A suggestion I have been thinking about myself as well as discussing with some people in my league.
I am sure this will get rejected but here goes.
Allow each team to field up to four or five cars if their finances, spare parts and engines permit it.
This is because I have some teams in my league with lots of money, parts and maxed facilities due with the capacity to run 3-5 cars in each race, but other teams struggling with very little money, poor facilities and not enough spare parts to repair each car for each race.
Based upon this, it is clear that the smaller teams would be better off only being able to run one car each race and not drain their resources as much, allowing them to upgrade facilities and close the gap to the bigger teams.
The bigger teams could also aid to closing this gap by running three or more cars in each race, draining their money and parts more.
Essentially what I am suggesting is an IndyCar style league where the biggest teams can run four cars and the smallest run a single car. This idea is somewhat influenced by my enjoyment of IndyCar as a series.