Kevin
Hi Danylo.
What Titan says is correct but you've only just started and you're in a two car league. The competition in Rookie is unlikely to be very strong and if you change engines for both cars every race you're going to need to spend an average of 1 token per race to purchase additional engines over and above those provided by the game.
IMHO at your level in a Rookie tier there are more important things to spend your tokens on. So until the competition becomes stronger I would change engines every other race.
Couldn’t agree more. In most leagues you can get through Rookie and Pro changing engines every third race.