First Drive: Holden Commodore SS AFM

Review by Feann Torr - 11/March/2009

During a conversation with a friend about where the automotive industry is heading, he pointed out that the media reports a lot of doom and gloom about the future.

That's probably an honest summation. The mood isn't exactly sunny.

But as we speed toward the end of the decade, we're seeing more and more positive changes in the automotive industry.

Hybrid cars are growing in number, affordable electric cars are only a couple of years away and even locally-made cars are starting to incorporate fuel-saving technologies.

We've just spent a week test driving Holden's SS Commodore which is one of the first vehicles in the company's new 'EcoLine' range and the second car in Australia to use cylinder deactivation technology. It comes equipped with AFM or active fuel management which can deactivate four of the eight cylinders to conserve fuel.

All V8-powered Holden vehicles that are specified with the 6-speed automatic transmission now come equipped with the AFM system. The technology is supposed to deliver the power of a V8 with the consumption of a V6, so let's find out how it fares:

I'm sitting at the traffic lights on a Sunday arvo. An XR8 Falcon rolls up and the driver sees the shiny new SS Commodore I'm driving. Naturally I psyche myself up for a full throttle launch.

As the lights flash green I bury the accelerator pedal, confident in the knowledge that this new car takes advantage of cutting-edge fuel saving technology that will allow me to be fast yet frugal.

Unfortunately for lead foots like myself, Holden's new AFM technology doesn't reduce fuel consumption under full throttle.

Where the AFM or active fuel management system works best is when cruising.

So I try this instead: I've just hit an on-ramp to the freeway, I accelerate to 100km/h and switch on the cruise control. The automatic gearbox shifts into 6th gear and then the magic happens - AFM shuts down four of the V8 engine's eight cylinders to reduce fuel consumption.

In essence, the 6.0-litre V8 I was driving had transformed into a 3.0-litre V4 as the fuel delivery system cut fuel to half the engine.

The AFM system is seamless and completely automatic in operation. You don't have to activate it or flick a switch; whenever the car can switch to fuel saving mode, it will.

The V8 Commodore's ECU or engine control unit decides when to switch to 4-cylinder mode and it only switches during very light loads. 

So the burning question is this: does AFM actually result in real-world fuel efficiency improvements?

It does, but only marginally.

When it announced the new AFM system, Holden stated that "the technology can deliver fuel savings of up to one litre per 100 kilometres, with potential for even better results at constant cruising speeds".

After a week of testing we recorded an overall fuel consumption figure of of 13.5L/100km which is about 1 litre per 100km better than our previous efforts, but this involved 75% highway driving with only a few short runs through the suburbs and into town.

We also employed a very conservative driving style and we only applied full throttle a couple of times to test the standing start performance of the vehicle, which was as to be expected despite lower power and torque - very impressive.

Still, this overall figure of 13.5L/100km figure is better than the 14.4L/100km average we recorded when we last tested the SS Commodore, and for a 6.0-litre high performance V8 it's not too shabby.

At times the AFM system works really well, switching to 4-cylinder mode as soon as the car's road speed reached a constant, whether that was 60km/h or 80km/h. However it seemed to be most effective at cruising speeds of 100km/h and above.

"The AFM system is seamless"

Like all Commodores, the new AFM-enabled models are easy to live with and are remarkably practical vehicles with masses of interior space, comfortable seats, a decent turning circle and a cavernous boot.

They're also very easy to drive thanks to the power steering and the trip computer is very effective as displaying a range of different data, especially fuel consumption related information.

The AFM-enabled Holden SS looked like any other performance model in the Commodore range - 18-inch alloys, pumped wheel arches, rear spoiler and all the other sporty trimmings. Small AFM badges on the car's exterior are the only overt signs of the vehicle's technology.

The shift between 8- and 4-cylinder modes is imperceptible, though you can sometimes detect a slight roughness to the engine under acceleration in the 4-cylinder mode.

We once (briefly) managed to get the fuel consumption as low as 7.0L/100km on a flat section of CityLink not far from Melbourne city, which was in 6th gear @ 100km/h. Other times however, the system seemed to be rather moody.

Often it worked well and would drop to 4-cylinders without a hitch - you can tell from one of the trip computer displays when it switches to 4-cylinder mode - but other times it was horribly ineffective (I should point out that we tested a pre-production version so we'll request another model to give the system another test later in the year).

On numerous occasions when the engine switched to 4-cylinder mode there would be virtually no change in fuel consumption. For instance we were cruising at 70km/h with the instant consumption reading 11L/100km in 8-cylinder mode, and when it dropped to 4-cylinder mode it didn't show any change.

Some other curiosities included one situation where we were driving downhill and there was practically no load on the engine yet it wouldn't engage the low emission 4-cylinder mode. Perhaps the car's computer brain had a hangover?

It doesn't take much impetus for the engine to slip back into 8-cylinder mode either. Mild inclines of only a handful of degrees while cruising at 110km/h on the Hume highway initiated all 8-cylinders, for instance.

I think the system would be more effective if the software that controls activation was fine tuned even more for local conditions and it would also be more useful if the car didn't weigh so much. Perhaps Holden will drop the big V8 into an HSV performance version of its new Cruze when it starts building it locally in 2010? Or perhaps not... 

Drivers who order their V8-powered Holdens - whether SS Commodore, Calais, Ute or Statesman - with a 6-speed manual will not benefit from the AFM technology as it's incorporated into the 6-speed automatic versions only.

The 6-speed automatic versions may be less powerful as a result of the technology, down from 270kW and 530Nm of torque to 260kW and 517Nm, but on the road there's not a great deal of difference.

Conclusion

Active Fuel Management technology is supposed to deliver the performance of a V8 with the consumption of a V6, but in reality it's more like the comsumption of a V7. It's not the silver bullet solution to the reducing fuel consumption of large capacity engines, but Holden's AFM is a step in the right direction.

Diesel and hybrid Commodores have probably been shelved in recent times, placed in the 'too costly' bin for the time being, but AFM technology is available now and it shows promise.

The cylinder deactivation technology will buoy interest in Holden's V8 range and though it's not quite as good as the system used in the Honda Accord V6 we tested in 2008, it's better than a poke in the eye with a sharp stick.

There is a lot of doom and gloom surrounding the auto industry at the moment and though the cogs of industry are slow to turn, this is a positive initiative by Holden and will be the first of many intriguing additions to its burgeoning EcoLine range.