Section 1042.230 - Engine families(a) For purposes of certification, divide your product line into families of engines that are expected to have similar emission characteristics throughout the useful life as described in this section. You may not group engines in different engine categories in the same family. Your engine family is limited to a single model year.(b) For Category 1 engines, group engines in the same engine family if they are the same in all the following aspects:(1) The combustion cycle and the fuel with which the engine is intended or designed to be operated.(2) The cooling system (for example, raw-water vs. separate-circuit cooling).(3) Method of air aspiration.(4) Method of exhaust aftertreatment (for example, catalytic converter or particulate trap).(5) Combustion chamber design.(6) Nominal bore and stroke.(7) Cylinder arrangement (such as in-line vs. vee configurations). This applies for engines with aftertreatment devices only.(8) Method of control for engine operation other than governing (i.e., mechanical or electronic).(9) Application (commercial or recreational).(10) Numerical level of the emission standards that apply to the engine, except as allowed under paragraphs (f) and (g) of this section.(c) For Category 2 engines, group engines in the same engine family if they are the same in all the following aspects: (1) The combustion cycle (e.g., diesel cycle).(2) The fuel with which the engine is intended or designed to be operated and the fuel system configuration.(3) The cooling system (for example, air-cooled or water-cooled), and procedure(s) employed to maintain engine temperature within desired limits (thermostat, on-off radiator fans, radiator shutters, etc.).(4) The method of air aspiration (turbocharged, supercharged, naturally aspirated, Roots blown).(5) The turbocharger or supercharger general performance characteristics (e.g., approximate boost pressure, approximate response time, approximate size relative to engine displacement).(6) The type of air inlet cooler (air-to-air, air-to-liquid, approximate degree to which inlet air is cooled).(7) The type of exhaust aftertreatment system (oxidation catalyst, particulate trap), and characteristics of the aftertreatment system (catalyst loading, converter size vs. engine size).(8) The combustion chamber configuration and the surface-to-volume ratio of the combustion chamber when the piston is at top dead center position, using nominal combustion chamber dimensions.(9) Nominal bore and stroke dimensions.(10) The location of the piston rings on the piston.(11) The intake manifold induction port size and configuration.(12) The exhaust manifold port size and configuration.(13) The location of the intake and exhaust valves (or ports).(14) The size of the intake and exhaust valves (or ports).(15) The approximate intake and exhaust event timing and duration (valve or port).(16) The configuration of the fuel injectors and approximate injection pressure.(17) The type of fuel injection system controls (i.e., mechanical or electronic).(18) The overall injection timing characteristics, or as appropriate ignition timing characteristics (i.e., the deviation of the timing curves from the optimal fuel economy timing curve must be similar in degree).(19) The type of smoke control system.(d) For Category 3 engines, group engines into engine families based on the criteria specified in Section 4.3 of the NOX Technical Code (incorporated by reference in § 1042.910 ), except as allowed in paragraphs (e) and (f) of this section.(e) You may subdivide a group of engines that is identical under paragraph (b) or (c) of this section into different engine families if you show the expected emission characteristics are different during the useful life. However, for the purpose of applying small-volume family provisions of this part, we will consider the otherwise applicable engine family criteria of this section.(f) You may group engines that are not identical with respect to the things listed in paragraph (b), (c), or (d) of this section in the same engine family, as follows: (1) In unusual circumstances, you may group such engines in the same engine family if you show that their emission characteristics during the useful life will be similar.(2) If you are a small-volume engine manufacturer, you may group any Category 1 engines into a single engine family or you may group any Category 2 engines into a single engine family. This also applies if you are a post-manufacture marinizer modifying a base engine that has a valid certificate of conformity for any kind of nonroad or heavy-duty highway engine under this chapter.(3) The provisions of this paragraph (f) do not exempt any engines from meeting the standards and requirements in subpart B of this part.(g) If you combine engines that are subject to different emission standards into a single engine family under paragraph (f) of this section, you must certify the engine family to the more stringent set of standards for that model year. For Category 3 engine families that include a range of maximum in-use engine speeds, use the highest value of maximum in-use engine speed to establish the applicable NOX emission standard. 73 FR 37243 , June 30, 2008, as amended at 75 FR 23001 , Apr. 30, 2010