The thinking here is that you don’t need the power and grunt of a six or eight cylinder motor all the time.
So if you don’t need it, don’t use it and save fuel.
If you purchase a new Holden with a V8 Auto you’ll have an Active Fuel Management (AFM) system included.
That’s their name for cylinder deactivation.
It will turn off the fuel injection system in four of the eight cylinders when V8 power is not needed, such as when cruising at low engine revs on the highway.
You won’t feel the change, but you will notice the change in fuel used on the ‘instant fuel’ readout on the dash. It can drop from, say, 11.5 litres/ per 100kms. to a comparable 7.5 litres/ 100kms in 4 cylinder mode.
Of course that doesn’t reflect the overall savings, as Holden suggest that in general day-to-day use it will save you approx 1 litre/100kms.
Chrysler use a similar system for their eight cylinder hemi motors in the 300c and Jeep vehicles – they call it their ‘multi displacement system (MDS)
Honda are the other major players in the market with their ‘unique high tech Variable Cylinder Management’ (VCM)
This is available on the Honda Accord V6 which can run on six, four or three cylinders, resulting in fuel savings and lower emissions.
They claim that the VCM system combines maximum performance and maximum fuel economy.
It runs on 6 cylinders during acceleration and under heavy loads.
But in less stressful conditions it will drop seamlessly back to 4 or 3 cylinders.
For example during cruising it will drop down to just one bank of three cylinders, but with moderate acceleration or higher speed cruising it will ramp up to 4 cylinders.
The VCM system monitors throttle position, vehicle speed, engine speed, automatic transmission gear selection and other factors to determine the correct cylinder activation scheme for operating conditions.