When modifying cars, everyone conducts some sort of cost/benefit analysis.

That might be as informal as weighing-up the likely cost of the modification against the guessed benefit, or it might be a more detailed analysis.

A friend of mine, Paul, has a rule of thumb that goes like this:

Back in 1998, on naturally aspirated cars, he budgeted $100 per kilowatt for a power improvement. Any more than that and he thought the value poor; any better than that and – well, he thought that was pretty good.

That $/kW ratio was for mods like intake, exhaust and chip.

• » Continue reading or Comments (11)

As we covered in Analysing Road Car Drag, most aerodynamic drag of current vehicles is created by separation pressure drag. Put simply, this is reflected in the size of the wake – the cross-sectional area of the disturbed air dragged along behind the car.

The most slippery vehicles in the world – the solar race cars – have reduced separation pressure drag to the extent that the other types of drag (eg viscous drag, induced drag and interference drag) become more important.

But in all conventional cars, it’s separation drag that remains the big one.

Now this gives rise to a rather interesting idea. Imagine you’re standing alongside an empty road. The day is a still one – there’s not much wind blowing. A car is rocketing towards you along the road, travelling at perhaps 100 km/h. It will pass close by to you. It grows in size and then roars past.

Now – what do you feel?

Clearly, you will be able to feel the wake – the eddies and turbulent air indicative of the aerodynamic disturbance of the car. This disturbance will take into account the separation pressure drag and the frontal area of the car – the two when multiplied form the vast majority of the actual aero drag that’s experienced by the car.

And, equally clearly, the smaller the air disturbance that you can feel, the greater the slipperiness of the vehicle.

• » Continue reading or Comments (3)

I recently bought a book published in 1950. Called Speed – the Book of Racing and Records, it covers fast machines on both land and water.

Written at a time when the United Kingdom held most of the records, it’s a brilliant read as the contributors are often the men who held the records. One of the best chapters is by John Cobb, then the holder of the world Land Speed Record.

Here it is.

The idea of building a new kind of car to attack the World’s Land Speed Record, which is the out-and-out fastest that any car of any size has ever travelled on the earth, came when I was driving my big 500h.p. Napier-Railton at Brooklands Track.

This very large car had been constructed for me to designs by my friend Reid Railton, an engineer whose talents, in my opinion, amount to sheer genius. The car was born on a drawing board and although I was perhaps a little dubious about its possible performance, everything that Railton said it would do it did – and rather more. It was admiration for his brains that led me to think that if ever a man could design a car to beat the World’s Record, then held at 300 m.p.h. by Sir Malcolm Campbell’s “Blue Bird”, that man was Reid Railton.

As things turned out, the car he designed for me did exactly as he said; in fact, his theoretical prophecies were rather on the pessimistic side and the car did better than he expected.

• » Continue reading or Comments (3)

It’s happened only a few times in my life, and each time it’s been a salutary experience.

One occasion I can remember is a long time ago. I was in junior secondary school and was heavily into solar energy. I’d constructed my own solar water heaters, solar pie warmers and other bits of gear. I knew about meridian altitude, I knew about flat plate collectors and thermal mass.

I’d also read all the books I could get my hands on that dealt with solar heating and knew inside-out the (handful) of books on the topic in the school library.

In fact I was pretty smug about my level of knowledge and understanding.

Then a new book came into the library. I can even remember its size and shape – it was a book long in landscape direction and had soft covers. It was also quite thick.

I remember I picked this book and started looking through it with little interest. After all, I already knew everything about solar energy…

But, all of a sudden, I went very quiet and became intent. I was just about to discover a whole new world of solar energy complexity and relevance; my learning on the subject was going to progress hugely.

• » Continue reading or Comments (6)

A while ago I attended an electric car show held in Sydney. I made the 2000-odd kilometre trip in my Peugeot 405 diesel, a car that, incidentally, gained high Fives (in litres/100km) for the trip.

At the show I briefly sampled three of the home-converted electric cars – a very interesting experience. And on the long drive home to the Gold Coast, I had plenty of time to reflect on these cars.

The electric cars I drove each retained the original gearbox: the electric motor was bolted up to the ‘box and the ratios could be selected by the driver. Typically, the cars were started off in second gear and then third and fourth and fifth gears were used as appropriate. (I used first gear off the line and felt an immediate gain in starting performance.)

But none of the cars I drove had performance that came close to conventional petrol engine (or even commercial hybrids). Even when the electric motor was rated at a higher power than the original engine, the massive weight of batteries substantially dulled the resulting power/weight ratio.

Putting in a more powerful electric motor (or running two electric motors) would of course help solve that, but at the expense of greater electrical power consumption that in turn would need either more batteries or result in a shorter range (and none of the ranges were very good to start with!). However, all the cars could easily exceed the 110 km/h open-road speed limit.

Clearly, what is needed is an electric motor that has only enough power to do the job – but no more.

