Miller 122

Engine architecture

When the AAA restricted top-tier engine limits from 183 cubic inches down to 122 cubic inches for the 1923 season, Miller scaled down his successful 183 straight-eight engine design. The resulting powerplant displaced 121.3 cubic inches (1,988 cc).

• Block & Head: The cast-iron cylinder heads were cast integrally with the cylinder blocks (divided into two distinct four-cylinder blocks) sitting atop a barrel-type aluminum crankcase.
• Valvetrain: Double overhead camshafts (DOHC) activating two valves per cylinder within hemispherical combustion chambers.
• Craftsmanship: True to Miller's signature ethos, parts were treated as automotive jewelry. Castings were meticulously hand-scraped to a polished sheen, and components underwent rich gun-bluing.

Supercharging and evolution

When originally introduced in 1923, the naturally aspirated engine generated roughly 150 brake horsepower (bhp) at 5,000 rpm. However, following the introduction of forced induction by rival Duesenberg in 1924, Miller rapidly engineered a massive, gear-driven centrifugal supercharger for the 1925 season. Pushing high-volume boost, the supercharged Miller 122 variant experienced a dramatic power surge, generating 235 bhp at 5,800 rpm.

Chassis and body layout

The vehicle was intentionally packaged to minimize frontal area and aerodynamic drag. The steel ladder-frame chassis carried a bodywork skin that measured an incredibly narrow 18 inches wide at the cockpit. Drivers had to be physically slight to fit, and the three-speed manual gear shifter sat directly between their legs. The total dry weight of the vehicle was remarkably light, scaling at just 1,350 pounds (612 kg). In late 1924, Miller broke new engineering ground by introducing a revolutionary front-wheel-drive (FWD) configuration for the 122 chassis. Utilizing a rigid De Dion tube front axle assembly paired with quarter-elliptic leaf springs, the FWD architecture eliminated the central driveshaft. This allowed the cockpit floor to drop significantly, lowering the center of gravity and providing superior pulling power out of banked turns.

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  1924 Miller 122-91
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  1923 Miller 122 HCS Special No. 1
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  1923 Miller 122
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• 
  1925 Miller 122-2
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  1923 Miller 121.3 cu in DOHC Straight 8 engine
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  1922 Miller 122-91 Engine

1923 Indianapolis 500 debut

The Miller 122 made a dominant debut at the 1923 Indianapolis 500. Wealthy sportsman Cliff Durant, son of General Motors founder William Crapo Durant, purchased five of the first seven completed factory vehicles. In total, seven Miller 122 entries were arrayed on the grid. Tommy Milton drove his H.C.S. Motor Co. Special Miller 122 to pole position with a qualifying speed of 108.17 mph, later winning the race with a three-lap lead. Five of the top ten finishers that year piloted Miller 122 chassis.

Supremacy and global records

Through the 1924 and 1925 seasons, the car became the absolute default choice for professional racing teams. In naturally aspirated form, the car reached top speeds of 141.17 mph (227.14 km/h). With the introduction of the supercharged FWD variants, lap speeds skyrocketed on the hazardous board tracks of the era.

Year	Event / Venue	Driver	Layout / Entry Name	Race Result / Historic Milestone
1923	Indianapolis 500	Tommy Milton	Rear-Wheel Drive; H.C.S. Special	Race Winner & Pole Position; Milton became the first two-time Indy 500 winner.
1923	Italian Grand Prix (Monza)	Jimmy Murphy	Rear-Wheel Drive; Count Zborowski Entry	3rd Place; Historic early podium finish for an American car in European Grand Prix racing.
1924	Indianapolis 500	Jimmy Murphy	Rear-Wheel Drive; Miller Special	3rd Place; One of eight Miller vehicles to occupy the top ten finishing slots.
1925	Indianapolis 500	Dave Lewis	Front-Wheel Drive; Junior 8 Special	2nd Place; The competitive debut of Miller's pioneering front-wheel-drive concept.
1925	Culver City Board Track	Bennett Hill	Supercharged Rear-Wheel Drive	Race Winner; Averaged a blistering 126.9 mph over a 250-mile duration.

Technical specifications (1925 Supercharged Variant)

Bibliography

• Borgeson, Griffith (1993). Miller. Motorbooks International. ISBN 978-0-8793-8714-3.
• Dees, Mark (1994). The Miller Dynasty. The Barnes Foundation. ISBN 978-0-9642-6420-5.