Based on dyno tests and the hill-climbing performance of my diesel Peugeot 405, I decided an at-the-flywheel figure of 35 kW/tonne was about the right minimum.

I applied that idea to electric cars, where for reasons of lightness, battery power consumption and cost, an electric motor that errs on the side of smallness makes sense.

A number of comments were then made that this was completely wrong, that electric motors don’t work in that way (apparently, an electric kilowatt is different to a petrol motor kilowatt!) and so on. However, I saw no evidence that suggested a power/weight ratio of about 35kW a tonne was not the minimum for a car to be competent on the open road. (And a reasonably aerodynamically slippery car, at that.)

Recently, I’ve driven three cars that have a instantaneous power output display on the dashboard. These are all Lexus hybrids – the LS600hL, the GS450h and the RX400h. The latter’s display is shown above.

With this gauge I was able to see exactly how much power was being transmitted to the wheels, irrespective of torque curves, throttle position or anything else.

The actual power going to the wheels.

The RX400h weighs-in at 2040kg – say with my body mass, 2130kg.

Typically, I used in normal driving – even sporty urban driving – an indicated 50kW or less. That’s just a little under 24kW/tonne.

Getting into it more strongly, 75kW showed on the dial – but I stress, this was now going harder than most people would drive most of the time. That’s a power/weight ratio of 35kW/tonne.

To get 100kW (or higher) showing on the gauge, you had to be clearly pushing the car hard.

And 200kW? Full throttle and with lots of revs – completely unlike 99 per cent of daily driving.

I already know from the Peugeot that, if the car is being driven well, 35 kW/tonne is enough for open road driving – and now I know that it’s also sufficient for even quite sporty urban driving.

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.

So a new commercially-produced intake to an airbox might cost $600 – he wanted at least 6kW from it. An exhaust might cost $1000 – so at minimum, a 10kW gain. And ditto with the chip.

In fact, for many people, that cost/benefit ratio is still pretty much on the money.

Time passed, and by 2002 Paul was into Porsches. On his Porsche 993, that ratio jumped to $200/kW for modifications like exhaust, turbos, engine management re-mapping and an oil cooler. (Well, the last couldn’t be quantified in $/kW, but you get the idea.)

By 2007 the car had changed to a Porsche 996 turbo and the ratio for an exhaust and management re-map had dropped to $180/kW – and for a remap alone, just $66/kW.

Another, different, way I’ve seen of defining a cost/benefit analysis is to suggest that if a power improvement is less than 10 per cent, the driver won’t be happy.

Why? Because they won’t be able to feel the change in performance.

This idea was suggested to me by a manufacturer of extractors and exhausts: if in dyno testing, they couldn’t get a 10 per cent power improvement, they didn’t sell the product. Why? Because they knew that irrespective of the cost to the customer, the customer would be back with complaints.

Of course, quantifying performance improvements in terms of peak power figures alone is flawed – what about part throttle response, bottom-end torque (and so driveability), fuel economy and so on?

Take into account these factors and the cost/benefit becomes very personal. If you are doing the modifications yourself, the ‘cost’ part of the modification may also heavily involve individual effort.

I have been thinking of these ideas after publication of three stories in AutoSpeed, all of which are based on modifications I have made to my Honda Insight.

In order of publication, they are The 5 cent Modification, Tweaking the EGR Part 1 and Part 2, and Trialling a Rear Undertray.

The 5 Cent Modification used a resistor to alter the output signal of the intake air temp sensor. It was a modification that was incredibly cheap and very simple to fit, with minimal testing needing to be undertaken.

Any benefit at all from this modification and I’d have been happy – but with the much improved driveability, the modification is probably worth $500 to me. $500 versus 5 cents, and with only a few hours needing to be spent, is a pretty good cost/benefit ratio!

But Tweaking the EGR was a much more borderline modification. This modification changes the amount of exhaust gas recirculation that occurs at part-throttle. Again it was cheap and pretty easy modification to install, but setting it up and then proving its worth took a lot of testing.

