Engine and exhaust modifications

An alternative engine may be fitted to replace one that is no longer serviceable or to achieve an increase in capacity, power and torque.

If the engine in your vehicle has been changed with no modification and is an available option or standard specification for your vehicle make, model and year, complete MR7 Application to Alter vehicle or trailer details (185.6 KB PDF) form and submit it to Service SA for approval.

If approved, you will notified of the change.

Engine changes statement of requirements

Before installing an engine of greater capacity than the one originally supplied, a statement of requirements must be obtained.

When assessing an application the following factors will be considered:

  • weight
  • power and torque output in relation to braking
  • strength of the vehicle
  • effect on steering and suspension components
  • the effect on vehicle handling.

A Statement of Requirements can be obtained by submitting MR620 Application to Modify a Motor Vehicle (891.8 KB PDF) to Vehicle Standards.

Certificate of exemption

After the modified vehicle has passed a roadworthy inspection a certificate of exemption will be issued to the registered owner.

This certificate of exemption must be kept in the vehicle and produced upon request by a police officer or authorised inspector.

Emission requirements for passenger vehicles operating on petrol

Vehicles manufactured on or after 1 January 1972

Vehicles manufactured on or after 1 January 1972 must comply with Australian Design Rule (ADR) 26, including:

  • Vehicles must be fitted with an operational positive crankcase ventilation valve (PCV).
  • The exhaust system must not emit more than 4.5% carbon monoxide at engine idle speed.

Vehicles manufactured on or after 1 July 1976 to 1 January 1986

Vehicles manufactured on or after 1 July 1976 to 1 January 1986 must comply with either ADR 27A, 27B or 27C, including:

  • A carbon canister must be fitted, operational and connected to the fuel tank and induction system.
  • The vehicle must also be fitted with sealed engine rocker cover(s), regardless of engine fitted, vented through the engine's induction system.
  • Vehicles must not emit more than 4.5% carbon monoxide and 250 parts per million of hydrocarbons at engine idle speed.
  • Per ADR 27A, vehicles must not emit more than 2.5% carbon monoxide and 250 parts per million of hydrocarbons at engine idle speed.

Vehicles manufactured on or after 1 January 1986

All vehicles manufactured on or after 1 January 1986 must comply with ADR 37, including:

  • This category of vehicle may only be fitted with an engine complying with ADR 37 or later ie an engine designed to operate only on unleaded fuel), which incorporates all associated emission control components.
  • Fitting an engine other than an original or optional engine requires approval from the Department for Infrastructure and Transport.
  • No alterations to the engine's camshaft, inlet manifold, carburettor/fuel injectors, engine control unit or the catalytic converter are permitted.
  • Airflow meters must not be disconnected.
  • Modified or aftermarket plenum chambers or throttle bodies are not permitted.
  • Extra or larger fuel injectors or variable fuel pressure regulators are not permitted.
  • If the vehicle was originally fitted with a catalytic converter by the manufacturer, the vehicle must continue to operate with one.

Passenger car derivatives - panel vans and utilities under 4.5 tonne GVM

The requirements for passenger car derivatives manufactured on or after 1 July 1976 are identical to those for passenger cars.

For vehicles manufactured prior to this date there are no requirements except for positive crankcase ventilation (PCV).

Exhaust systems and noise

Modifications to exhaust systems are permitted if they do not conflict with the requirements of any other rules or regulations.

Vehicles also must meet the following requirements:

  • Vehicles may be fitted with extractors provided that any emission control devices which were originally fitted to the original manufacturer's exhaust system, including catalytic converters, are re-connected and operational.
  • The extractors must not foul any part of the steering, suspension, braking or fuel systems.
  • Catalytic converters and exhaust sensors that have been replaced are to be positioned in the same exhaust flow location as in the original system.
  • The exhaust outlet exit must be behind the last door or window opening on the side or rear of the vehicle.
  • The exhaust outlet must be as close as possible to the outer edge of the vehicle, but not outside or underneath the vehicle.
  • If the exhaust system is not underneath the vehicle and can come into contact with people, it must be shielded.
  • The exhaust outlet must extend at least 40 mm beyond the furthermost outboard or rearmost joint of the floor pan that is not continuously welded or permanently sealed and which could permit direct access of exhaust gases to the passenger compartment, but not beyond the perimeter of the vehicle when viewed in plan.
  • The side exhaust outlet must discharge to the right hand side of the vehicle and downwards at an angle between 15 degrees and 45 degrees from horizontal.
  • The exhaust outlet, if to the rear of the vehicle must discharge at not more than 10 degrees above or 45 degrees below the horizontal.
  • The vehicle must have 100 mm ground clearance.

Extractors and aftermarket exhaust systems may be fitted provided that the sound levels specified in the Road Traffic (Light Vehicle Standards) Rules 2013 Rules are not exceeded.

For passenger cars, passenger car derivatives and panel vans manufactured:

  • before 1 January 1983, the stationary noise level when tested must not exceed 96 dB(A)
  • on or after 1 January 1983, the stationary noise level when tested must not exceed 90 dB(A).

Contact DIT Vehicle Standards

Related information

Other websites

Australian Design Rules - Australian Government Department of Infrastructure, Transport, Regional Development and Communications


Road Traffic (Light Vehicle Standards) Rules 2013

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Page last updated 23 September 2020

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