GMC V6 engine

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GMC Truck produced a unique 60° V6 engine from 1960 through 1974. The engine was available in 305, 351, 401, and 478-cubic-inch (5.0, 5.8, 6.6, and 7.8 respectively L) versions. In late production there was also a 432-cubic-inch (7.1 L) version with enlarged crankshaft journals. GMC also made a 637-cubic-inch (10.4 L) 60° V8 with single, not twin balance shafts using the same general layout(bore & stroke) as the 478. The 637 V8 was the largest production gas V8 ever made for highway trucks. Finally, there was a 702-cubic-inch (11.5 L) "Twin Six" V12, which was basically two 351s placed end-to-end with a common block and crank. A Diesel version of the 351, 478 and the 637 were called the ToroFlow.


The 304.6-cubic-inch (5.0 L) 305 had a 4.25 in (108 mm) bore and 3.578 in stroke (90.9 mm). The 305 V6 was the standard pickup truck and Suburban engine for GMC from 1960 to 1969, and was one of the first V6 engines produced by an American company. It was rated at 280 of torque and 152 horsepower.


The 351-cubic-inch (5.8 L) 351 had a 4.562 in (115.9 mm) bore and 3.578 in stroke (90.9 mm). It was basically an enlarged 305. In 1973, the 351 was replaced by a 379.


The 378.6-cubic-inch (6.2 L) 379 had a 4.562 in (115.9 mm) bore and 3.859 in stroke (98 mm).


[1] The engine was further enlarged for the 400.7-cubic-inch (6.6 L) 401.It has a 4.875 in (123.8 mm) bore and 3.578 in stroke (90.9 mm). Produced from 1960 through 1972.


In 1973 & 1974 there was also a 432.2-cubic-inch (7.1 L) version with enlarged crankshaft journals (bore 4.875", stroke 3.859").


The 477.7-cubic-inch (7,828 cc) 478 was one of the largest V6 engines ever built. Gross output was 235 hp (175 kW) at 3200 rpm and 440 lb·ft (597 Nm) at 1400 rpm. Bore was 5.125 in (130.2 mm) and stroke was 3.859 in (98.0 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It was superseded by the 1966 478M "Magnum" series, and production ended by 1974.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 lb·ft (599 Nm) at 1400 rpm.


The 702-cubic-inch (11.5 L) V12 "Twin Six" was offered in United States GMC commercial trucks, and as a special order option in Canada. It was mistaken as two V6 engines welded together, but it is its own separate engine design based on a single casting.[2] It used four separate exhaust manifolds, two separate carburetors, two separate distributor caps driven by a single distributor drive,[2] 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 lb·ft (793 N·m).

See also[edit]


  1. ^ gmc truck parts & illustration manual 1955-1964,1965-7
  2. ^ a b "GMC Twin-Six V12 Myths". 6066 GMC Trucks. June 1, 2007. Retrieved 2008-10-05.