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400 Small-Block

Small-Block Chevrolet

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Most of us would rather forget the dismal '70s. Yet it was during this period that Chevy produced the biggest stock small-block ever built--the 400. Basically truck and heavy-sedan motors, no high-perf 400s were ever factory-produced. Nevertheless, in the hands of rabid car crafters, the engine has demonstrated its potential, whether destroked to 377 ci (0.030-inch overbore plus the 350 small-block's 3.48-inch stroke) or bored out to 407 ci (plus 0.030 inch with the existing 3.75-inch stroke).

A successful 400 buildup requires slightly different techniques than the ones normally used on its shorter-stroke sisters. The long 3.75-inch stroke combined with the 400's short 5.565-inch connecting rods yields a 1.48:1 rod/stroke ratio, which is not conducive for building a high-winding engine. The 400's rather severe rod angularity and high piston speed put high thrust loads on the cylinder walls. For these reasons, the savvy 400 builder would do well to concentrate on building for low and midrange torque. Premium head gaskets and precision machining and assembly techniques are recommended to avoid head-gasket problems on this siamesed cylinder-wall engine. CC

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