GMC V6 engine
The GMC V6 is a family of 60-degree V6 engines produced by the GMC division of General Motors from 1959 through 1974. It was developed into both gasoline and diesel versions, and produced in V8 and V12 derivatives. Examples of this engine family were found in pickup trucks, Suburbans, heavier trucks, and motor coaches.
| GMC V6 engine | |
|---|---|
GMC "Twin Six" heavy duty engine 702 cu in (11.5 L) | |
| Overview | |
| Manufacturer | General Motors |
| Production | 1959–1974 |
| Layout | |
| Configuration | 60° V6, V8, and V12 |
| Displacement |
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| Cylinder bore |
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| Piston stroke |
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| Cylinder block material | Cast iron |
| Cylinder head material | Cast iron |
| Valvetrain | OHV 2 valves × cyl. |
| Combustion | |
| Fuel system | Carburetor |
| Fuel type | Gasoline and diesel |
| Cooling system | Water-cooled |
| Output | |
| Power output | 150–275 hp (112–205 kW) |
| Torque output | 260–630 lb⋅ft (353–854 N⋅m) |
A big-block engine, variants were produced in 305-, 351-, 401-, and 478-cubic-inch (5.0, 5.8, 6.6, and 7.8 liters respectively) displacements, with considerable parts commonality. During the latter years of production, 379-and-432-cubic-inch (6.2 and 7.1 L) versions with enlarged crankshaft journals were manufactured as well.
GMC produced a 637-cubic-inch (10.4 L) 60° V8 with a single camshaft using the same general layout (bore and stroke) as the 478 V6. The 637 V8 was the largest-displacement production gasoline V8 ever made for highway trucks.
The largest engine derived from the series was a 702-cubic-inch (11.5 L) "Twin Six" V12, which had a unique block and crankshaft, but shared many exterior parts with the 351.
Diesel versions of the 351, 478 and 637, advertised as the ToroFlow, were also manufactured. These engines had no relationship to the well-known Detroit Diesel two-stroke diesel engines produced by General Motors during the same time period.
All versions of the GMC V6 used a six-throw crankshaft, which when combined with the 60 degree included cylinder angle, produced a smooth-running engine without any need for a balance shaft. Spark plugs were located on the inboard side of the cylinder heads and were accessed from the top of the engine. This position allowed for shorter spark-plug wires and kept the spark plugs away from the hot exhaust manifolds, something which was emphasized in sales literature. It was also perceived as being easier to access for maintenance. These GMC V6 engines were noted for durability, ease of maintenance, and strong low-end torque.
In 1974, GMC discontinued the V6 engine; all gasoline-engine models were powered by Chevrolet straight-six and V8 engines, while diesel engines were dropped from medium duty models and would not return until 1976.