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A stroker kit is used to produce more power from an internal combustion engine by increasing its displacement. Consisting of a crankshaft, pistons and connecting rods, the stroker kit is installed as a complete unit. The stroker kit is created by offset grinding the crankshaft's rod journals. This is combined with connecting rods often designed for a different manufacturer's engine, such as using Chevrolet connecting rods in a Ford engine. Pistons are typically custom manufactured to fit the specific application and requirements of the stroker kit.
Primarily used in racing applications, a stroker kit provides the power typically found in a larger engine while maintaining the weight of a smaller engine. A stroker kit is often used in drag racing car engines because it is an effective lightweight alternative to building a heavier, more powerful engine. By using a stroker kit, displacement numbers typically found only in heavy big block engine configurations can be achieved in much lighter, small-block engine packages.
Installing a stroker is more involved than simply bolting in new parts. In most stroker assemblies, the engine block must also be cleared in order to facilitate the longer throws of the stroked crankshaft. The clearancing procedure involves grinding the bottom of the cylinder walls to avoid contact between them and the spinning crankshaft and connecting rods. Failure to adequately clearance an engine block will result in catastrophic engine damage and failure as the crankshaft, connecting rods and engine block all meet upon engine start up.
Increased oil consumption is often a negative side effect of building a stroker engine. Often the piston pin is placed very high in the piston, actually placing it within the piston rings. This can cause the oil to slip past the rings and cause an oil burning problem in some engine designs. Excessive piston rock can also create oil consumption. The longer stroke also has a negative effect on the angle in which the connecting rod finishes and begins the stroke, causing the piston to rock in the cylinder bore.
The increase in stroke also adds torque to an engine. In a racing application, the stroker kit equates to a vehicle leaving the starting line or exiting a corner with more power. The unfortunate side effect of a stroker kit lies in the initial added cost not only of the rotating assembly, but also of the machine work required to make the engine and kit compatible.