§ 86.420-78 Engine families.

(a) The vehicles covered in the application will be divided into groupings whose engines are expected to have similar emission characteristics throughout their useful life. Each group of engines with similar emission characteristics shall be defined as a separate engine family.

(b) Reciprocating families. To be classed in the same engine family, reciprocating engines must be identical in all of the following applicable respects:

(1) The combustion cycle.

(2) The cooling mechanism.

(3) The cylinder configuration (inline, vee, opposed, bore spacings, etc.).

(4) The number of cylinders.

(5) The engine displacement class, § 86.419.