I think it’s a good modification – especially as it improved the fuel economy on a car with already exceptional fuel economy – but personally, it’s worth to me perhaps only $200. But again, that’s still a pretty positive result.

The undertray, though, was a different story. The first step was to tape into place a plastic trial undertray and then do some testing. Installing the trial undertray took about three hours; testing it took literally hundreds of kilometres of continuous freeway driving.

When I previously did an undertray on a Toyota Prius, the improvement was noticeable pretty well straightaway. With the Honda, I couldn’t detect any change at all, either in fuel economy or car feel.

As has been suggested to me, I could have then trialled a differently shaped undertray; I could have changed the way the leading edge was organised; I could have used vortex generators on it; I could have made different wheel fairings.

But instead I chose to take it off!

The undertray was a good example of where for me, the cost - especially in time being spent - heavily outweighed the benefit. To be worthwhile continuing, the trial undertray should have made a clear change to the way the car performed – whether that was to make things worse or better.

No change at all and I couldn’t see any point in persisting…

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.

The other day I could put this to the test. I wasn’t standing alongside an empty road, but instead close to the track where Human Powered Vehicles were racing. The event was the Holden Maryborough Technology Challenge (see here for the account I wrote of last year’s event) and the variety of vehicles was large. (Incidentally, I commend Holden for their on-going sponsorship of this event.)

The human-powered vehicles varied greatly in their aero slipperiness. Worst were the conventional recumbent trikes, about as aero slippery as bricks! Best were the fully-faired vehicles – extremely slippery not just in comparison to their unfaired competitors but also in absolute terms.

Half way along the main straight, and on pedal power alone, the best vehicles were achieving speeds of 40 km/h. (And incidentally, doing this for a full 24 hours of the race – it’s a stunning event.) By standing close to a barrier, I could be within a metre of them as they whizzed past.

Vehicles like the one pictured below clearly disturbed the air; the vehicle would shoot by, there’d be a pause, and then you could feel the turbulence.

But when this machine rocketed past (pictured is the winner), there was a pause – then nothing!

It was downright eerie, waiting for the air motion and then experiencing nothing that was discernible. Even stranger was the expectancy that, with the vehicle’s higher speed, you’d feel more buffeting – not less.

Perhaps it’s worth standing by the side of the road and assessing the wakes of different cars? I think I might just do that…

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.

I think a few words about the car – which I called “The Railton” in his honour – will interest you because it is a most unusual design. It is, for instance, interesting that my 3-ton car was half the weight of Eyston’s “Thunderbolt” and had only half the power.

Railton had to start planning the car on two things – the tyres which were available for the job, and the somewhat old-fashioned Napier Lion aero engines which were all I could get, and both these things meant that the weight of the car had to be as low as possible to get the speeds we were after. Such speeds were obtained by perfect stream-lining.

First of all, the car has no chassis frame like ordinary cars. Instead, there is a single backbone girder down the middle. This is “kinked” in the middle so that the two engines can be slung alongside the girder, one each side and back to back, running in opposite directions. This arrangement balances out the twisting action of an engine when it is working and makes the car very steady to drive.

Next, one engine drives the back wheels and the other drives the front wheels, and this four-wheel drive makes it possible to use full power for gaining speed without the danger of the wheels merely spinning round and slipping on the ground. The engines are supercharged at a fairly low pressure and each one gives 1,400 h.p.

I had two three-speed gearboxes with a very high top gear, and I could do about 250 m.p.h. in middle gear!

The body is a very special streamlined design, made after a long series of careful scientific tests with models in a wind tunnel. It is very light and it fits down over the whole car, with a very long, streamlined tail. My driving seat is right out in the nose of the car, ahead of the front wheels, and my head is covered in a streamlined conning-tower.

From start to finish, it took three years to plan and build the car.

