FMSCA Regulation 325.51
325.51 Scope of the rules in this subpart.
(a) The rules in this subpart specify conditions and procedures for measuring the sound level generated by a vehicle when the vehicle's engine is rapidly accelerated from idle to governed speed at wide open throttle with the vehicle stationary, its transmission in neutral, and its clutch engaged, for the purpose of ascertaining whether the motor vehicle conforms to the Standard for Operation Under Stationary Test, 40 CFR 202.21.
(b) The rules in this subpart apply only to a motor vehicle that is equipped with an engine speed governor.
(c) Tests conducted in accordance with the rules of this subpart may be made on either side of the vehicle
