For the purpose of this, I've assumed you already have GP2Edit to edit and export carsets. In case you don't, you can get it directly from here:
http://www.smyoung.fsnet.co.uk/gp2ed186.exe
The approach I'm suggesting here is adjusting the power of all teams simultaneously. That way, all AI's engines will appear stronger, however, the balance between the teams that has already been established in the carset you got will stay intact.
This is just for illustration - here you can see where every team's power and reliability values are located normally, if you select them one by one from the main screen. Now, if you select "Performance > Cars" from the list of menues above, you can edit all the teams' values simultaneously with this dialogue:
If you work with the stuff inside the red frame that I added to this picture, you will notice that every time you click on the "+" sign, all teams' power settings increase by the number specified.
I think this is the easiest change that does not compromise the balance between the teams (i.e. Ferrari being stronger than Toro Rosso). If you want to get more complicated, you'd have to get into the individual tracks' files (like a Monza.dat in your circuits directory) and edit the CC setup. It will most likely also have an effect, however, I've never done that, so I can't get you any instructions for that.
If I understand your concern right, whether the cars "break" or not does not depend on the car's power settings, but their failure probability (I've made a green frame around these settings in the screens). The greater this value is, the more likely any cars are going to retire from the race because of a technical failure - provided you have technical failures activated in the driving options dialogue within the game.
WOW, very awesome!
