4. Max Category - Engine

You can swap engines as long as the engine goes in the same end of the car, and stays transverse/longitudinal as the OE car came with. The engine you swap in also needs to come from a production automobile.

What you do to your engine will affect your class - modified naturally aspirated engines go up one class, unmodified single-unit forced-induction engines go up one class, and any multi-unit or modified forced induction goes up two classes.

For example, if you swap in a "stock" naturally-aspirated engine into your car you go into the class with "unmodified" limits. If that engine comes with a single-unit forced induction or you build that naturally-aspirated engine, you go up one class. If you modify or add forced induction or it comes with twin-turbos, then it goes up two classes.

Max Category Engines - Full Rules

1. Allowed Engine Modifications
Components (internal and external) may be modified or replaced, other than the following restrictions:

A. Engines must be derived from production automobiles. Motorcycle, snowmobile, marine or other engines of non-automobile design are not permitted.

B. The engine orientation and the general engine bay location must not be changed from OE. (E.g., Vehicles with transverse engines may only install an engine in a transverse orientation, vehicles with longitudinal engines may only install an engine in a longitudinal orientation, front-engine stays front-engine, rear/mid-engine stays rear/mid-engine.)

Max Category Engine Modification - Definitions

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.