page_title: Straight-six engine
section_title: United States
hierarchical_section_title: Straight-six engine / History / United States
caption_attribution_description: 1954 Hudson Wasp flat head six engine
context_page_description: The straight-six engine is an internal combustion engine, with six cylinders mounted in a straight line along the crankcase with all the pistons driving a common crankshaft.
  The bank of cylinders may be oriented at any angle, and where the bank is inclined away from the vertical, the engine is sometimes called a slant-six. The straight-six layout is the simplest engine layout that possesses both primary and secondary mechanical engine balance, resulting in much less vibration than engines with fewer cylinders.
context_section_description: Engines of this type were popular before World War II in mid-range cars. Most manufacturers started building straight-six engines when cars grew too large for the inline-four engine. One of the longest-in-production inline-six automotive engines in the United States was the Chevrolet Straight-6 engine, which replaced Chevy's previous inline-four engine in 1929, and remained in continuous use in the US for powering Chevy vehicles until 1990, in displacements ranging from 3.2 liters (170 cu. in.) to 4.8 liters (292 cu. in.).
  After World War II, larger cars required larger engines, and buyers of larger cars tended to prefer V8s; performance sixes such as the Hudson Hornet 308 cu in (5.0 L) engine were exceptions to the rule, and were not often top sellers although it became one of the hottest cars on the road and dominated stock car racing (NASCAR) in the early 1950s.
  After Chevrolet introduced its V8 in 1955, the straight-six became almost exclusively a base engine model pitched to economy-minded customers. Trucks (both light and heavy duty) also incorporated the straight-six until the mid-1950s, and they are still used in light trucks available today. The new wave of compact cars that started in the late 1950s provided a suitable home for straight-six designs.
  The Chrysler Slant-6 engines used in the Plymouth Valiant and Dodge Dart A-body models of the 1960s and 1970s featured a 30° inclined design to achieve a lower overall height. Originally designed to be built of aluminum, but after encountering problems in manufacturing the engines in aluminum, they were built in cast iron without changing the design to compensate for the stronger metal. Although it only had four crankshaft main bearings instead of the seven used by its competitors, they were the same size as those on the 426 cu in (7.0 L) Hemi V8. The Slant-6 achieved some success in racing when engineers utilized the slant of the engine for very long intake manifold passages to boost horsepower by tuning the intake system. After 30 years of production, it was discontinued in favor of V6 engines because it was too long to mount transversely in front-wheel-drive cars.
  Kaiser Jeep introduced the Tornado straight-6 for 1963. It was the first U.S. designed mass-produced overhead cam (OHC) automobile engine. It was robust and built for heavy-duty performance, as well as featuring the lowest specific fuel consumption of all production gasoline engines in the market at the time. However, it was complex (by 1960s standards) for civilian vehicles in the U.S., but continued to be installed in military Jeeps and was also produced through 1982 by IKA in Argentina.
  A "modern era" straight-six engine family was introduced by American Motors (AMC) in 1964. These lighter in weight engines were used in a variety of AMC passenger and Jeep utility vehicles. American Motors also sold their straight-sixes to International Harvester for powering International's "Light Line" of trucks: Scouts, pickups, and Travelalls. These engines were also assembled and marketed internationally. Some markets (such as Vehiculos Automotores Mexicanos [VAM] in Mexico) built their own specialized versions. This engine is considered to be one of the best ever made, and it received modifications and upgrades as engine control technology improved. This engine was produced continuously for 42 years (even after Chrysler's buyout of AMC in 1987) all the way through 2006. It featured a durable design with a cast-iron block and cylinder head, hydraulic lifters (with non-adjustable rockers), and seven main bearings. Since AMC cars were designed to take the weight of an optional V8, AMC was able to make their straight-sixes much stronger and heavier than they needed to be. As a result, the engine blocks were so sturdy that some were used in race cars in the Indianapolis 500. In the 1978 race, an AMC 199 cu in (3.3 L) engine built by Navarro produced 875 hp (652 kW; 887 PS) at 8500 rpm with 80 in (2,000 mm) (24.6 lbs) of manifold pressure.
  Ford and General Motors straight-sixes of the 1960s and 1970s were generally no
caption: 1954 Hudson Wasp I6
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