There is, so far as is known, only one place on earth where records at such high speeds can be done, and that is the dry bed of a salt lake in Utah, U.S.A. It is under water part of the year, but when it dries out in. the summer, the bed of the lake is made of smooth salt crust which is as nearly perfect for record runs as anything could be.

I first went there in 1938 when I got the record at 350 m.p.h. We altered a few things on the car after that, and in the following year I raised the speed to 369 m.p.h. But all the time I felt sure the car would reach the magic figure of 400 m.p.h. so, after the war, a few details were changed (one thing was a device for preventing the engines from stalling when I changed gear) and in 1947 I went over to Utah a third time.

As you may know, I got the record at 394 m.p.h., average of two runs, and my fastest run in one direction was 403.14 m.p.h. If the salt had been in better condition, for it was beginning to break up and on one stretch was very bumpy, I am convinced that the average for the two runs could have been over 400 m.p.h.

I have often been asked what that enormous speed feels like, and that is very difficult to put down in words because the sensation is quite out of this world. There is not a lot of room across the lake bed. Given more room to get going, and a longer distance in which to slow down again, the car would go even faster, because it was gaining speed right through the measured mile.

I had only six miles to gain speed and this means that I had to use all the power of the car the moment it started off from rest. I cannot describe the feeling of the enormous power except to say that it made any racing car seem like a toy and it was as if a colossal giant was hurling me forward.

At each mile there was a big sign board with the number of miles left to go painted on it. Down the centre of the fairway which had been swept clear of loose salt there was a big black line, and I sat the car across this, astride, as it were. I focused my eyes about a quarter of a mile ahead. The instant I spotted the mile-post next ahead, it shot towards me and vanished, so fast was my speed, so that I only got a glimpse of each board in turn, and the miles in between flashed past like a hundred yards instead of 1,760 of them. Each mile was taking about 10 seconds!

The car was amazingly steady, thanks to the four-wheel drive design and the counter-balanced engines. I changed up into middle gear at about 120 m.p.h. then, a few seconds later, at 250 m.p.h., I snicked into top gear, and then the engines really took hold and hurled me along faster and faster.

The black line unreeled under the wheels, the mile posts flicked at me and were gone, I had a vague impression of a misty horizon in the distance and down each side of the 40-foot swept track it was rather like a thick fog, for I could see nothing at all. I had to steer the car constantly, just like keeping a touring car straight, because I dare not lose that unwinding black line which alone kept me going in a straight line.

Suddenly the start of the measured mile flashed up and was gone after my six miles run-in, and now the car really was going. The roar of the, engines just behind my head rose to a deafening thunder (although I wore ear-plugs), and the entire machine vibrated as it shot over some rough surface, whilst the wind rushing past with the force of a hurricane rose to a deafening screech round my conning-tower. By the time you could count nine the end of the measured mile flashed up and was gone, just as the instruments registered 410 m.p.h. and I took my foot off the throttle.

Instantly everything went silent. The wind scream died away gradually, the vibration ceased, but I felt as if the car would never even begin to slow down. Mile after mile flicked past and then, when I saw I was down to 300 m.p.h. I jabbed the brake pedal, but it was like jabbing cotton wool—nothing happened at all so far as I could see. Actually, the powerful, water-cooled brakes had slowed me. I jabbed again and again, letting the brakes off in between because the shoes were more than red hot and the cooling water was flashing into steam. Gradually, gradually, I lost pace … 250… 200…and well into the last mile, the speed really fell away. I put the brakes hard on and the car rolled silently to a standstill.

That was the first run. Then the car was turned round, the tyres were changed, other details were seen to and then off I went again, back the way I had come.

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.

This book assumed all my knowledge and then took it far, far forward.

I permanently ‘borrowed’ it right up to the time I left school…

And then, just the other day, something similar happened. This time the topic wasn’t solar energy but car aerodynamics.

