In these days of increased environmental awareness it’s only a matter of time
until car manufacturers and car owners are pressured to, literally, clean up
We’ve seen the local car industry put through hoops twice in the last 30-odd
years – first with the introduction of ADR27A and again with the adoption of cat
converters and unleaded fuel. And there’s more to come.
In the first of this two-part series we’ll focus on ADR 27A – the equipment
required and its impact on fuel economy and power...
The ‘70s Shake-up – ADR 27A
In mid 1976, the federal government introduced ADR (Australian Design Rule)
27A in an attempt to reduce car emissions.
ADR 27A requires that each car built from July 1st, 1976 be fitted with a positive
crankcase ventilation system, an evaporative emission control system and an
exhaust gas recirculation system. As far as we’re aware, there were no specific
emissions levels that had to be achieved – all a manufacturer had to do was
install the specified equipment.
So how does ADR 27A related equipment reduce emissions, you ask?
Well, the PCV system reduces the amount of unburned crankcase hydrocarbons
that are released to atmosphere by redirecting these hydrocarbons into the
combustion chambers. The contemporary Ford XC Falcon (like many other vehicles)
employs a system that draws fresh air from the air cleaner assembly into the
crankcase via a passage in the oil filler cap. This fresh air mixes with
crankcase vapours and is drawn into the combustion chambers through a PCV valve
that connects to the carburettor throttle body. For efficient operation, the PCV
valve must function properly and the crankcase must be sealed (no leaks at the
dipstick or oil filler).
The next part of the ADR 27A arsenal is an evaporative emission control
system; approximately 20 percent of all hydrocarbon emissions are caused by
evaporative losses from the fuel tank and carburettor. The mid ‘70s Ford Falcon
employs an ‘absorption-regeneration’ system which temporarily stores evaporated
fuel vapour inside a charcoal canister.
The vapour stored in the charcoal canister is received from the fuel tank and
carburettor float bowl. When the engine is started, stored vapour is drawn into
the combustion chambers – and the charcoal canister is then again ready to receive
more vapour. Effective evaporative emission control requires that fuel filler
cap is sealed to prevent vapour escaping to atmosphere.
Exhaust gas recirculation is one of the most important elements of ADR 27A.
In the ‘70s Ford, the exhaust gas recirculation (EGR) system delivers up to 15
percent of the inhaled air-fuel mix. The aim is to reduce peak combustion
temperature and reduce the fresh air-fuel mix in the combustion chamber. The
Ford system feeds exhaust gas into the carburettor’s primary bores via a
vacuum-operated EGR valve. The EGR valve is linked to a heat-sensitive ported
vacuum switch which avoids driveability problems when the engine is cold.
In addition to these vital ADR 27A components, the mid ‘70s Ford Falcon also
uses a controlled combustion system (CCS). CCS controls the temperature of
intake air to help maintain effective air-fuel combustion and improve economy. A
thermostat (which is mounted inside the air cleaner assembly so that it always
‘feels’ intake air temp) is used to control a flapper valve in the air cleaner
assembly. Under direction of the thermostat, the flapper valve draws warm air
from the exhaust manifold(s) when the intake air is cool and switches to draw
under-bonnet air when the thermostat senses warm intake air temperature. A
similar arrangement (sometimes referred to as a heat riser) can be found in
other contemporary cars.
So that’s the equipment that ADR 27A brought – what was their real-world
Unfortunately, we can’t make a back-to-back comparison between Ford engines
with and without ADR 27A equipment because there were numerous other engine
changes made at the same time. The popular 250ci (4.1 litre) six-cylinder was
changed to a cross-flow design and the 302ci (4.9 litre) V8 was upgraded with a
4-barrel carburettor to counteract any ADR 27A-related loss of power.
But a substantial increase in fuel consumption was unavoidable – all ADR 27A
compliant Ford engines consume about ten percent more fuel than previously.
Interestingly, we have not seen any figures to show an improvement in
Ford’s local rival, Holden, struggled even more with the adoption of ADR 27A.
Holden’s first ADR 27A compliant bread-and-butter model was the HX Kingswood.
For the HX, Holden dropped the existing small capacity six-cylinder engine and
focussed on the bigger 202ci (3.3 litre) six, 253ci (4.2 litre) V8 and 308ci
(5-litre) V8s. In ADR 27A guise, the 3.3 litre six produced 88kW (down from
99kW), the 4.2 litre V8 made 120kW (down from 136kW) and the big 5-litre V8
managed only 161kW (down from 191kW). Compression ratios remained virtually the
same during the transition to ADR 27A spec – it was the newly introduced
emissions equipment that was causing an across-the-board power drop of up to 15
Unfortunately, the breathless ADR 27A Holden engines also consumed more fuel
than previously. Like the Fords, fuel consumption increased by approximately ten
So while ADR 27A was successful in reducing certain types of vehicle
emissions, its overall benefit –
when considering increased fuel consumption, reduced engine power and extra
manufacturing to produce the equipment – is questionable.
ADR 27A Related Problems
ADR 27A equipment isn’t completely service-free as many people seem to
PCV valves, EGR valves, clogged hoses and failed seals are quite commonly the
cause of driveability problems in poorly maintained cars. This is particularly
the case where the engine is worn and producing excessive amounts of blow-by –
it’s common for the PCV valve to fail, intake filters to clog and spark plugs to
Faulty exhaust gas recirculation systems can also aggravate a situation where
the engine is already running close to detonation. This has become a real issue
for cars that are designed for leaded fuel but have been forced to run on lower
Stick around for Part Two of this series – we’ll look at the introduction of
cat converters and unleaded fuel, the latest emission standards for new cars as
well as ongoing emission checks!