Raising Compression on 460 Ford Enginesby John Stevens J.D.
Compression refers to the relationship between the volume of the cylinder and the cylinder heads with the piston at its highest point in the engine and the volume when the piston is at its lowest point. Compression partially determines how much power an engine produces. Increasing the compression will increase the power output. Ford used the 460 mostly for its truck line, where torque was emphasized over horsepower, so the 460 used a relatively low compression ratio. This makes the 460 ideal for a compression increase. Fortunately, there are several different ways to increase the compression in this engine.
Installing Dome-Top Pistons
The 460's stock pistons are either flat on top or slightly concave, meaning the top of the piston curves inward like a bowl. Dome-top pistons have convex tops, meaning that the surface of the piston actually curves outward rather than inward. Because the volume of the combustion chamber is reduced due to the convex top, the compression ratio will be higher than with the stock pistons. However, the disadvantage to installing dome top pistons is that it requires almost a complete disassembly of the engine.
Milling the Heads
Milling the cylinder heads is the most common way to increase compression. The cylinder heads are first removed from the engine, then taken to a machine shop. The heads are bolted to a milling machine, which gradually shaves down the portion of each head that bolts onto the engine. Because the volume of the combustion chambers is reduced by milling the heads, the compression ratio is increased. Having the heads milled is a relatively inexpensive option, but does carry the danger of too much metal being removed from the heads. Once the metal is removed, it cannot later be added.
Installing Different Cylinder Heads
Replacing the stock cylinder heads with heads that have smaller combustion chambers is a relatively easy way to raise the compression ratio. There are two possible ways to find cylinder heads with smaller combustion chambers than the stock cylinder heads: by locating cylinder heads manufactured by Ford with smaller combustion chambers, or by purchasing cylinder heads on the aftermarket. The first step with either option is to note the current compression ratio, which can be found in the engine's specifications manual, to ensure that the replacement heads have smaller combustion chambers that the existing heads. The next step is to determine whether Ford manufactured cylinder heads with smaller combustion chambers that will fit the 460. Cylinder heads from the 370- and 429-cubic-inch engines will bolt directly onto the 460. Use that engine's specification's guide to determine if it was ever produced with smaller combustion chambers. Purchasing new cylinder heads on the aftermarket is the easier way to find a pair of heads that will fit the 460 and increase its compression ratio. However, aftermarket heads can be expensive.
Installing Thinner Head Gaskets
Perhaps the cheapest and easiest way to increase compression is to replace the stock head gaskets with thinner gaskets, which will increase the compression ratio by reducing the volume of the combustion chambers. Several aftermarket companies produce thinner head gaskets, as thinner gaskets are commonly used for racing applications. However, installing thinner head gaskets will not raise the compression ratio as dramatically as the other methods.