Car aero is a topic I’ve been teaching myself about for close to 20 years. Over that time I have built up a very good reference library on the topic – nine or ten books and as many engineering papers. (That doesn’t sound like much but there are simply not many books available.)

The best of those books is Aerodynamics of Road Vehicles, edited by W.H. Hucho. It was first published in 1987 but remains the ‘bible’ on the subject. Another really good book is Race Car Aerodynamics – Designing for Speed by J. Katz. This book was first published in 1995.

However, like many other aero references, Race Car Aerodynamics is – as its name suggests – is all about downforce and racing, rather than the aero of road cars. And the more you go into road car aero, the more you realise that conventional racing provides little relevant information…

Rather like solar energy a long time ago, I figured I had all the good gear on aero. I certainly don’t think that my knowledge of the subject is much more than infinitesimal, but by the same token, I didn’t think that there were many books around that I could use to extend my knowledge. (The more complex ones I simply can’t understand.)

And then it was suggested to me that I might want to read a book. Called The Leading Edge, it is subtitled Aerodynamic Design of Ultra-Streamlined Land Vehicles. It’s basically about the aero design of solar race cars; it was first published in 1999. The author is Goro Tamai.

I’d seen the book advertised but assumed it would be rather like the Katz book – good but not really relevant to road cars.

But then I borrowed The Leading Edge.

Ohmygod!

Talk about brilliant! Yes, The Leading Edge is primarily about solar racing cars. But in a way I don’t think the author really envisaged, it’s also shows the criteria that (some) cars of the near future will need to satisfy.

You see, to achieve an aero drag that’s a great deal better than current cars, the engineering aims need to change. No longer is pressure drag (ie the size of the wake) the critical factor, but instead skin friction and boundary layer effects become vital. ‘Wetted Area’ becomes damn-near as important as ‘Frontal Area’; cars slide through the air rather than punching holes in it.

By describing in detail the techniques required to achieve drag coefficients of way under half current cars, the author shows what characteristics those new cars will need to have. But it’s not all theory: the book also covers in excellent detail on-road (as well as wind tunnel) testing and development.

If you’re interested in car aero, The Leading Edge is not the right book to start with – instead read (or borrow) Hucho’s Aerodynamics of Road Vehicles. But if you want to go the next step in seeing where road car aero is heading, The Leading Edge is brilliant.

And if you’re building your own machine – whether that’s a Human Powered Vehicle, a one-off car, or a kit car – The Leading Edge is absolutely compulsory reading.

Footnote: if you read The Leading Edge make sure that you first download the corrections and updates here.

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.

Performance nuts always talk acceleration times, but acceleration is enormously power-hungry. So what, in the real world, is sufficient power?

One answer is the power required to drive along a country road at the speed limit. In addition to the power required to overcome aero drag, you also require the additional power to climb hills.

Thinking along these lines as I drove open road kilometre after kilometre, I realised that the 1.9 litre diesel in the Peugeot was probably very close to the requirement. Oh no, not its peak power output, but instead the full-throttle power it was developing at about 2000 – 2500 rpm.

The Peugeot runs these revs in fifth gear at around the open road speed limit, and I found in the 1100-odd kg car that nearly every open-road hill could be climbed without a down-change (and so using higher revs). There was also enough power to battle headwinds, overtake slower cars, etc. No, you’re right – holding it in fifth and just flooring it didn’t make the Pug a performance car (not by a helluva long way!) but it was just competent.

And having dyno’d the Peugeot, I can tell you exactly how much power is available at the wheels at 2000 – 2500 rpm. The answer is about 30kW.

Now it starts getting tricky, but in round figures, I therefore reckon an at-the-wheels power/weight ratio of about 27 kW/tonne would be sufficient, if the powertrain was geared so that maximum electric motor speed was reached at the open-road speed limit.

Running an electric motor developing an at-the-wheels 27 kW/tonne and gearing it so that peak electric motor rpm occurred at 110 km/h in top gear would therefore give sufficient open-road performance. And, with the ability to then lower the other gear ratios, torque multiplication would be increased at all lower speeds.

