05 May, 2008

Engine Profile

We can describe the engine's configuration in several aspects, be it from the head where people speaks of DOHC (dual overhead cam) or SOHC (single overhead cam) or the cylinder layout - parallel twin, V-twins, inline four, V-four, triples, boxer, etc. There is also the other which relates to the engine capacity - bore and stroke.

There is a bore to stroke ratio which can describe the characteristic of the engine.
For the Hayabusa with a bore of 81mm and 63mm stroke,
the bore/stroke ratio is 81/63=1.285

This number is more than one. This is known as an oversquare engine or a short stroke engine.

For those with ratio that is less than one. That is known as a undersquare engine or a long stroke engine

For bore/stroke ratio of 1 (or commonly, from 0.95 to 1.04) it is also referred to as square engines.



Pros - Less stress on crankshaft, more reliable, better for high speed, less wear
Cons - Lower torque at low end compared to the counterparts, cannot run as high compression ratio, poorer fuel economy, tendency to overheat, wider in engine dimension


Pros - Higher low end torque, can have higher compression ratio with the same octane fuel, lesser tendency to overheat
Cons - Greater friction and stress on crankshaft, smaller bore results in smaller valves thus restricting gas exchange, lower redline

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