Stutz straight-8 engine

The Stutz straight-8 engine, also known as the Stutz Vertical Eight engine or Stutz inline-eight, was a family of inline-eight automobile engines produced by the Stutz Motor Car Company of Indianapolis, Indiana, from 1926 to 1935. Designed by chief engineer Charles "Pop" Greuter, the engine was notable for its overhead-camshaft architecture and advanced valvetrain in an era when most American luxury and performance cars relied on simpler side-valve (flathead) designs. It powered the entire Stutz Vertical Eight series (including models such as the AA, BB, M, SV-16, and DV-32), helping reposition the company as a maker of high-performance luxury vehicles with exceptional smoothness, power, and handling characteristics. The engine family culminated in the sophisticated DV-32 variant, which featured double overhead camshafts and four valves per cylinder, delivering strong specific output and top speeds exceeding 100 mph (161 km/h) in production cars. Production of Stutz automobiles, and thus the engine, ended in 1935 amid the Great Depression.

Following Harry C. Stutz's departure from the company in 1919, new leadership under Frederick E. Moskovics sought to modernize the marque with a focus on safety and performance. The Vertical Eight, introduced for the 1926 model year as the "Safety Stutz," marked Stutz's first inline-eight-powered production car. Greuter's engine was engineered for smoothness and high-revving capability, paired with the innovative underslung "Safety Stutz" chassis that featured a low center of gravity, hydraulic four-wheel brakes, and safety glass.^[1] The engine quickly gained acclaim. Early Vertical Eight models set endurance records, and lighter sporting variants (such as the Black Hawk Speedster) were among the fastest American production cars of the late 1920s. Incremental refinements continued through the late 1920s and early 1930s, including bore increases, higher compression, and optional supercharging for competition use. The flagship DV-32 debuted in 1931 as Stutz's response to the multi-cylinder "cylinder race" among luxury marques, though the company remained committed to its high-revving inline-eight philosophy rather than switching to V-12 or V-16 designs. Stutz's financial difficulties during the Great Depression curtailed production; fewer than 300 DV-32 cars were built. Automobile manufacturing ceased by 1935, with the company shifting focus to commercial vehicles before its eventual dissolution.

The core Stutz inline-8 was a water-cooled, naturally aspirated (or optionally supercharged) straight-eight with a cast-iron block and aluminum components where appropriate for weight savings. Early versions featured a single overhead camshaft (SOHC) driven by an unusual link-belt chain, two valves per cylinder (16 total), dual ignition (twin spark plugs per cylinder in many examples), and a nine-main-bearing crankshaft for exceptional smoothness and durability. Fuel delivery typically used dual Zenith or Stromberg carburetors. Key design elements included a long stroke for strong low-end torque and an overhead-cam layout that allowed better breathing and higher rpm capability than contemporary flathead engines. The engine was mounted longitudinally at the front and drove the rear wheels via a three- or four-speed manual transmission (some with a "Noback" hill-holder device). Central lubrication and advanced oil filtration (such as the Wall Oil Rectifier) were standard.^[2]

• Early SOHC engines (1926–1928 AA/BB series): Initial displacement of 287 cu in (4.7 L) with bore × stroke of 3.19 in × 4.5 in (81 mm × 114 mm), producing 92 hp (69 kW) at 3,200 rpm. By 1927–1928, bore was increased to 3.25 in (83 mm), raising displacement to approximately 298–299 cu in (4.9 L) and output to 95–115 hp (71–86 kW). These featured dual ignition and delivered strong performance in lightweight bodies.
• SV-16 (1930–1935): Enlarged to 322 cu in (5.28 L) SOHC 16-valve configuration, rated at 115–130+ hp (86–97 kW). This served as the base powerplant for later Vertical Eight models.
• DV-32 (1931–1935): The most advanced variant, with double overhead camshafts (DOHC), four valves per cylinder (32 total), and hemispherical combustion chambers. Displacement remained 322.1 cu in (5.278 L) with bore × stroke of 3.375 in × 4.50 in (85.7 mm × 114.3 mm). Output was 156–161 hp (116–120 kW) at 3,900 rpm and approximately 300 lb⋅ft (407 N⋅m) of torque at 2,400 rpm. Specific output reached nearly 30 bhp per liter, exceptional for the era.^[3]
• Supercharged variants: Offered on certain 1929 Model M and competition cars, a front-mounted centrifugal supercharger ( Roots-type in some racing applications) boosted the 322 cu in engine to as much as 185 hp (138 kW). These were used in factory Le Mans entries.^[4]

Early SOHC (c. 1926–1927)

• Displacement: 287–298.6 cu in (4.7–4.9 L)
• Bore × stroke: 3.19–3.25 in × 4.5 in (81–83 mm × 114 mm)
• Power: 92–95 hp (69–71 kW) @ 3,200 rpm
• Valvetrain: SOHC, 2 valves/cylinder

DV-32 DOHC (1931–1935)

• Displacement: 322.1 cu in (5.278 L)
• Bore × stroke: 3.375 in × 4.50 in (85.7 mm × 114.3 mm)
• Power: 156 bhp (116 kW) @ 3,900 rpm
• Torque: 300 lb⋅ft (407 N⋅m) @ 2,400 rpm
• Valvetrain: DOHC, 4 valves/cylinder, hemispherical chambers

ApplicationsThe engine was used exclusively in Stutz automobiles, primarily the Vertical Eight series. Body styles ranged from factory Weymann fabric sedans and coupes to custom coachwork by LeBaron, Rollston, Brewster, and others. Sporting models included the Black Hawk Speedster and later revived Bearcat/Super Bearcat, which carried the DV-32 engine on a shorter 116-inch (2,946 mm) wheelbase.