This is not some profound breakthrough, but it does show two things.

If you’re prepared to live with a maximum speed of 110 km/h, and you have an aerodynamically slippery car, an at-the-flywheel power of (say) 35kW/tonne is probably enough for the real world.

And when you’re working with such low power outputs, and a motor that’s most efficient at its rated (high) speed, gearing is very important.

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.

The primary trouble with the VL – it was the first car I ever wool-tuft tested on the street, still and video cameras in action – was its rear end. The boot was too low, and the rear window angle too steep, to give attached flow to the end of the car. Instead, the airflow separated at the end of the roof and the rear window and boot lid were a mass of turbulence. (Of course, that’s why the Walky had the raised boot lid.)

So where could I go for help? Nowhere – until I discovered a tech paper on the development of the Peugeot ‘VERA’. It’s now so long ago that the tech paper – that I still have – has lost its cover page, so I don’t know if it was published by the SAE or some other organisation. But I do remember my absolute joy in finding it and applying its ideas to the Commodore.

You see, the thing that made it relevant is that VERA was a developmental vehicle that tried to optimise a Peugeot 305 three-box sedan for aerodynamics, all by using just add-ons. In other words, it was a car where the fundamental glass-house and panels were not to be changed.  And VERA was stunningly successful, with the measured drag co-efficient dropping from the standard car’s 0.44 to just 0.31. Front-end lift was also reduced – in fact, front down-force was created.

The paper details different front and rear spoilers, wheel fairings, deletion of glass mouldings, changes in engine bay cooling drag, side window deflectors, sealing of front-end gaps, venting of front wheel arches – and a whole lot of other stuff, most of which could also be applied to my Commodore which had a very similar rear window angle and effective boot-lid height. 

At the time, it was a lot of fun playing around with the ideas that the engineering paper gave me.

I’d forgotten most of this until I bought my Peugeot 405. One day I was looking at the car in profile and I suddenly realised it reminded me of that old VERA-version 305. I dug out the tech paper and it’s clearly obvious that Peugeot used some of the aero lessons from that development car in the later model. And while I had the paper in hand, I read it through again – and it’s really very good (in fact, perhaps the best ever published) on improving the aerodynamics of a ‘traditionally’ shaped car.

So if you have an older car, keep in mind that there’s a major resource available in the shape of the engineering papers written when your car was current.

PS: I couldn’t resist doing a web search to see if I could find a pic of VERA – and here it is. And when I saw the pic I spotted something else I’d not since realised – the front wheel arch venting looks very similar to the approach taken on my Honda Insight (one of the world’s slipperiest cars)… so maybe plenty of others also read that seminal paper.

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.

The CO2-powered drag racers also looked fascinating; however time constraints meant I could only see a few runs made. But hell, they were fast!

But it was the human-powered vehicle race I got the most kick out of. Constructed by the schools involved (although, some schools had done all the construction themselves and others had farmed things out to external tradespeople – a bit of a cop-out), these vehicles consisted almost entirely of recumbent trikes. Some were running full aero-reducing fairings but most were bare. Construction quality and design varied from abysmal to fantastic.

The course, a street circuit with an added hairpin, was largely an endurance layout rather than having challenging corners.  And endurance was certainly needed – for this was a 24 hour race. The school teams, complete with pit area tents and full support teams, ran a roster of riders but each machine had to go the full 24 hours. I watched them head off at 1pm, the students fired with enthusiasm and riding like their lives depended on it. Each time their entrant came past the pits a cheer erupted from the watching team members.

By dusk the pace had slowed a little, but the teams were still cheering, lap after lap. The headlights and tail-lights were on by now, and the first signs of mechanical failings were starting to occur. A chain not meshing smoothly, a drink bottle hose trailing behind a red-faced rider, one machine without its headlight working.

