TorqueList Original Technical Art
GMC 270 Inline-Six
Inline6 · N/A
GMC · GMC Raised-Deck Inline-Six
GMC 270 Inline-Six
The long-lived raised-deck GMC six that became a favorite in trucks and early inline-six hot-rodding.
270
Cubic inches
The 270 moved GMC to the taller raised-deck six and became the bridge between conventional truck duty and the more performance-oriented 302.
Displacement
270 ci
Bore
3.78125"
Stroke
4"
Years
1941–1963
Key Takeaway
The 270 moved GMC into the taller raised-deck straight-six family and used a full 4.00-inch stroke with a 3.78125-inch bore. That long-stroke geometry favored torque and commercial durability, while the taller block created room for the larger 302 that followed.
Technical Specifications
- Horsepower
- 104 hp in 1949 listing; 130 hp in 1953; 133 hp in later 1963 specification
- Torque
- About 244 lb-ft in later specification
- Architecture
- OHV inline six, raised-deck GMC family
- Block
- Cast iron
- Cylinder heads
- Cast iron
- Valvetrain
- Pushrod OHV
- Aspiration
- Naturally aspirated
- Fuel delivery
- Carbureted
The 270 moved GMC into the taller raised-deck straight-six family and used a full 4.00-inch stroke with a 3.78125-inch bore. That long-stroke geometry favored torque and commercial durability, while the taller block created room for the larger 302 that followed.
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.
Notable Applications
Strengths
- Strong 4.00-inch stroke torque
- Heavy-duty construction
- Good vintage hot-rod reputation
Weaknesses / Watch-outs
- Large and heavy
- Lower breathing potential than 302
- Long-stroke design favors torque over rpm
Common Upgrades
- 302 cylinder-head/intake strategies where compatible
- Dual carburetors
- Headers and ignition upgrades
Racing History & Legacy
The 270 is remembered as the bridge between GMC’s early low-deck sixes and the legendary 302. It carried the raised-deck family into mainstream truck use and became a respected vintage hot-rod foundation in its own right.
References & Image Credit
Engineering Notes Worth Knowing
3.78125 x 4.00-inch bore and stroke; 270 cu in / 4.4 L.
Raised-deck GMC OHV inline-six architecture.
Period ratings ranged from roughly 104 hp in 1949 to about 133 hp in later specifications.
Used in GMC pickups, 400/450 series trucks, medium-duty trucks, and later van applications.
History · context · related reading
The Story Behind GMC 270 Inline-Six
The 270 was where GMC’s straight-six program grew into a more serious heavy-duty design. Its taller deck and four-inch stroke gave it the low-rpm character truck buyers needed, while also creating the architecture that performance-minded builders would later associate with the 302.
TorqueList Garage Reference Series
See this engine inside the full GMC reference catalog.
The same Engine Library data now powers a more detailed mobile-friendly catalog with technical specs, variants, engineering notes, history and related stories.