Just the facts, maam. Typical flywheels, from left: A 15-pound, 12-3/4-inch-od nodular iron for a two-piece crank seal (PN 14085720); an externally balanced, 16-pound, 12-3/4-inch-od nodular iron for a one-piece crank seal (PN 14088646); an externally balanced, 14-inch-od 400 small-block flywheel (PN 3986394). Typical flywheels, from left: A 15-pound, 12-3/4-inch-od nodular iron for a two-piece cran Three freeze plugs per side identifies the rear block as a 400. But there are 400 blocks with only two plugs per side, similar to "regular" small-blocks. Some (but not all) two-plug 400s still retain an unmachined third plug hole (front block). All 400s bulge out slightly around cylinder No. 1. Three freeze plugs per side identifies the rear block as a 400. But there are 400 blocks w To aid water circulation at low engine speeds and vent steam pockets on the siamesed cylinder-wall 400 block, stock 400 heads have six steam holes (arrows) that align with corresponding holes in the block deck surface. Add these holes to non-400 heads and head gaskets unless the engine will operate primarily above 3,500 rpm. To aid water circulation at low engine speeds and vent steam pockets on the siamesed cylin 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 Enjoyed this Post? Subscribe to our RSS Feed, or use your favorite social media to recommend us to friends and colleagues!