TorqueList Original Technical Art
GMC 248 Inline-Six
Inline6 · N/A
GMC · GMC Low-Deck Inline-Six
GMC 248 Inline-Six
The larger low-deck GMC six used in heavier light- and medium-duty trucks before the 270 took over.
248
Cubic inches
The 248 enlarged the 228's low-deck layout and became a common medium-duty GMC six through the first half of the 1950s.
Displacement
248 ci
Bore
3.71875"
Stroke
3.8125"
Years
1939–1955
Key Takeaway
The 248 enlarged the low-deck GMC straight-six while keeping the same 3.8125-inch stroke used by the 228. A larger 3.71875-inch bore raised displacement and torque without changing the basic cast-iron, pushrod-OHV, carbureted truck architecture.
Technical Specifications
- Horsepower
- 100 hp in 1949 GMC listing; 114 hp in 1953 listing
- Torque
- About 202 lb-ft in later commonly cited specification
- Architecture
- OHV inline six, low-deck GMC family
- Block
- Cast iron
- Cylinder heads
- Cast iron
- Valvetrain
- Pushrod OHV
- Aspiration
- Naturally aspirated
- Fuel delivery
- Carbureted
The 248 enlarged the low-deck GMC straight-six while keeping the same 3.8125-inch stroke used by the 228. A larger 3.71875-inch bore raised displacement and torque without changing the basic cast-iron, pushrod-OHV, carbureted truck architecture.
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
- More displacement than 228
- Durable truck-focused design
- Good low-speed torque
Weaknesses / Watch-outs
- Four-main-bearing architecture
- Low-deck family limits later parts interchange
- Modest top-end breathing
Common Upgrades
- Electronic ignition
- Carburetor tuning
- Period dual-carb or exhaust upgrades
Racing History & Legacy
The 248 represents the mature form of GMC’s low-deck six before the raised-deck 270 and 302 took over the higher-capacity role. It remains an important link in the company’s transition from prewar truck engines to the heavier postwar GMC sixes.
References & Image Credit
Engineering Notes Worth Knowing
3.71875 x 3.8125-inch bore and stroke; 248 cu in / 4.1 L.
Low-deck GMC OHV inline-six with cast-iron block and cylinder head.
Factory listings moved from about 100 hp in 1949 to 114 hp by 1953.
Commonly found in GMC 300–400 series and other medium-duty truck applications.
History · context · related reading
The Story Behind GMC 248 Inline-Six
The 248 was GMC’s straightforward answer to customers who needed more from the basic low-deck six without moving to a completely different engine family. It kept the familiar architecture of the 228 but added displacement and useful truck torque for heavier work.
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