40 CFR § 1068.415 - How do I test my engines/equipment?
(c) Test at least two engines/equipment in each 24-hour period (including void tests). However, for engines with maximum engine power above 560 kW, you may test one engine per 24-hour period. If you request and justify it, we may approve a lower testing rate.
(d) For exhaust emissions, accumulate service on test engines/equipment at a minimum rate of 6 hours per engine or piece of equipment during each 24-hour period; however, service accumulation to stabilize an engine's emission levels may not take longer than eight days. The first 24-hour period for service accumulation begins when you finish preparing an engine or piece of equipment for testing. The minimum service accumulation rate does not apply on weekends or holidays. We may approve a longer stabilization period or a lower service accumulation rate if you request and justify it. We may require you to accumulate hours more rapidly than the minimum rate, as appropriate. Plan your service accumulation to allow testing at the rate specified in paragraph (c) of this section. Select operation for accumulating operating hours on your test engines/equipment to represent normal in-use operation for the family.
(e) Test engines/equipment in the same order you select them.
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