Stroker Kit

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A Stroker kit is an aftermarket assembly that increases the displacement of a Reciprocating engine by lengthening the stroke of the piston. This is done by using a different crankshaft where the connecting rods have a greater radius to the axis of rotation of the crankshaft. While this increases displacement and torque it can potentially lower the limit to which the motor can rev safely compared to the stock configuration. The main advantages of using a stroker kit when rebuilding an engine are that one won't have to change to a larger engine block to significantly increase displacement and one can retain many existing parts from the previous engine.

A typical complete stroker kit is comprised of the crankshaft, connecting rods, pistons, piston pins, main bearings, rod bearings, and piston rings. This assembly is also called "the rotating assembly" or "the bottom end". Many different types of each of the components can be used for different applications. Crankshafts, for example, may be either of forged or of cast manufacture, and pistons may be forged or cast, with different methods of casting, including a process producing a part called a hypereutectic piston. Rods may consist of I-beam or H-beam rods.

[edit] Differences from OEM configurations

Two key characteristics differentiate stroker kits from OEM rotating assemblies. First, and most important, the crankshaft's rod journals are physically farther from the main journals than on the original equipment. A given extension in the distance between the rod and main journals results in twice that distance in increase of piston travel. For example, in a Chrysler LA (1971-1992) 360 cubic inch V8, the rod journal centerline is 1.79" from the main journal centerline. The piston travels 3.58" in this configuration. When this engine is modified with a 402 cubic inch stroker kit, the distance between the main journal centerline and the rod journal centerline is increased to 2.00", which results in the piston travelling 4.00". So, the modified crankshaft with 0.21" further distance between the main and rod journals results in 42 cubic inches of displacement greater than the engine had before.

The second key characteristic of a stroker kit versus OEM is the location of the piston pin and the top of the rod within the piston, or the compression height. The stock Chrysler LA engine in the example above has a main to rod bearing centerline distance of 1.79", a rod that is 6.123" long, and a piston that is 1.67" from piston pin centeline to top, depending on the application. As the engine stroke is increased in the example above, the 402 cubic inch configuration would place the piston 0.21" higher in the cylinder at top dead center, and with a distance of 9.585" from crankshaft main centerline to deck, the piston would protrude about 0.21" higher than the top deck, or would collide with the cylinder head combustion chamber. To offset this, aftermarket pistons relocate the piston pin higher within the piston itself. This change in compression height leaves the piston with 1.462" of material in the top portion of the piston, instead of 1.672" as is stock.