what does intake restrictions and voluntary mass specifically do?

Intake restriction reduces the power/torque output of the engine. Added mass puts more weight in the car (like success ballast). In certain applications you can create 2 or more "classes" using a single car by varying the intake restriction and/or added mass. For example, an unrestricted FZR could be considered a GT1 car. An FZR with 20% intake restriction could be considered a GT2 car.

If you go into the garage and start changing the intake restriction/added mass/added mass position sliders you should see the power/torque/total mass/weight distribution values updating live.

thanks for the explanation