Just a few idea’s of mine that I would like to see, I don’t expect a reply from the clever blokes making this game as I’m sure your very busy 
- Different turbo sizes, multiple turbo’s, PSI adjustments
- Different superchargers, roots, twin screw, centrifugal and again different sizes (i.e. 6/71 to 14/71) as well as PSI adjustments (i.e. 5psi to 40psi) and why not perhaps stacking two roots superchargers onto of each other? More of a show off thing rather than actual performance.
- Carb and Injected superchargers and turbo’s
- Superchargers polished, teflon etc.
- Different styles and sizes of air filters for on top of supercharger, also a range of “hats” hilborn scoop, bug catcher, bird catcher, big 'n ugly, shotgun scoop, JBR four blade hat
- Big block ford engines and big block chev engines capable of massive capacity (i.e. 632ci)
- Nitrous, different size shots (i.e. 100hp to 500hp) wet systems, dry systems, multi-port fogger, carb plate fogger
- Wheelie bars, spoilers, bonnet scoops
- Wheel tubs for drag racing
- Adjustable manifold height (i.e. selective tunnel ram height) even with supercharger, it would be good to have wild look with an already tall manifold
- Different carb sizes (i.e. 400cfm to 2000cfm)
- C10, C12 racing fuel as well as methanol
- Supercharger restraints
As you can tell im focused around engine customization 
Thanks guys looking forward to the result