Packard 473 Twelve enginePhoto: brewbooks · CC BY-SA 2.0

Packard · Packard Twelve

Packard 473 Twelve

The late-production Packard Twelve, combining enormous luxury-car torque with twelve-cylinder smoothness.

473

Cubic inches

Packard's Twelve represented the company's prewar prestige peak. The 473-cubic-inch late version powered some of the most expensive American production and coachbuilt cars of the era.

Key variants

All variantsStandard 473 Packard TwelveHigh-compression Twelve

Displacement

473 ci

Bore

3.4375"

Stroke

4.25"

Years

1935–1939 473-cubic-inch Packard Twelve era

Key Takeaway

Packard’s 473 Twelve used a 67-degree side-valve V12 layout with a 3.4375-inch bore and 4.25-inch stroke. Its nearly 7.8-liter displacement, low compression, and many-cylinder architecture prioritized silent operation, smooth torque, and effortless movement of large coachbuilt luxury cars.

Technical Specifications

Compression: 6.4:1 in documented 1938 standard specification; high-compression versions varied
Horsepower: 175 hp in documented late Packard Twelve specifications
Torque: Approximately 322 lb-ft in standard 175-hp period specification; Packard Proving Grounds notes later/high-compression Twelve development reaching as much as 366 lb-ft
Architecture: 67-degree side-valve V12
Block: Cast iron
Cylinder heads: Cast iron/aluminum depending period specification
Valvetrain: Side-valve L-head
Aspiration: Naturally aspirated
Fuel delivery: Carbureted
Firing order: Packard period bank notation: 1R-6L-4R-3L-2R-5L-6R-1L-3R-4L-5R-2L

Internal Specifications

Variant-specific values are labeled. Engine families that span multiple years or RPOs can have different heads, cams, induction and rotating parts, so the exact code/year always takes priority.

Identification & Output

Engine codes / RPO: Packard Twelve motor-number ranges are series-specific; representative 1938 16th-Series 473 motor range A600001–A600621
Casting numbers: No single universal casting number is retained for the 1935–1939 Twelve; identify by Packard motor number, 67-degree V12 architecture, 3.4375 x 4.25-inch bore/stroke and series.
Power rating: Period brake horsepower / SAE gross-era rating
Horsepower RPM: 175 hp @ 3200 rpm standard documented rating; Packard literature described more than 175 hp and high-compression versions could reach approximately 180 hp
Torque RPM: Approximately 322 lb-ft in standard period specification; peak commonly cited near 1400 rpm, while high-compression late development could reach higher torque

Operating Specs

Production notes: Packard enlarged its V12 from 445.5 to roughly 473.3 cid for the 12th Series beginning in the 1935 model year. The 67-degree side-valve V12 continued through 1939 and represented the peak of Packard’s prewar multi-cylinder luxury engineering.

Compatibility Notes

The 473 Twelve is a specialized senior Packard engine with model-specific ignition, carburetion, cooling and chassis interfaces; parts should be matched by motor/series number rather than generic Packard V12 description.
High-compression heads and late-production changes can alter compression/output, so restoration specifications should be tied to the exact series and engine number.

Notable Applications

Packard Twelve sedanPackard Twelve limousinePackard Twelve convertibleCoachbuilt Packard Twelve models

Strengths

Exceptional smoothness
Huge low-speed torque
Prestige engineering and coachbuilt history

Weaknesses / Watch-outs

Extremely expensive to rebuild
Large and heavy
Specialist parts and machining required

Common Upgrades

Strict preservation-focused restoration
Modern internal materials where invisible
Cooling and ignition reliability improvements

Racing History & Legacy

The Packard Twelve was engineered for refinement, silent operation and effortless heavy-car performance rather than sanctioned racing. Packard tested these cars extensively at its Proving Grounds, but the V12’s reputation came from luxury-car smoothness and torque rather than a works competition program.

The 473 Twelve was Packard's ultimate prewar multi-cylinder luxury engine.

References & Image Credit

Engine image: brewbooks · CC BY-SA 2.0 · source

Packard Club Twelve reference data

club reference

Packard engine bore/stroke reference

dimension reference

1937 Packard factory brochure — Twelve engine specification

manufacturer brochure

Period automotive reference — Packard Twelve firing order

period technical reference

Packard Proving Grounds — Packard V12 engineering history

museum history

Packard Club — year/model/motor-number identification reference

club identification reference

Key Factory / Build Variants

Standard 473 Packard Twelve

1935–1939

175 hp @ 3200 rpm

Final large-displacement Packard V12

High-compression Twelve

late production / special specification

Up to about 180 hp and higher torque

Optional/special higher-output version

Engineering Notes Worth Knowing

3.4375 x 4.25-inch bore and stroke; 473 cu in / 7.8 L.

67-degree L-head V12 with cast-iron block.

Late Packard Twelve output: about 175 hp.

Representative torque was roughly 322 lb-ft, with higher figures documented in later/high-compression development.

History · context · related reading

The Story Behind Packard 473 Twelve

At the top of prewar Packard sat the Twelve, an engine built less for speed than for absolute refinement. The 473-cubic-inch version powered some of America’s most prestigious sedans, limousines, convertibles, and coachbuilt cars.

TorqueList Garage Reference Series

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