Flat-plane crank

The flat-plane crank (sometimes flatplane) is a type of crankshaft for use in internal combustion engines that has a 180 degree angle between crank throws.[1]

Flat-plane cranks are used in V-configuration engines, generally with eight cylinders.[1]

Computer generated image showing the major internal moving parts of an inline-four engine, including the flat-plane crankshaft.

Inline-four cylinder engines almost all use flat-plane cranks, and thus are not usually identified as such. However, there are a few exceptions with crossplane cranks.

Front view of a V8 flat plane crankshaft with corresponding connecting rod positions

The flat-plane crankshaft is a design that is no longer used in most mass production road cars as it is more prone to vibration and is inherently much louder than a crossplane crankshaft. However, due to its simpler construction requiring less counterweight, it is inherently lighter with a higher rev limit. For this reason, it remains useful in sports and racing cars.[1] Flat-plane crankshafts are generally associated with European sports cars such as Ferrari and Lotus V8 engines, and cross-plane cranks with American manufacturers. There are some exceptions such as the Ferrari-designed crossplane crank V8 of the Lancia Thema 8.32 and the flat-plane crank Ford Mustang GT350. [2]

The way in which a flat-plane works within a V8 engine is more like two in-line 4-cylinder engines mated together,[1] with the firing order of each order being in a Right-Left-Right-Left-Right-Left-Right-Left pattern.[3] Being in this in-line configuration allows for the engine to rev much faster, making it more suitable for racing engines.

References

1. "What Is A Flat-Plane Crank And Why Is It So Loud?". Retrieved 19 April 2016.
2. "Full text of "Motor January 2016"". Retrieved 19 April 2016.
3. Clark, John. "Flat Plane Crank". Projectm71. Retrieved 3 May 2019.