40 CFR 89.117 - Test fleet selection.
(a) The manufacturer must select for testing, from each engine family, the engine with the most fuel injected per stroke of an injector, primarily at the speed of maximum torque and secondarily at rated speed.
(b) Each engine in the test fleet must be constructed to be representative of production engines.
(c) After review of the manufacturer's test fleet, the Administrator may select from the available fleet one additional test engine from each engine family.
(d) For establishing deterioration factors, the manufacturer shall select the engines, subsystems, or components to be used to determine exhaust emission deterioration factors for each engine-family control system combination. Engines, subsystems, or components shall be selected so that their emission deterioration characteristics are expected to represent those of in-use engines, based on good engineering judgment.