Engine wear is based on laps (probably) so running a lot of laps on Practice, qualy and race will increase the engine wear, but... besides users asking for it, CM didn't made possible for you to select the engine before a new race, the engine changes are automatic each track. Engine 1 = Race 1, Engine 2 = Race 2 and so on... until all of them have been used them, i BELIEVE it starts the next races with the best engine you have at the moment. You can select another engine when you are in practice. To bad theres no engine scale, so if you want to have a more "realistic" engine wear you need to run lots of laps on practice, qualy and 100% race always. But.... i havent really looked at the engine wear on new races, last year im almost sure that 99% engines went back to 100% on next GP, but 98% or less don't, im going to take a look.