GMC V6 engine

GMC Truck produced a unique 60 degree V6 engine family from 1959 through 1974, in gasoline and Diesel versions. V8 and V12 derivatives of the basic design were also produced. Examples of this engine family were found in pickup trucks, Suburbans, heavier trucks and motor coaches.

V6 engines were produced in 305, 351, 401 and 478 cubic-inch (5.0, 5.8, 6.6, and 7.8 respectively liter) displacements, with considerable parts commonality. During the latter years of production, a 432-cubic-inch (7.1 L) version with enlarged crankshaft journals was manufactured as well.

GMC produced a 637-cubic-inch (10.4 L) 60° V8 with a single balance shaft 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 was basically two 351 V6s placed end-to-end with a common block and crankshaft.

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 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 reduced the likelihood of water being splashed on to the spark plugs and causing the engine to misfire or stall. GMC V6 engines were noted for durability, ease of maintenance and strong low RPM torque.

The 304.6-cubic-inch (5.0 L) 305 had a 4.25 in (108 mm) bore and 3.58 in stroke (90.9 mm). The 305 V6 was GMC's standard pickup truck and Suburban engine from 1960 to 1974, and was one of the first V6 engines produced by an American company. The 305A was equipped with a single barrel carburetor and produced 150 gross horse power at 3600 rpm and 260 gross torque at 1600 rpm. GMC also made a B,C,D and E version of the 305 v6. The E version producing 165 gross HP at 3600 rpm and 280 gross torque at 1600 rpm.

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