Stroker Engine Science: A Detailed Explanation

Stroker Engine Science: A Detailed Explanation

If you’re here and you’re reading this story, there’s a good chance you already know what a stroker engine is, but if you don’t, it is, in the most basic of terms, an engine featuring a crankshaft with a larger stroke (deeper journals) than was factory for any given engine. By increasing the stroke, the piston travels further in the cylinder, thereby increasing the displacement of the engine and altering the combustion process to produce more horsepower.

Beyond that basic explanation, there is a considerable amount of science that goes into developing and spec’ing the internals for an engine with an increased crankshaft stroke. As you can see illustrated in the video below, while the piston reaches the top of the cylinder at precisely the same time using stroker and standard-length crankshafts, the increased stroke length results in a faster piston speed. This becomes a key point for engine builders, because this can cause RPM limits to be approached. Power loss can also result.

There is tremendous force on not only a crankshaft, but particularly on the piston, rod, and wrist pin during the stroke and combustion process, as the piston and rod assembly is traveling at the equivalent of more than several thousand feet per minute, decelerating to zero at top-dead-center and bottom-dead-center, and accelerating again. As you increase the stroke, there is an increase in both the mean and average piston speed (the piston travels at different speeds during a full revolution, depending on rod angularity — the rod length to engine stroke ratio), even without increasing the engine RPM. Increase the engine RPM, as racers and hot rodders often do, and you further increase piston speed and the demands on the rotating assembly.

A stroker engine at left — note the rod and piston bottom-dead-center point lower in the cylinder and its higher speed on the upstroke and downstroke

Our friends at Race Winning Brands, which market such brands as Wiseco, JE Pistons, Diamond Pistons, K1 Technologies, Trend Performance, MGP Connecting Rods, and Dart Machinery, understand this relationship as well as anyone in the industry, and they’ve developed parts and pieces in tandem designed to cope with this harsh environment. Its team put together a highly informative article on the science of stroker engines, complete with formulas for calculating piston speed, inertia forces, and a whole lot more. 

Visit the Wiseco Performance Products blog to give the story a read!

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