Any engine will perform better after time.
Some engines take around 20k to 25k before max power, fuel economy and smoothness are reached. It is gradual so most people never notice.
For proof check one-year test on vehicles. They should give speed numbers at the start and end of test. I've seen the 0-60 knocked down one second before but that is an exception.
Engines are like fine wine (atleast to a point)