular Production Option (RPO) for the Corvette, and a Central Office Production Order (COPO) for Carmaros that were strictly intended for racing.
The now-coveted block was made of 356-T6 aluminum and produced at the Tonawanda foundry in New York. A programmable five-axis, omni-mill, machining center, shaped the aluminum castings into the final state. Thicker decks, bulkheads, and cylinder walls were utilized with additional core supports, gussets, and reinforcement webs for strength. Cylinder liners were needed, and were made of cast iron. These liners were frozen and then placed inside of a heated block. When both returned to room temperature, they wer inseparable. All of the primary dimensions of the ZL1 block matched its iron sibling.
The aluminum block did feature a main oil galley that was moved next to the camshaft and offered a provision for an external dry-sump system. The use of additional head bolts also carried over from the competition blocks to production units. Two threaded tabs protruded into the lifter valley from of each deck to provide extra clamping force.
Other than the block and camshaft, the ZL1 was identical to the L88. Both used the second design cylinder head that flowed 30 percent better than the first. The ZL1 capitalized on the extra airflow by utilizing a more aggressive camshaft. Intake valve lift was increased .020 inches to .560 inches, while the exhaust reached .600 inches. Intake duration was reduced to 322 degrees advertised duration; the exhaust duration was unchanged from the L88 camshaft. An aluminum timing gear with nylon coated teeth was attached to the camshaft and driven by an inverted tooth chain.
Conservative power ratings for the ZL1 were averaged at 525 horsepower. Installing a set of tube headers helped the peak number grow closer to 600 horsepower, but all that power came with a hefty price tag attached and added $4,718.35 to the bill, doubling the price of a Corvette coupe. Sticker shock surely contributed to the rarity of this nostalgic masterpiece. Government regulations required lower-octane fuel and consequently lower compression ratios. Chevrolet added a longer stroke to make up for the lost power, and in 1970 the 454ci engine replaced the L88 and ZL1 engines. The only year it was offered in a production car was 1969.
The L88 engine is one of the most popular big-block engines in Chevrolet’s history. While the aluminum-headed 427 was only offered in production vehicles between 1967 and 1969, its demand carried on for decades. Chevrolet Performance resurrected the 427 Rat from the grave, and packed in some modern goodies.
“The ZL1 and L88 were only produced for a couple of years and were designed to burn race fuel,” says Bill Martens, Chevrolet Performance special programs manager. “The modern-day ZZ427 has a pump-gas friendly 10.1:1 compression ratio, which makes this 427 streetable.”
The bore and stroke dimensions have changed slightly. A 4.250-inch bore is just a tick smaller than the ’60s version, while the stroke grew to 3.766 inches. Both the crankshaft and connecting rods are constructed of 4340 forged-steel, while the pistons are forged aluminum. The eight slugs have a smaller dome than the previous engines to reduce the compression ratio to 10.0:1, allowing the use of 92 octane pump gas. It still puts out a stout 480 horsepower.
The modern-day ZZ427 has a pump-gas friendly 10.1:1 compression, which makes this 427 streetable. – Bill Martens, Chevrolet Performance
While the ZZ427 uses an iron block and aluminum heads like its L88 predecessor, the new versions are quite different than the old school production. Cylinder head intake ports are a true oval shape, and valve size stayed the same as the second generation old school heads. But, ovate wire beehive springs are used in place of the triple-spring setup, allowing for better valve control with less pressure, heat, and wear on the springs. Also, the combustion chambers have shrunk to 110cc.
The Gen VI iron block has the main oil gallery next to the camshaft, just like the ZL1, and all five main caps benefit from the extra clamping force of four bolts. A one-piece rear main oil seal replaced the two-piece design of the 60s, and the front timing cover is a six-bolt design with an integral timing pointer designed to house a high-strength, single row timing chain. The ZZ lifter bores are longer with a machined boss on the top edge that accepts roller lifters with dog-bone style retainers. Finally, the deck surface of the ZZ has a modified, teardrop-shape coolant passage, making any head gasket designed for the Mark IV big-block incompatible.
Whether it’s the popular aluminum-headed L88, an ultra-rare aluminum block ZL1, or a modern day ZZ427, it is certain that the 427 has made an impression on the automotive enthusiast. Stay tuned for more as we cover what it takes to build one of these iconic big-blocks for yourself.