HISTORY: 400 / 6.6

[] 400 / 6.6L

4.125 in Bore

3.75 in Stroke

400 CID 1970-1981

  The 400 cu in (6.6 L) is the only engine in this family and was introduced in 1970 and produced for 10 years. It has a 4.125-inch bore and a 3.75-inch stroke. The 400 differed from other small blocks in that the cylinders were siamesed and therefore required 'steam' holes in the block, head gaskets, and heads to help alleviate 'hot-spots' in the cooling system at the point above the siamesed cylinders. Overheating and damage are likely if head gaskets or heads without 'steam' holes are used on a 400 block. The 400 is the only engine that uses a 2.65" main bearing journal and a 2.10" rod bearing journal. The connecting rod was also 400 specific being 5.565" as opposed to the 5.7" rod used in all other small block Chevrolet engines. The 400 was made in 4-bolt main journal from 1970 to 1972 and in 2-bolt main journal from 1973 to 1980. The 400 can have either 2 or 3 freeze-plugs per side though all 400 blocks have the provisions for a 3rd freeze-plug on each side. The 400 was rated at 245/265 horsepower (gross[150/180 HP net]) through its life. The 400 saw extensive use in full-size Chevrolet and GMC trucks; K5 Blazer/Jimmy, 1/2-ton, 3/4-ton, 1-ton, and even larger 'medium duty' trucks had an option to be equipped with a 400. The engine was available in midsize A-Body and full-size B-Body passenger cars until the end of the 1976 model year. Early models produced 265 horsepower with a two-barrel carburetor. All 400s came with a two-barrel carburetor with a four-barrel carburetor option becoming available in 1974. The 400 was never intended as a high-performance engine and never saw large factory horsepower numbers;however, it did develop a reputation for creating a tremendous amount of torque and has since become popular for many types of racing, both on and off road.

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