I am currently working on performance mods.
My first is a 'not created equal' mod, where I readjust the starting conditions of cars (including fuel consumption) and allow the updates to the car to be randomised slightly too, so that each upgrade isn't equal (and thus, final car positions are unknown).
For this though, I am carefully testing (and comparing) performance tweeks to ensure nothing goes too overpowered this is gonna take a few days.
My end goal is to make it so you can have Major Perfermance Changes (including new and rearranged engines) in different seasons (though you will probably have to come out the game and overwrite your files manually at the end of each season, but that isn't a big deal).
But, there is little problems to make performance completely equal, or severely close the gap between cars. What were you hoping for exactly. Because there are limitations such as - I believe - your team expectations won't change as the RnD screens don't recognise changes in performance (it's just a number that goes up)