I have some suggestions that I think will make this great game even greater
1- Specific gear ratio s and axel ratios exp ( 3.23 , 2.66. …)
2- Adding a compression tests between couple of cars like a shadow way in the track mode .
3- Adding a compression table between cars like a head to head way .
4- Add 1/4, 1/2, 1 mile track compression between cars.
5- Add camshaft specs in details (durations , lift , loops )
6- Add Drag racing tires
7- Add center exhaust tips
Quick answer: please use the search bar.
Long answer: the game is a tycoon car building game, as such its primary goal is to build and sell cars.
All the parts and tuning suggestions you mentioned are been rejected either due to too much added complexity or not applicable to factory cars. The comparison ideas are not really helpful for a tycoon game.
Except the center exhaust that might be happening.
i might agree on the final drive, of course if the drivetrain production will be in detail eg. for FR layout - gearbox, driveshaft and diff (final drive), thats 3 things to produce, not to count axles, hubs etc.
so why make 2 different final drives, when you can use 1 for a range of engines?