There aren’t many engines that stay in production for 70 years. Even the venerable small block Chevy V8 only lasted 48 years before it was discontinued in America – although it is still made in Mexico 62 years after its introduction. But the basic Chevy overhead valve inline six-cylinder engine was first introduced in 1929 and remained in active production until 2001, for a total production run of 72 years.
The Chevrolet straight six was introduced for the 1929 model year as the brand’s only power plant, replacing the 2.8-liter four-cylinder engine that powered earlier Chevs.
This pushrod six-cylinder design was only engine offered by Chevrolet from 1929 until the advent of the small block V8 in 1955.
First a Stovebolt Six
The earliest of these engines were known as “stovebolt” sixes, because the bolts that held the engine together resembled the bolts that were commonly used to assemble woodstoves. The new 1929 engine displaced 3.2-liters (194 cubic inches) and made 50 horsepower. While lubrication for the connecting rod bearings was by the traditional “splash” method of dragging the crank through the oil in the pan, the engine offered pressurized lubrication for the three main bearings, and a pushrod-actuated overhead valve design. Compression was low, at 5:1, and the cast-iron pistons were of course quite heavy.
The original stovebolt engine was produced until 1936, with a 1932 update to 60 horsepower, and a revised version introduced for 1934 that raised the horsepower to 80 from a 3.4-liter (207 cubic inch) displacement.
The Blue Flame Era
In 1937, the six-cylinder engine that came to be known as the “Blue Flame” was adopted. This plant was even bigger, at 3.5 liters (216.5 cubic inches) and 6.5:1 compression, yielding 85 horsepower. An additional pressurized main bearing was added, making the engine more reliable with four mains, and oil squirters to lubricate the connecting rod bearings. Compression increases in 1941 pushed output to 90 horsepower, and then to 92 horsepower in 1949.
The 1941 heavy truck modification to this engine series boosted displacement to 3.9-liters (235 cubic inches) and power to 123 horsepower in the Thrift-King equipped with solid lifters. The same engine achieved 136 horsepower with hydraulic lifters.
The final modifications to the Blue Flame generation came in 1954, with the fully pressurized Thriftmaster and the larger Jobmaster truck engine. The Thriftmaster made 140 horsepower, and is among the most highly regarded of the straight-six engines for its durability. The Jobmaster variant displaced 4.3 liters or 261 cubic inches, and developed 148 horsepower.
A Modern Engine
The final generation based on the 1929 design was first installed in 1962. This was almost a complete redesign, with 7 main bearings, all bearing surfaces pressurized, and it was designed to share parts with the small block V8 engine. The result, however, was durable and economical and continued to be used in new American passenger cars until 1979 and in trucks through 1988. This is the engine that was produced and used until 2001 in Brazil.
This final generation was produced in 2.9-liter (194 cubic inch) and 3.8-liter (230 cubic inch) variants. A single overhead cam variant was developed for Pontiac vehicles, and that engine made up to 215 horsepower. In 1975, displacement was bumped again to 4.1-liters (250 cubic inches) and 155 horsepower.
The Blue Flame Six and the Corvette
When the first Corvette was brought out in 1953, it carried a special version of the Blue Flame engine. The Corvette power plant was a 235 cubic inch engine with the 261 truck camshaft, which offered higher lift than normal 235 engines received. Induction was by three single-throat sidedraft Carter carburetors. The result was still a pretty tame 150 horsepower, delivered to the rear wheels through a two-speed automatic transmission.
The Corvette was offered only with the Blue Flame Six in 1953 and 1954. In 1955 the small block V8 and the Blue Flame were offered, but the small block could be ordered with a 3-speed manual transmission. Then Zora Arkus-Duntov got ahold of the Corvette, and that’s a whole story on its own.
Chevrolet’s Most Significant Engine?
The long-standing Chevrolet straight-6 engine was eventually phased out in favor of the Vortec V6, but millions upon millions of GM vehicles around the world were powered by this design for decades. No one knows for sure, but probably millions of these engines remain in service today. From Australia to South Africa and South America, the Chevrolet straight-six engine has been prized for its longevity and willingness to work.
The Small Block V8 gets a lot of well-deserved glory, and for versatility and power modifications that engine has no equal. But if you look at sales figures through the 1950s, 1960s, and 1970s, you’ll see that for every car ordered with a V8, Chevrolet sold three, five, even ten vehicles powered by the straight six. If the V8 is a race horse, the ancient Stovebolt Six was Chevrolet’s workhorse of the 20th century.