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Let’s face it, in today’s world an inline-eight-cylinder engine is an anachronism. Modern vehicle design and technology lends itself to compact, lightweight, highly efficient engine designs. The straight-eight comes from a time when a long, narrow powerplant was considered graceful, and the inline eight-cylinder engine was a powerhouse that hadn’t been knocked off the mantle by V8 engines yet.
However, back in the inline-8’s heyday — the first half of the 20th century — the straight-8 was a king. Its even firing order made it a smooth performer, which made it popular in high-end luxury cars of the day. The fact that it made significantly more power than its inline six-cylinder competitors of the day also made it a popular performance engine option for racing of all types of the time period.
While time and technology have rendered the inline-eight-cylinder engine configuration largely obsolete, there is no denying the impact it made in automotive performance and design. So with that, we’ll look at four of the more interesting straight-8 engines from the eight (no pun intended) in the video above.
The Mercedes-Benz W196 engine came to be as a result of a new rules package for Formula 1 in 1954, allowing naturally aspirated engines of up to 2.5 liters, and heavily restricting the size of the supercharged entries, which Mercedes was known for. By taking the mechanical direct injection system they developed on the DB 601 engine (The inverted V12 from the Me-109 fighter plane), and pairing it with a desmodromic valvetrain, the W196 engine was born.
With a 2.992-inch (76mm) bore and 2.709-inch (68.8) to achieve its 2.496-liter displacement, it created 257 horsepower initially, which was less than the projected needs of the series. After developing a variable-length intake runner system, the engine achieved the 340 horsepower at 10,000 rpm performance target set out by the engineers. The mechanical direct injection system was a large advantage for the team, and the engine’s performance led the field, taking two championships in as many years of being fielded.
Suggested reading:The Packard Straight-8 engine is on this list, as it is the last American production inline eight-cylinder engine. It also has the distinction of having a thirty-year production run, with the first production model debuting in 1924 and the final straight-eight-powered Packard rolling off the line in 1954. There were a multitude of variants, ranging from a 257 cubic-inch variant with a 3.250-inch bore and 3.875-inch stroke making 203 horsepower, all the way up to the 384 cubic-inch behemoth with a 3.500-inch bore and monster 5.00-inch stroke, that made an underwhelming 109 horsepower at 3,200 rpm.
However, the later models were a 327 cubic-inch, 185 horsepower variant, and a 359-cube, 212 horsepower version, both of which sung like well-oiled sewing machines at full song. While the Packard straight-eight was eventually replaced by V8, it wasn’t in time to save the company, and the engine design’s retirement from production lines was overshadowed by the failure of its longest-running proponent.
Before World War II, Alfa Romeo debuted a new racing engine that displaced 1.5 liters and had 8 cylinders, creating the “158” moniker. The undersquare engine featured a 58mm (2.283-inch) bore and 70mm (2.756-inch) stroke, and with the help of a single-stage Roots-style supercharger, made 200 horsepower at 7,000 rpm. Once the war ended, racing development resumed, with the 1946 configuration peaking at 254 horsepower. The 1947 version was further refined to create 300 horsepower which carried it through the 1950 peak of 350 horsepower at 8,500 rpm.
For the 1951 season, the 159 variant was produced with a new two-stage supercharger system, which produced a significant increase to 425 horsepower at 9,300 rpm. Unfortunately, unable to secure additional development funding, the last time the 159 saw the racetrack was in 1953.
Saving the most powerful for last on our list, the Mercedes Benz M125 engine was designed specifically to power the maker’s 1937 W125 Grand Prix car development. It was designed around a rules package that didn’t regulate engine size, Mercedes decided on an undersquare straight-eight with a 94mm (3.700-inch) bore and a 102mm (4.016-inch) stroke for a total displacement of 5.66 liters (345 cubic inches).
On top of the stout displacement, the dual overhead camshaft engine was supercharged with a Roots-type blower. Using an interesting fuel mixture containing methanol, benzene, ethanol, and gasoline, the engine produced a peak output during it’s service of 637 horsepower at 5,800 rpm and as much as 632 lb-ft of torque. After being quite successful in its first year of competition, the engine was made obsolete the next season, thanks to displacement limits being put into place.
While these are only four of the eight engines covered in the video above, they prove that even though the straight-eight is considered obsolete these days, at one point in time they were the pinnacle of automotive performance, balancing weight and power in the sleek long-nose chassis of the day.
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