I went back to my motel, had a few drinks, checked the current race standings on-line, then went to bed. But as I went off to sleep, I thought of those riders still pedalling, those trike frames creaking and groaning each pass over the bumpy rail line, the young people finding the mental grit and determination and concentration to keep on racing, following the right cornering lines, keeping out of the way of the faster traffic, talking by two-way to the pits, monitoring their lap times – and doing it all with their thighs and calves on fire…

At 9 o’clock the next morning I was back, having had a good sleep and a relaxing morning coffee. And there they still were, those racing machines, pushing their way around the track, the local SES emergency volunteers looking sleepy and bored, the dwindled spectators subdued and red-eyed.

And some of the machines were still going fast, stopping the big-screen radar display at 30 and 31 km/h. The front-wheel camber on a handful of machines had grown mightily overnight; some had developed a sinuous steering motion that would have been effective if it hadn’t been occurring on the straights; there were rattles and odd noises galore – and yet there were machines that still looked as tight and strong and sturdy and sweet as the hour their construction had been finished…

And there were crashes – I saw one very tired rider make the mistake of pulling on the right-hand brake caliper instead of the left and steer straight into a barrier – and the teams were talking about a roll-over. The steering on one machine went into radical shimmer as the tie rod fell off and some machines literally rattled their way around the whole course.

I wasn’t there for the finish but the top six machines didn’t change much over the last 12 hours of the race.

I thought the weekend event quite fabulous – it’s great seeing people so focussed and committed, pitting themselves in most cases against the merciless clock, with real challenges involving physical and mental effort. 

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.   It’s an intriguing idea. So, being as I say too sick to work, today I went off to my local Japanese importing wrecker. But: “No mate, nothing like that here – and we wouldn’t get something like that small in anyway.” Hmmm. Then I took myself off to a really big wrecker, one that sources just locally crashed cars. The prices are high, but the access to the full yard of crashed cars is priceless. There I wandered at will, looking at the cars and thinking of weird hybrid three wheelers.  

And the best bet was, I thought, a Daewoo Matiz. The Matiz, which we tested here, certainly doesn’t look like a good starting point. Not with just 37.5kW from its 3 cylinder 800cc engine. But then again, this four door car weighs 780kg, giving a standard power weight ratio of 44 kW/tonne. Still pretty awful – but what if the car lost 200kg of bodywork and wheel? Then the power weight ratio would be 65kW/tonne. And what then if it got a little turbo – a neat 100 kW/tonne would be pretty easy. 130-odd horsepower per ton isn’t something radical, but it would be fun. 

The Daewoo has a major advantage over other cars – it is built as a low mass car. The suspension is small and light, for example. It’s not a downsized big car but a small car to start with. The suspension from (say) a Toyota Yaris is huge in comparison. The other advantage for us here in Australia is that it was sold locally, so all parts are available. (The Japanese 660cc turbo FWDs were never sold here.)  

And what form would such a car take? Well, I don’t think it would need a windscreen – just wear helmets. The driver’s side could be made spacious and roomy at the expense of a rarely-squeezed-in passenger. If you don’t have a windscreen you don’t legally need a demister, so (in the wonderful climate in which I live) you could get rid of the complete heater/demister unit. In fact, get ride of the whole dash, retaining just the instrument pod and switchgear. Put the fuel tank behind the seats and ahead of the single rear trailing arm suspension. I assume that as a motorbike/trike, the front and rear brakes could be separated in function, so have the foot pedal work only the front wheels and use a hand lever for the back wheel. Don’t have doors – just hop in over the high sills. The absence of doors makes legal registration easier (no need to prove door-bursting strength) and with the depth of the sills, the tubular frame structure could be made very strong but still light.  

In fact, really the only thing that would prevent the design being aero efficient, fun and fast would be the bodywork. To get low drag you’d need a pretty trick body – especially without a windscreen. (You’d need full fairings behind the heads, etc.) And the required compound curves would need complex and expensive moulds – even if done in fibreglass. The work of a really good industrial designer or car stylist would also be a necessity. (You could instead go for a minimalistic bodywork design, but then with the available power, the performance wouldn’t really cut the mustard.) 

