Section 1039.105 - What smoke opacity standards must my engines meet?(a) The smoke opacity standards in this section apply to all engines subject to emission standards under this part, except for the following engines: (1) Single-cylinder engines.(2) Constant-speed engines.(3) Engines certified to a PM emission standard or FEL of 0.07 g/kW-hr or lower.(b) Measure smoke opacity as specified in § 1039.501(c) . Smoke opacity from your engines may not exceed the following standards: (1) 20 percent during the acceleration mode.(2) 15 percent during the lugging mode.(3) 50 percent during the peaks in either the acceleration or lugging modes. 69 FR 39213 , June 29, 2004, as amended at 88 FR 4658 , Jan. 24, 2023