What is unfeasible and silly about tweaking an engine??? It happens in real life, so it must be possible in a game...

Why not make it possible to tweak the engine???
Like lower or raise turbo boost, on turbo cars, more boost makes the engine heat go up and wears the engine over short time, and lower boost makes the engine last longer, maybe...
And tweak of the camshafts intake/exhaust.
Idle rpms and top rpms.
And adjustments for the fuel pump...
Just simple or advanced engine tuning...
And maybe upgrades to buy for the racing credits, turbo, performans upgrades.
And the possibility of changing spoilers or adding spoilers for better looks and traction.