GMC V6 engine
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GMC produced a unique 60° V6 V6 engine from 1960 through 1978. The engine was available in 305, 351, 401 and 478 in³ (5.0, 5.8, 6.6, and 7.8 L) version. In late production there was also a 432 in³ (7.1 L) version with enlarged crankshaft journals. GM also made a 637 in³ (10.4 L) 60° V8 with twin balance shafts using the same general layout as the 305. Finally, there was a 702 in³ (11.5 L) "Twin Six" V12, which was basically two 351s placed end-to-end and was used in full-sized commercial trucks. A Diesel version was sold for marine applications as the ToroFlow.
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[edit] 305
The 305 in³ (5.0 L) 305 had a 4.25 in (107.9 mm) bore. The 305 V6 was the standard pickup truck engine for GMC from 1960 to 1966, and was one of the first V6 engines produced by an American company.
[edit] 351
The 351 in³ (5.8 L) 351 was an enlarged 305. In 1972, the 351 was replaced by a 379.
[edit] 401
The engine was further enlarged for the 401 in³ (6.6 L) 401. this engine was used in the 67 model
[edit] 432
In late production there was also a 432 in³ (7.1 L) version with enlarged crankshaft journals.
[edit] 478
The 477.7 in³ (7.8 L) 478 was one of the largest V6 engines ever built. Gross output was 235 hp (175 kW) at 3200 rpm and 440 ft.lbf (597 Nm) at 1400 rpm. Bore was 5.125 in (130.2 mm) and stroke was 3.86 in (98 mm). It was introduced in 1963 in the 6500 series trucks.
It was superseded by the 1966 478M "Magnum" series, and production ended by 1974. Gross output was now 254 hp (189 kW) at 3700 rpm and 442 ft.lbf (599 Nm) at 1400 rpm.
[edit] 702
The massive 702 in³ (11.5 L) V12 "Twin Six" was offered in United States GMC commercial trucks, and as a special order option in Canada. It was simply a pair of 351 in³ (5.8 L) V6 engines mated together. It used two separate exhaust manifolds, two separate distributors, and other parts from the 351. 56 major parts are interchangeable between the Twin-Six and the other GMC V-6 engines to provide greater parts availability and standardization. It produced 250 net SAE horsepower (190 kW). Torque was 585 lbf·ft (793 N·m).
