The engine size or capacity is generally the amount of the space the combustion chamber displaces and is measured in cc’s as we all are familiar with 220cc, 150cc engines mounted on various bikes.
The engine capacity is measured as Bore x Stroke. Here, Bore is the diameter of the cylindrical block and Stroke is the depth of the cylindrical block, as shown in the image.

The ratio of Bore and Stroke categorize the engine. There are three different types of configuration available depending on the ratio
Short Stroke/Over square Engine: As the name signifies the Stroke is shorter than the Bore. Due to the relatively shorter stroke, the engine revs fast and is more suitable where a quick build of power is important, more importantly where the bikes make power at higher RPMs.
Some examples:
·RTR 180 (62.5mm X 57.8 mm) Bore x Stroke
·Pulsar 220 (67mm X 62.4 mm), 180(63.5mm X 56.4mm) Bore x Stroke
Long Stroke/ Under square Engine: As the name suggests the Stroke is longer than the Bore. Due to the longer stroke, the engine makes good torque at relatively low RPMs. It is important where the bikes’ pulling more (torque) at relatively low RPMs is more important then the top speed.
Some examples:
·Royal Enfield Classic 500 (84mm X 90mm), Classic 350 (70mm X 90 mm)
·Hero Honda Karizma (65.5mm X 68.2mm)
The one the exception to the above rule is the pocket rocket Yamaha R15 (57mm X 58.7mm) which is strange as R15 is a track-oriented bike.
Square Engine: Like a square has both the sides equal, here also the Bore and Stroke is of almost the same size. The engine tries to strike a balance between torque and top speed
Some Examples:
·Yamaha FZ-16 (58mm X 57.9mm)
·Honda Unicorn (57.3mm X 57.8mm)
All these engines have their own advantages and disadvantages and it depends on the rider to decide what kind of motorcycle he/she needs.

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