The engine capacity is basically a measure of a cylindrical volume. This is the area of a circle multiplied by height. The problem is that to manufacture something, we tend to focus on linear dimensions like the bore and the stroke. This makes it easier to design the equipment to make the components.
Unfortunately an area of a circle is pi * radius^2. Since pi is irrational, it is not really feasible to form a circle with a rational linear dimension (like a radius of 88mm) and come up with a “nice” number for the area.
Thus, the volume is not going to be a “nice” number either.
I suspect it’s partly due to the way governments assess vehicles for licensing/tax fees with different rates for engine capacity. The thresholds might be at, say 1L, 1.5, 2, 2.5, 3 etc. The manufacturer will design the engine to be under a threshold to make it cheaper to own.
There may also be government fees for pollution (NOx) and CO2 emissions, and the ECU (engine management computer) can be tuned to limit the performance to reduce the cost of ownership.
When I was a teenager I had a motorbike which had a 125cc engine, because that’s all I could legally ride at my age. As it happened, it turned out to be a 150, but nobody ever knew, except me and a mechanic who once rebuilt the engine after a bearing failed.
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