Forced Induction - When the induction is forced by a compressor (Turbo or SC only). Does not include nitrous because nitrous does not force any air.

Power Adder - Increases energy of combustion (adds power but did not force any air/induction) Nitrous is a Power Adder.

N/A - Naturally Aspirated - All this means is that the motor gets its air naturally by sucking it in. IT DOESNT MATTER IF YOU MOTOR IS FULLY BUILD FROM HEAD TO TOE WITH INTERNALS AND BOLT ONS. If the motor sucks the air in on its own, its N/A.

Note : A naturally aspirated car WITH nitrous IS STILL N/A. However it is referred to as N/A WITH A POWER ADDER. This means that the aspiration is still natural by sucking air into the motor, BUT IT HAS AN ADDITIONAL SOURCE OF POWER.

All Motor - These cars must be N/A. They CAN be fully built. They CANT have nitrous. See All Motor Class specs.