Hmmm, now what I need to find is a Matiz that’s had a rear-end collision and is for sale for about five hundred bucks, a brilliant beginner car stylist and a fibreglass expert…

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.

I immediately emailed the company.

From: Julian Edgar

To: info@fuelsavers.com.au

Sent: Thursday, April 27, 2006 7:03 AM

Subject: media test request

I note your website at http://www.fuelsavers.com.au/ and the vortex generating fuel savers.

I’d like to do a test on the product for www.autospeed.com, the world’s largest fast car website. We produce a daily article for our readers and have been doing so for nearly 7 years.

I’d considered developing vortex generators as a modification story but clearly if the off the shelf ones work well then this would be an easier way of readers achieving the outcome.

The aerodynamic undertray stories we did (see Modifying Under-Car Airflow, Part 1 and Modifying Under-Car Airflow, Part 2) attracted considerable reader interest.

We would test the vortex generators on a NHW10 Toyota Prius sedan, for which I have detailed constant speed fuel economy test results.

Julian Edgar, B.Ed, Dip T (Sec), Grad Dip Journ, AFSAE

An email duly came back from Mike Chadwick, one of the contacts listed on the website. He said he’d be happy to send AutoSpeed some for some independent testing. He also asked for my phone number as he wished to chat. I sent the number and a day or so later he phoned.

It eventuated that Mr Chadwick is an aircraft maintenance engineer and had spent some time developing the vortex generators. He’d tried them on his son’s car, a Vectra hatch, and had video of this car wool-tufted, with and without the vortex generators. Some trucking companies were also using them, he said. I requested a copy of the video footage, the contact names and details of the trucking companies he said were getting good fuel consumption gains. I also pointed out that the reduction in aero drag would need to be very great to achieve the fuel savings of “up to 11 per cent” being claimed on the website. (Well, they would if the fuel consumption savings were going to be anywhere near 11 per cent!)

I also made the point that when we test goods, we will publish what we find, whether that’s good or bad. In the phone call I expressed a little scepticism as to whether the vortex generators would work well on hatches with vertical tails (the website shows pics of a Hyundai Getz equipped with the devices) but Mr Chadwick blithely dismissed these concerns.

I got the feeling that Mr Chadwick had not talked with anyone who expressed scepticism based on a knowledge of car aerodynamics (as opposed to just a scepticism about any fuel saving gadgets!) but near the end of the call he casually mentioned that he thought we’d find them as interesting as General Motors Holden, who were (apparently) happily testing them. He also said he had patented the concept.

After the call I emailed, requesting the patent number(s) – a patent has to reveal nearly all the details of the device, so that would be good background.

Back came Mr Chadwick’s email, but this time with the tone rather markedly changed. Could we supply details of the tests we would conduct, he asked. When were we going to conduct the tests because Fuelsavers would be interested in viewing the test and assessing the results, he wrote. He also supplied a patent number but not the country in which it was issued. (A search reveals it’s an Australian patent.)

After the debacle of testing the Davies Craig Electric Water Pump, something we spend a great deal of effort doing (see Testing the Davies Craig Electric Water Pump – Part 1) , I like to make things as crystal clear (although I thought I already had)…

Mike,

As a matter of editorial policy we do not show articles to those supplying goods for review.

The test would involve fitting the devices to an NHW10 Toyota Prius and comparing fuel consumption with that already being achieved in a variety of conditions. It may also involve comparative wool-tuft and/or surface pressure testing.

If you have any problems whatsoever with any of the above, I urge that you reconsider the supply of the goods.

In what country is the patent issued?

Julian Edgar

And I never heard from Mike again….

Footnote: I have since found another source of vortex generators – so stay tuned for more on this topic!