If you take a quick survey of the automotive world, you’ll find a great number of vehicles powered by a 2.0-liter inline-four-cylinder engine. And if you look a little deeper, you’ll find something even more curious.

Not only have 2.0-liter I4s become ubiquitous among reasonably-priced models, but it seems the engine’s format of (very close to) 500cc per cylinder has taken over the rest of the industry. The 3.0-liter V6, the 4.0-liter V8, the 5.0-liter V10, and the 6.0-liter V12 are all extremely common displacements and all have 500 cc (or so) cylinders .

Why does that seem to be all there is on the market? Because it’s very good at what it does. The format is among the best at creating good power and DriveTribe’s Mike Ferny spoke to Bruce Wood, the Managing Director of Cosworth to find out why.

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Displacement of 500cc per cylinder is a bit of a Goldilocks figure of “Not too big, not too small,” says Wood. If you go much smaller than that, you end up with a high surface area to volume ratio. That allows too much of the flame’s heat to come into contact with the cylinder walls and to cool down, effectively warming up coolant rather than pushing the cylinder.

Too far the other way, though, and you can end up with a flame front that doesn’t reach the walls of the cylinder. With a gap between the explosion and the cylinder wall, that can lead to bad emissions. The 500cc number isn’t set in stone, though.

“So 500 isn’t a magic number, it’s not like if you go to 499 it’s not going to work,” says Wood. “But in that kind of high 400s, low 500s works very nicely. Which is to say that it’s neither too big nor too small for nearly every application.

Moreover, having regular cylinder sizes works very well for automakers that are always looking for production efficiencies across their entire range.

So there you have it. Engines tend to be 500ccs per cylinder because it’s just right.