TorqueList Technical Reference
Rambler Flathead Six
Nash 172.6 L-Head Six
The compact flathead six developed for Nash's early unit-body cars and the first Rambler.
172.6
Cubic inches
TorqueList Original Technical Art
Nash 172.6 L-Head Six
Inline6 · N/A
Why it matters
Key takeaway
The 172.6 was designed for Nash's lighter unit-body cars and became the starting point for the 184 and 195.6 six-cylinder family.
Key variants
Engineering
Technical specification
- Architecture
- L-head inline six
- Block
- Cast iron
- Cylinder heads
- Cast iron
- Valvetrain
- Side-valve L-head
- Aspiration
- Naturally aspirated
- Fuel delivery
- Carbureted
- Firing order
- 1-5-3-6-2-4
- Main bearings
- 4
The 172.6 used a 3.125-inch bore and 3.75-inch stroke in a compact cast-iron flathead six. Nash designed it for lighter unit-body cars, where modest size, simplicity, and fuel economy mattered more than outright output.
Builder reference
Internal Specifications
Variant-specific values are labeled. For engine families with multiple factory combinations, the exact RPO/code/year takes priority over the family summary.
Identification & Output
- Engine codes / RPO
- Nash/Rambler 172.6 L-head six — pre-AMC identification is primarily by engine serial/stamp and vehicle application rather than a single RPO-style code
- Casting numbers
- The reviewed Nash/Rambler sources do not establish one universal 172.6 block/head casting for the full 1941–1952 run; verify the block/head casting together with engine serial, stroke and model-year application.
- Power rating
- Period brake horsepower / SAE gross-era rating
- Horsepower RPM
- 82 hp @ 3800 rpm in documented 1951–1952 Rambler specification
- Torque RPM
- 138 lb-ft @ 1600 rpm in documented 1951 specification
Operating Specs
- Production notes
- Designed for Nash’s first major unibody-era cars, the 172.6 used a 3.125-inch bore and 3.75-inch stroke. Nash retained the bore while increasing stroke for the later 184 and 195.6 versions.
Compatibility Notes
- The 172.6, 184 and 195.6 L-head engines share family architecture, but compression-chamber volume, crank/stroke, water-pump location and year-specific external hardware vary.
- Do not interchange an OHV 195.6 cylinder head or valvetrain onto an L-head block as if it were a simple top-end swap; the OHV redesign includes major oiling/cooling and component differences.
Factory fitment
Notable applications
Versions that matter
Key factory / build variants
172.6 Nash 600 / early unibody six
Original short-stroke member of Nash’s compact L-head six family
1941–1949 core era
Application/year dependent
172.6 Nash Rambler
Compact-car version before the Rambler moved to 184/195.6 displacements
1950–1952
82 hp @ 3800 rpm representative
Strengths
- Simple durable construction
- Compact packaging
- Important Nash unit-body history
Watch-outs
- Flathead airflow limits power
- Long-stroke economy-oriented design
- Limited modern aftermarket
Common upgrades
- Electronic ignition
- Carburetor rebuild
- Cooling-system restoration
Builder notes
Engineering notes worth knowing
172.6 cu in / 2.8 L with 3.125 x 3.75-inch bore and stroke.
Cast-iron L-head inline-six.
Carbureted and naturally aspirated.
Documented 1951 output: 82 hp and 138 lb-ft.
History & context
The story behind the engine
The 172.6 was the small engine behind Nash's lightweight unit-body strategy. It prioritized efficiency and packaging and became the foundation for a six-cylinder family that would survive well into the AMC era.
Racing history
The 172.6 was developed as a compact, economical production engine rather than a factory competition unit. Its significance is the lightweight Nash unibody/Rambler platform it helped establish; Nash’s major international racing successes came later with the larger OHV Ambassador sixes in the Nash-Healey.
Legacy
The 172.6 was the foundation of Nash’s long-lived small inline-six family. The same 3.125-inch bore architecture was stroked to 184 and then 195.6 cubic inches, ultimately surviving into the AMC era.
Verification
Reference sources
AMC Magazine — Rambler 195.6 engine history
technical history
1951 Nash brochure — 172.6 Rambler engine specifications
manufacturer brochure
Automotive ignition reference — standard inline-six firing order
technical reference
AMC Magazine — Nash/Rambler 172.6, 184 and 195.6 engine-family history
technical history
TorqueList independent reference · Not an OEM publication or endorsement. Original TorqueList editorial and layout rights reserved.
