40 CFR §205.157-3

1. (a)A separate vehicle configuration shall be determined by each combination of the following parameters:
   1. (1)Exhaust system (engine): (i) Mufflers; (ii) expansion chambers; (iii) spark arrestors; and (iv) other exhaust system components.
   2. (2)Air induction system (engine): (i) Intake muffler; (ii) intake ducting; and (iii) air cleaner element.
   3. (3)Vehicle drive train: (i) Chain; and (ii) shaft.
   4. (4)Transmission gear ratio: (i) Standard transmission; and (ii) automatic transmission.
   5. (5)Cooling system configuration: (i) Natural air cooled; (ii) liquid cooled; and (iii) forced air cooled.
   6. (6)Category parameters listed in § 205.157-2.
2. (b)[Reserved]