Siamesed cylinders are engine cylinders arranged in such a way that they have no channels between them to allow water or other coolant to circulate.[1][2]
Cylinders are generally arranged in this manner when the engine block is of limited size or when stability of the cylinder bores is of concern, such as in racing engines.[3] The advantage is that the engine block will be reduced in size, or the bore can be increased in size. The disadvantage is a higher temperature between two cylinders, requiring a stronger engine block to avoid distortion of the metal, and better gasket sealing between the two bores.[1]