Hey there jose.
I see you are in a 100% distance no refuelling league.
So the first thing I would suggest you think about fuel.
Check your race reports for your drivers and see how much fuel they are finishing the race with. If you were perfectly fuelled, they would finish with less than 1L (difficult to achieve, but any excess fuel you are carrying is excess weight through the whole race).
If you are already ok on this front. Then consider increasing your fuel economy. It sounds to me like your opponent may be starting the race with substantially lighter cars and this could be due to fuel levels.