2. Engine Modification Definitions
The following criteria is how "modified" or "unmodified" engines are defined for Max Category classing criteria.

A. Modified Combustion Engine
The following criteria are used to define “modification” of an internal combustion engine:

1. Modification or replacement of OE (or OE equivalent) head gasket, head bolts or parts in the valve train, or rotating assembly. (E.g., valve springs, lifters, rockers, camshaft(s), pistons, rods, crankshaft, balance shafts, rotors, etc.) This restriction does not include oil pumps or water pumps.

2. Modification or machining of the engine block, head or rotor-housing beyond factory shop-manual limits.

3. As well as #1 and #2 above, modification or replacement of the following OE (or OE equivalent) parts of a forced-induction engine will be considered modified:

a. Turbocharger, including turbine wheel, turbine housing, compressor, compressor housing, intake manifold and any fastening hardware.

i. Where a non-US market vehicle may not have come with specific emissions equipment (e.g., TGV) forced-induction engines may remove that equipment or, if the ability exists, replace it with a part which does not increase performance relative to the O.E. part. (e.g., TGV deletes which do not increase the diameter or length of the intake.)

b. Supercharger, including housing, phasing gear, rotors, intake manifold and any fastening hardware.

B. Modified Electrical or Hybrid Engine
The following criteria are used to define “modification” of an electrical engine or hybrid drivetrain:

1. Increase in voltage output of electric motors by any means.

2. Change in number, type or discharge rate of OE batteries.