Engines and Chassis have 3 main attributes: Speed, Accel and Turn. These attributes are used by the racing algorithm to calculate the time it takes a car to complete a circuit.
Speed: top speed your car can reach.
Accel: time it takes for your car to reach its top speed.
Turn: how wide or small your car’s turning circle is.
Note: for tracks with too many turns it is recommended to have more Turn than Speed, nonetheless for tracks with few turns but long stretches it is recommended to have more Speed and less Turn.