Running on empty well worth the cheeky wager

Driving a box-stock Commodore V6 almost 1000km from Auckland to Christchurch on one fill is not to be sneezed at, writes DAVE MOORE.

They said it couldn't be done, and I must say that I had doubts most of the way down both islands, as part of Holden's "One Tank Challenge". But a small wager was set, and I decided I'd give it a go.

The idea was to drive one of Holden's SIDI-engined V6s from Auckland to Christchurch on a single tank of petrol, without dawdling and with the air-conditioning on. Not difficult in a modern diesel perhaps, or a supermini-sized car, but in a big Commodore sedan? You have to be kidding.

We also had to go two to a car with luggage and work gear, which meant the OTC became a real-world task and not an artificial one. We were set pretty brisk average speeds, too – with penalties – so we often had to compensate for town and city snarls by driving at the legal open-road limit to make up time.

So we didn't hang around at any stage, though we all had palpitations at road works, minor traffic stops and, of course, manoeuvring onto and off the Interislander.

It was soon obvious that our Commodore, an SV6 of 3.6 litres, was happiest in cruise control on long flat straights, with between 1350rpm and 1600rpm on the tacho, depending on the average speed required on that particular section.

My driving partner, Whanganui journo John Maslin, and I also noted that cruise was no good at all once the torque-converter lock-up was breached on a hill, for instance, as the system would then kick down automatically and try to keep pace uphill, engaging a ratio or two lower than the lazy top-gear cruise we and the car had previously been enjoying. On steepish uphills, I found that driving the car out of cruise and deliberately keeping revs below 1600rpm was the best way to go, with the 3.6-litre engine's better torque delivery compared with the smaller 3.0-litre engined versions of the SIDI unit allowing smaller throttle openings without scrubbing off too much speed.

It's not without its stress, carefully monitoring the tachometer, the on-board computer's running fuel consumption readout and the average speed counter, as well as the road conditions and traffic around us. That's why a crew of two is so important, with two sets of eyes and two reserves of common sense to note when the driver is getting tired during long stints at the wheel.

Because the on-board computer is constantly revising the consumption average as it adds the immediate levels of fuel use to the running total, the readout can be horrifying.

For instance, when parking-up at our Wellington hotel at the end of the first day's run, our consolidated fuel use meant that as we shut the SIDI engine down – that means Spark Ignition Direct Injection by the way – our range for the second day, based on the first day's running was 430 kilometres.

That's more than enough to make Christchurch from Picton.

However, after the slowcoach trickle of traffic through Wellington to the ferry and then repeating similar driving conditions on the other side of Cook Strait, I noted that our projected range had dropped to exactly 100km.

Thus it was two worried, gulping, dry-throated SV6 pilots who drove out of Picton with, according to our computer sufficient gas for a third of the journey ahead of us.

Not to worry, once we'd cruise-controlled ourselves down as far as Cape Campbell, the more representative fuel use had our range recalculated to 380km. This meant that, all things being equal and with no more road works or stoppages, we should squeak into Blackwell's Holden forecourt with a little left in the tank.

However, with Wellington and the ferry playing silly devils with our average speed, we would have to cruise at a rather quicker pace than we would have liked, to reach the dealership without too much of a penalty.

But manage it we did, having averaged 77.71kmh and using gas at the rate of 7.91 litres per 100km.

Compared with our four other driver pairings, John and I were the second-placed of three 3.6-litre SIDI Holdens in the challenge in terms of fuel use (the better car did 7.77L/100km while the third ran out of fuel 17km north of Christchurch).

The smaller-engined 3.0-litre SIDI cars could probably have made it as far as Ashburton, as they recorded 7.36 and 7.26L/100km, with the astonishing latter figure being achieved by our own Paul Owen, a seasoned economy-drive contestant who uncannily managed to use the least fuel while maintaining the highest Auckland-to-Christchurch average speed of 79.94kmh.

Suffice to say, any careful driver should be able to get from our largest city to our best one on a tank of gas in one of these Holdens. Who knows, they may have a bet on it, like me. I'm now one chocolate fish better off.

- © Fairfax NZ News