The Ford 406 was a member of the Ford 'FE' series of engines. People sometimes say that the 'FE' is used for cast-iron (the chemical symbol for iron is FE). It actually stands for Ford Edsel, a designation used by Ford to distinguish the engine family.
The Ford FE engine is a Ford V8 engine used in vehicles sold in the North American market between 1958 and 1976. The FE was introduced to replace the short-lived Ford Y-block engine, which American cars and trucks were outgrowing. It was designed with room to be significantly expanded, and manufactured both as a top-oiler and side-oiler, and in displacements between 330 cubic inches and 428 cubic inches.
"FE" derives from 'Ford-Edsel'. Versions of the FE line designed for use in medium and heavy trucks and school buses from 1964 through 1978 were known as "FT," for 'Ford-Truck,' and differed primarily by having steel (instead of nodular iron) crankshafts, larger crank snouts, different distributor shafts, different water pumps and a greater use of iron for its parts.
Because the FE was never a completely static design and was constantly being improved by Ford, references to a particular version of the FE can become difficult. Generally though, most FEs can be described using the following descriptors:
1) Carburetor count, i.e. single 2V (two-barrel), single 4V, dual quad (two 4V carburetors), tripower (three 2V carburetors) or weber (four 2V weber carburetors).
2) Top-oiler or side-oiler block (though there are known instances of side-oiler blocks drilled at the factory as top-oilers; perhaps to salvage blocks with quality control issues that prevented them from being completed as side-oilers).
3) Head type: low-riser, medium-riser, high-riser, tunnelport, or SOHC. These descriptions actually refer to the intakes used with the heads...a low-riser intake, designed to fit under a low hoodline was the earliest design. The high-riser intake required a bubble in the hood of cars it was installed in for clearance. While the low and medium riser heads could be used in combination with either low or medium riser intakes, the high riser head required a high-riser intake due to the increased height of the intake port. The medium riser's intake port is actually shorter in height, though wider, than the low-riser's port. The high-riser's ports are taller than either the low or medium-riser ports. Low-riser intakes have the carburetor placed relatively low so that the air-fuel mix must follow a more convoluted path to the chamber. A high-riser's intake places the carburetor approximately 6 inches higher so the air-fuel mixture has a straighter path to the chamber. The tunnelport and SOHC heads both bolted onto FE blocks of either variety but required their own matching intakes. Within the major head groups, there were also differences in chamber designs, with small chambers, machined chambers and large chambers. The size and type of chamber affected the compression ratio, as well as the overall performance characteristics of the engine.
The 406 engine used a new 4.13-inch bore with the 390's 3.785-inch stroke, giving a displacement of 405.7 cubic inch, rounded up to "406" for the official designation. The larger bore required a new block casting design allowing for thicker walls, but otherwise was very similar to the 390 block.
It was available for less than two years before it was replaced by the 427.
Testing of the 406, with its higher power levels, led to cross-bolted mains – that is, main bearing caps that were secured not only by bolts at each end coming up from beneath, but also by bolts coming in from the sides through the block. A custom fit spacer was used between the cap and the block face. This design prevented the main bearing caps from "walking" under extreme racing conditions, and can be found today in many of the most powerful and modern engines from many manufacturers.
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