ADR27A

The rule covered "all motor vehicles specified below (see Table 1) equipped with petrol fuelled spark ignition internal combustion engines except those also equipped to use use liquified petroleum gas (LPG) and those with and engine displacement of less than 850 millilitres (850cc), manufactured on or after 1 July 1976.

[2] An amendment was made to the rule affecting vehicles manufactured on or after 1 January 1978 altering the deterioration factor for testing criteria to revised values - refer Criteria The rule was endorsed by the Australian Transport Advisory Council (ATAC), and covered all Australian states and territories.

Maximum permissible limits for each testing criteria were:[1] The rule stated other requirements including:[1] Prior to the release of a new model, manufacturers were required to submit a certain number of new vehicles for testing for each different engine available across a specific model's range.

The rule required manufacturers to introduce emission control systems to the engines of road-registered vehicles on sale within Australia.

As a result, ADR27A-compliant engines generally produced less power than previous non-compliant versions.