The driving force of car engine sizes is “tax brackets”. Worldwide, governments set stepped tax thresholds such as “below” 1.0 or 1.5 or 2.0 or “above” 3 litres etc., with duty and other taxes increasing accordingly.
These steps guide markets in terms of pricing and sales targets, and cascade through everything from tax to insurance categories and company car entitlements to motorsport classes and licensing authorities.
So for any particular model of car, engine designers are given a whole list of technical requirements and performance targets…within a size ceiling. They will aim for that, get as close to it as possible, but make sure they don’t exceed it. And unless they are making something for an entirely new manufacturing plant, they will consider existing component production lines (and what can be out-sourced or is already available without additional plant and equipment time and costs) among many other parameters to deliver the required result.
Throughout the industry, different models (and even different makes) share many identical components. I once replaced the pistons on a 1963 six-cylinder Mercedes with parts made for a 1980s four-cylinder Ford.
Of far greater importance than a “round” number on engine size is that 1,999 does not emerge as 2,001 – because although that will make no discernible difference to the engine’s output (or weight or shape) it could make a significant difference to the car’s price. In mass production, genius is not about achieving the ideal – it is about making the best compromises. And it does not make minor design changes that could have major cost consequences.
