Standard Hornet 308
1951–1956145 hp at launch; later approximately 160–165 hp
Base high-torque Hornet engine
Hudson 308 Hornet Six enginePhoto: Michael Barera · CC BY-SA 4.0
Hudson · Hornet 308
Hudson 308 Hornet Six
The big-bore, long-stroke flathead six that turned the low-slung Hornet into an early NASCAR powerhouse.
308
Cubic inches
The 308 combined massive displacement for a six with Hudson's low Step-Down chassis, producing a package that beat many contemporary V8s on both road and oval tracks.
Key variants
All variantsStandard Hornet 308Twin-H Power 3087X competition 308
Displacement
308 ci
Bore
3.8125"
Stroke
4.5"
Years
1951–1956 Hudson/Hornet family era
Key Takeaway
The 308 combined a 3.8125-inch bore with a 4.50-inch stroke in Hudson's robust wide-block flathead six. Huge displacement per cylinder, strong low-rpm torque, and the Step-Down chassis made the package exceptionally effective in early stock-car racing.
Technical Specifications
- Compression
- 7.2:1 in documented 1951–52 standard specification
- Horsepower
- 145 hp @ 3800 rpm at 1951 introduction; later standard versions reached roughly 160–165 hp
- Torque
- 257 lb-ft @ 1800 rpm in 1951–52 specification
- Architecture
- L-head inline six
- Block
- High-chromium-alloy cast iron in key Hornet descriptions
- Cylinder heads
- Cast iron; aluminum/high-compression variants existed
- Valvetrain
- Side-valve L-head, mechanical lifters
- Aspiration
- Naturally aspirated
- Fuel delivery
- Carbureted
- Firing order
- 1-5-3-6-2-4
- Main bearings
- 4
The 308 combined a 3.8125-inch bore with a 4.50-inch stroke in Hudson's robust wide-block flathead six. Huge displacement per cylinder, strong low-rpm torque, and the Step-Down chassis made the package exceptionally effective in early stock-car racing.
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
- 308 Hornet six — identify by Hornet engine serial/application plus 3.8125 x 4.50-inch bore/stroke; competition engines require additional 7X/Twin-H hardware verification
- Casting numbers
- No single casting number alone is treated as proof of a production or race-spec 308; verify block/head casting and date together with bore/stroke, serial, compression head and induction package.
- Power rating
- Period brake horsepower / SAE gross-era rating
- Horsepower RPM
- 145 hp @ 3800 rpm at 1951 introduction; later standard versions approximately 160–165 hp
- Torque RPM
- 257 lb-ft @ 1800 rpm in 1951–1952 standard specification
Operating Specs
- Production notes
- Introduced for 1951, the 308 enlarged Hudson’s wide-block six to 3.8125 x 4.50 inches. Twin-H induction and the 7X competition package progressively developed the same core engine for street and race use.
Compatibility Notes
- Standard, Twin-H and 7X engines share the 308 family but differ in head/compression, camshaft, valves, induction, exhaust and selected internal preparation; do not label a Twin-H engine as 7X without supporting hardware/history.
- Later 1955–1956 AMC-era Hudson installations can differ in chassis accessories and transmission interfaces from 1951–1954 Step-Down cars.
Notable Applications
Hudson HornetHudson police and competition applications
Strengths
- Huge displacement per cylinder
- Strong 257-plus-lb-ft torque
- Excellent period racing pedigree
- Robust block
Weaknesses / Watch-outs
- Four-main-bearing crank
- Flathead airflow ceiling
- Very long 4.5-inch stroke
Common Upgrades
- Twin-H dual carburetors
- Higher-compression head
- 7X-style cam/valve/port work
Racing History & Legacy
The 308-powered Hornet became one of NASCAR's defining early stock cars. Hudson-powered drivers won three consecutive NASCAR Grand National championships: Herb Thomas in 1951, Tim Flock in 1952, and Herb Thomas again in 1953.
The 308 transformed Hudson from an innovative independent automaker into an early NASCAR powerhouse. Its combination of large displacement, low-rpm torque and the Step-Down chassis became one of the defining stock-car formulas of the early 1950s.
References & Image Credit
Engine image: Michael Barera · CC BY-SA 4.0 · source
Classic Car Database — 1951 Hornet 308 specifications
period spec
NASCAR — Marshall Teague and Hudson history
racing history
NASCAR — all-time Cup Series champions
racing history
NASCAR — Herb Thomas Hall of Fame profile
racing history
Hudson Motor Car technical service bulletin — 1948–56 six-cylinder engine information
factory service bulletin
1954 Hudson technical data — six-cylinder firing order and ignition specifications
factory technical reference
Hudson Motor Car technical service bulletin — 1948–56 six-cylinder engine information
factory service bulletin
Hudson 7X engine technical reference
technical reference
Approved catalog media — Wikimedia Commons
licensed media
Key Factory / Build Variants
Twin-H Power 308
1951 dealer kit; 1952–1956 factory eraApproximately 160–175 hp depending year
Dual-carb signature performance version
7X competition 308
1952–1954 core competition eraApproximately 210–220 hp depending setup
Factory-developed racing specification
Engineering Notes Worth Knowing
01
308 cu in / 5.0 L with 3.8125 x 4.50-inch bore and stroke.
02
High-strength cast-iron L-head inline-six.
03
Factory launch output: 145 hp and 257 lb-ft; later standard versions increased output.
04
The basis for Twin-H and factory 7X competition development.
History · context · related reading
The Story Behind Hudson 308 Hornet Six
The 308 Hornet proved a flathead six could beat newer overhead-valve V8s when the whole package was right. Big torque, a low chassis, and relentless factory development turned Hudson into an early NASCAR powerhouse.
Documented motorsport results
Famous Race Wins
01
1951
Series championNASCAR Grand National championship
Driver
Herb Thomas
Car / engine
Hudson Hornet
Herb Thomas wins Hudson's first title
Herb Thomas won the 1951 NASCAR Grand National championship, with most of his season victories coming after switching to the factory-supported Hudson Hornet effort.
02
1952
Series championNASCAR Grand National championship
Driver
Tim Flock
Car / engine
Hudson Hornet
Tim Flock keeps Hudson on top
Tim Flock won the 1952 NASCAR Grand National championship driving Hudson power, extending the Hornet's championship streak.
03
1953
Series championNASCAR Grand National championship
Driver
Herb Thomas
Car / engine
Hudson Hornet
Herb Thomas wins a second title
Herb Thomas returned to the top of the standings in 1953, giving Hudson three consecutive NASCAR Grand National championships.
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