Victor Harman offers some advice for eking out that bit more from your refuel.
Never mind the extra mile. The 2011 MPG Marathon event this month could be a tight enough finish that even a few hundred yards will make a difference! 40-odd teams of two driver cars will be setting out to cover around 400 miles in two days, from a base at the Cotswold Water Park, south of Cirencester, and Diesel Car contributors are strongly represented this year. Editor Ian Robertson, Sue Baker, John Kendall, Peter Cracknell, Andrew Andersz and I are respectively driving the new Peugeot 3008 HYbrid4, a Skoda Octavia GreenLine II, a Citroën Nemo Van HDi 75, a Suzuki Swift 1.3 DDiS, a Kia Rio 1.1 CRDi ecoDynamics and a Citroën C4 1.6 HDi. There’ll be plenty of competition within the Diesel Car team and word has already escaped of friendly wagers! We’ll be driving for the honour of Diesel Car, and have plenty to live up to in terms of past performances, with John Kendall’s winning record in the light commercial class almost as boringly predictable as golf tournaments were before Tiger Woods lost his touch.
Shell Fuelsave have replaced Total as co-sponsors of the event, along with ALD Automotive, the AA, TomTom, the Energy Saving Trust and Fleet World magazine. Competitors will thus all be running on this new standard price Shell Fuelsave Regular Diesel which, in Shell’s words, “is enriched with Shell Efficiency Improver, designed to improve fuel economy from the very first drop.” We’ll need every drop of that additive over those two days. As a competitor, what do I think will be the keys to a winning performance? I’ve written previously in some depth regarding the base principles of economy driving; mental attitude, planning, anticipation, and speed control. All these will be critical, but I feel that the motorway and dual-carriageway sections will possibly win or lose an award. The entry cars are very clearly marked with large body signage and this is one time when one has to be totally focused. Other drivers will see exactly why we are driving slowly and speed will be the key. High speeds gobble up fuel and it will be best to go into these stretches, totalling around 100 miles, with time in hand and the firm intention of cruising as slowly as possible, in the most appropriate gear, to maintain the 32mph average set for the event. So planning to arrive at the end of each day as comfortably close to the day’s time limit will be important. Over 200 miles the difference between averaging 32mph and 33mph is around 12 minutes. Even assuming that only half of the fuel is used in overcoming aerodynamic drag, arriving 12 minutes early at the finish each day could mean using as much as three per cent more fuel – and that difference of around 2.5mpg could easily win or lose an overall or class placing.
Some of you may be thinking about the idea of ‘coasting’ in neutral. In reality, I think there’s little opportunity for saving fuel this way and current technology make the potential gains even less. Modern fuel injection cars shut off the fuel supply completely on the overrun with a closed throttle, when the car’s momentum is driving the engine. Only if the engine speed drops below the normal slow running setting is the fuel supply restored to keep it running. So selecting neutral and coasting will often use more fuel. Shutting the engine down is, of course, highly dangerous, as power steering assistance is lost and there are other safety considerations with no engine power. So coasting is really out as an economy wheeze, as similarly is slip-streaming other vehicles, which is strictly forbidden. We’ll be publishing the event results in the next issue and reporting on the adventures of our five competing teams, who hopefully will be bringing home some silver for the Diesel Car display cabinet.