• » Continue reading or Comments (35)

Over the years I’ve spent a lot of time in TAFE libraries (for those not living in Australia, technical college libraries). In addition to the very valuable automotive books, it’s the engineering papers that are the most interesting.

Each year the Society of Automotive Engineers publishes numerous technical papers on all topics automotive. You can buy them as downloadable pdfs by going to www.sae.org – but because you can see only a précis of the paper before you need to get out your credit card, this can be an expensive way of acquiring information. However, technical college libraries often have some of the papers, especially in the book form that the SAE occasionally publishes.

The ability to keep on the cutting edge of change is one clear advantage of the SAE engineering papers, but there’s another major advantage that’s often overlooked. And what’s this other advantage? If you own an older car, it’s possible by consulting the papers of that era to find stuff that’s directly relevant to your machine.

In 1990, when I owned a VL Holden Commodore Turbo, I was frustrated by its lack of aerodynamic development. The standard car was lousy and there were no simple off-the-shelf improvements available. The HDT Brock Commodores had body kits developed with no scientific input, and the pictured groundbreaking ‘Walkinshaw’ Group A, the first HSV model and one shaped with a huge amount of wind tunnel work, was too expensive to buy. (And it didn’t have the turbo engine.) And because the Walky was a near new car, you also couldn’t buy copies of its body kit.

• » Continue reading or Comments (1)

I spent last weekend at Maryborough in Queensland. So what was happening in this pretty town, a little inland from Fraser Island? The Holden-sponsored Maryborough Technology Challenge (MTC), that’s what!  

The MTC consists of technical competitions designed for school students, both primary and secondary. The challenges – that are really races – are fun and pedagogically worthy. Amongst other events, they consist of pushcart races, solar-powered boat races, robotics challenges, CO2-powered miniature drag racing and a human-powered vehicle race.

I went along primarily to watch the human-powered race but found myself much enjoying the solar-powered boats. The boats race side by side in pairs, pushing their way through a long shallow pool. They are kept in line by wire guides following two stretched longitudinal fishing lines.

The differences in boat performance were extraordinary – some boats just plugged along while others lifted their polystyrene noses and powered through the water, leaving a substantial wake. One student that I quizzed told me the electric motor driving his craft was Swiss-made – it was about as big as an AA cell yet gave the boat amazing performance. And of course, all the boats were directly powered by the solar cells mounted on them. As a way of integrating into the curriculum concepts of hydrodynamics, solar cell and motor efficiency, propeller pitch, renewable energy (and of course team-work and co-operation), I thought the boats were fantastic.

• » Continue reading or Comments (1)

As I write I’m getting over a cold. I am well enough to be mobile but not well enough to work. Well, that’s what I tell myself anyway.  

As many of you will know, I am becoming more and more interested in lightweight vehicles. One of my cars is a Honda Insight – amongst the lightest of all production cars on the road – and I find the downsides of its design usually quite minor. (If I need to carry more than two people, I take Frank the Falcon.)  

Now the Honda might be light, but it still has four wheels when surely three would be enough. Using a tadpole configuration (two front wheels and one rear) would also allow the car to be nicely streamlined, something that would be helped by a front mount engine and front wheel drive. That way, the classic teardrop shape for low aero drag would be much easier to implement.  

The starting point for such a car would be a FWD half-cut, say a Mira or Suzuki 660cc 3 cylinder turbo. Use the complete driveline, subframe, steering and front suspension and brakes, add on a tube frame chassis and then run the single rear wheel and suspension from a motorbike.  

• » Continue reading or Comments (6)

When the latest Evo model Mitsubishi Lancer came out I looked with interest at the rear fins stuck all over the trailing edge of the roof.

Mitsubishi calls them vortex generators, a term I was already familiar with from aircraft. Some aircraft use vortex generators placed on the upper surface of the wings to delay flow separation and so reduce the speed at which wing stall occurs. But the Mitsubishi isn’t an aircraft flying along, so what do they do on that car? A tech paper from Mitsubishi soon revealed that they improve the flow of air down the rear glass, so getting more air to the wing and probably also reducing the size of the wake.

I was inspired enough by the design to make a bunch of my own (using the alternative shape shown in the tech paper) and stick them over the trailing edge of the roof of my NHW10 Prius. However, on-road testing showed that the reduction in drag (for that was what I was after) wasn’t enough to make a dramatic difference to fuel economy, as I had already achieved with my frontal undertray.

So I put the idea to one side, perhaps for later revisiting with different shaped vortex generators or another car.

But when I came across a discussion group post that talked about an Australian company selling vortex generators with the aim of reducing fuel consumption, my interest was again aroused. The company, VG Fuelsavers, had recently featured on local TV as an invention worth watching. The website http://www.fuelsavers.com.au showed some pics of the vortex generators, which are made of sheet aluminium and look much more like aircraft designs than the shape of the ones used on the Evo Lancer. A kit of nine vortex generators with fitting instructions, cleaning wipes, double sided tape and a template cost AUD$110, including delivery. Which seems fine by me.

• » Continue reading or Comments (2)