While this refers to about any car, I mainly have vintage muscle cars in mind with this.

What made Chrysler think “This engine should be 426 ci” Why not 425? 427?

What made GM think “This engine should be 350 ci” Why not 349? 351? 879?

I see that around the 7.0L mark was common (Ford/Chevy 427, Chrysler 426, Ford 428/429)

Also the 7.5-ish L mark (Olds/Pontiac/Buick 455, Chevy 454, Ford 460)

I must say, the numbers “427” and “454” do roll off the tongue quite well.