Chevrolet Small-Block V-8: the Little Engine That Still Can
By Paul Stenquist on August 19, 2011, 2:00 PM
A sketch of the original Chevrolet small-block V-8, built in 1955.
Chevrolet, marking its 100th anniversary this week with its sponsorship of metro Detroit's Woodward Dream Cruise, announced on Thursday that it would build the 100 millionth version of its small-block V-8 engine this year.
It is fitting that the automaker would celebrate this milestone during the festival, as the power plant will undoubtedly be found under the hoods of more cruising vehicles than any other engine, though not all of those Chevy-powered cars will be G.M. products.
The term small block refers to the engine's compact design, a groundbreaking attribute when it arrived in 1955. Ground-shaking, meanwhile, was its performance potential. While current versions of the engine have evolved significantly, they retain the basic geometry and continue to be stout performers.
A multitude of small blocks have come and gone, but among them, that 55 example and the unit used in the 2011 Corvette ZR1, known in series as the LS9, are more than just bookends to a rich history.
The 55 V-8 displaced 265 cubic inches and was available in two versions. The standard version, rated at 162 horsepower, had a two-barrel carburetor and single exhaust. An upgrade brought a four-barrel carburetor, dual exhaust and 180 horsepower, a significant increase from the 115 horsepower of Chevy's standard 6-cylinder engine from 1954 and not far behind the 250-horsepower output of Cadillac's V-8. More importantly, the Chevy engine was more modern, more compact and lighter than the Cadillac lump. The Chevy 265 was the second overhead-valve V-8 developed by Ed Cole, the G.M. engineer; the Cadillac was his first.
Efficient packaging was only part of what made the first small block resonate with enthusiasts. The engine was engineered with stud-mounted ball-and-socket rocker arms that were lighter than other designs. The intake and exhaust ports were large and straight, so the engine could breath deeply. The crankshaft stroke was short in comparison to other engines, so displacement was achieved with large cylinder bores. Those factors made the engine reliable, powerful and capable of operating at high r.p.m.
The LS9 6.2-liter supercharged V-8 that powers the Corvette ZR1, meanwhile, generates 638 horsepower and 604 pound-feet of torque. One of the world's top performers, the engine nevertheless relies on a configuration and pushrod valve train that hark back directly to its ancestor.
John Rydzewski, Chevrolet's assistant chief engineer for small-block engines, said in a telephone interview that the LS9's aluminum cylinder block is similar to the cast-iron block of the 265 in that it shares the same 4.4-inch bore centers, 90-degree configuration and compact packaging. It differs in that the original block ended just below the crank centerline, while the crankcase of recent small blocks extends well below the centerline to allow for additional rigidity. He added that the changes to the small-block design have been gradual and that no engine in the series was a clean-sheet redesign.
The Corvette ZR1's supercharged LS9 V-8.
The newer engine's aluminum cylinder heads resemble the cast iron heads of the 1955 265 in that two valves per cylinder are still arranged in a straight line, but the valves and ports are much wider and offer a more direct path for intake and exhaust. The combustion chambers have also been shaped by computers for optimum burn, the spark plug position has been greatly improved and the bolt pattern has been revised for better cylinder sealing. Same family tree, but generations removed.
Up top, the older engine's carburetor and oil-bath air cleaner intake system have yielded to a roots-type supercharger, port fuel injection and computerized control. The distributor is gone, having long ago been replaced by a position sensor on the crankshaft and computer-controlled timing adjustments.
The early engine was fitted with cast aluminum pistons and cast iron connecting rods, while the LS9 was built with forged aluminum pistons and forged titanium connecting rods. Other advanced features, like piston oil-spray cooling, titanium intake valves and hollow stem exhaust valves help it endure the beating administered by hyper horsepower.
So, what does the future hold for the venerable V-8?
"We are looking at direct fuel injection for future small blocks," said Mr. Rydzewski, "It's in the works. We'll be able to take advantage of increased horsepower and low-end torque, along with better fuel efficiency and reduced cold-start emissions.
In other words, though the small block is well into its 50s, it doesn't seem that retirement is on its horizon.