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.

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Perhaps I am unusual in that as a guy in his mid-forties, I’ve owned relatively few carburetted cars. My first two cars were carby, but after that my main cars have always had electronic injection. And so I’ve got completely used to thinking in terms of cars with plenty of electronics controlling the fuel and ignition.

So it’s a real shock when I start thinking through modifications for my newly-acquired Peugeot 405 SRDT diesel. Clearly, being a diesel, you don’t expect to see spark plugs and an ignition coil and coil module and stuff like that. But the absence of a crank-angle sensor, MAP sensor or airflow meter, intake air temperature sensor and ECU comes as a bit of a shock. (The Pug injection is the old mechanical Bosch system, rather than today’s electronically controlled common rail system, that in many ways resembles a conventional petrol injection system.)

The shock isn’t so much in making changes to the fuel system; it’s in all the other avenues which are no longer viable. For example, the Independent Electronic Boost Control kit worked extremely well when I developed it. But I can’t use it on the Pug because there’s no electronically varying injector pulse width!  The Intelligent Turbo Timer  is another project that immediately springs to mind – but again I can’t use it because there’s no electronic indication of load.

And I’m finding that I really need to change completely how I think. A week or so after buying the car I was finding it harder and harder to get it started. The engine would crank many times before it sprang into action – to then, paradoxically, idle and run perfectly. What could be the problem? The cranking speed sounded a bit low so I put a multimeter across the battery – it showed just 7 volts on cranking! Hmm, I immediately thought, I bet the ECU can’t compensate in its injector pulse width when the voltage is so low – and the spark’ll be weak too! Except, there’s no spark and no ECU! Instead, the low cranking speed results in less compression pressure, and so temp build-up, and so ignited fuel. (I put in a new battery and the problem was immediately solved.)

None of these ideas is earth-shattering. But it’s interesting how I need to so dramatically change my mind-set – I guess, just the same as if I went back to modifying a carby car….

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It’s amazing how ‘normal’ is such a flexible term. That idea can be applied as broadly as you wish – normality in society simply depends on majority behaviour, nothing else – but here I’m applying it to fuel consumption.

The main reason I picked a Peugeot 405 diesel as our project car is fuel consumption. Like the hybrid petrol/electric NHW10 Prius that I turbo’d, the Pug has to maintain good fuel economy, even with the performance modifications that I’m doing.

Basically, if it starts to drink like a Commodore, the project’s a failure. [Where oh where is the Commodore diesel?!]

And I am not talking about fuel consumption in some economy run; nope, I’m talking my real-life consumption. Most of my driving is up and down the steep mountain where I live, plus a little urban and a fair serving of freeway.  Over long experience I have realised that this driving regime penalises small engine cars – they have to work really hard climbing the big hill – and so no economical car gets optimal fuel consumption in these conditions. That’s especially the case with the air con running. But that’s where my cars are driven, so it’s the fuel consumption that applies to me.

My hybrid Honda Insight, capable in the right freeway conditions of turning in a real-life 2.8 litres/100km, gets in the high Threes / Low Fours in my normal use. The turbo Prius, off the road now with a defective high voltage battery, got in the mid-Sixes.

Frank the now departed modified EF Falcon, got in the mid-Tens to low-Elevens and my standard Lexus LS400 (also now departed) got similar consumption.

And the Peugeot? The first tank, with the car driven on my local roads, yielded a measured economy of 6.9 litres/100km.

A 700-odd kilometre country drive, two adults, one child and a fair amount of luggage resulted in 5.7 litres/100km.

Another tank involved lots of performance testing, dyno runs, draining of fuel from the filter to remove water, and up and down the hill and some freeway work. The result was 7.0 litres/100km.

Now these results are pretty damn’ good. The Pug, while certainly no performance demon, is a comfortable car with room for four, a big boot, very good air conditioning (in fact, with the heavily tinted windows, amongst the best air conditioning systems of any car I’ve ever driven!), and – most critically – it cost only AUD$6900 to buy. (Even the cheapest hybrid is roughly twice the dollars.)

But today when I punched the calculator’s buttons to work out the consumption of the most recent tank, I was rather disappointed. After a whole bunch of mods (which we’ll detail in due course in AutoSpeed), mods which have revolutionised on-road performance, I saw the fuel consumption number and felt a bit miserable.

Yes, the tank might have included towing a 6×4 trailer loaded with two large bookcases – the aero drag on the freeway was like a giant hand pulling the Peugeot back! 

Yes, it also included the climb up the hill with the trailer, air con running and two adults and a child in the car; the 1.9 litre Pug was certainly working hard. (I’d love to know how hot the intercooler got!) And the air con was running for basically the whole time this tank of fuel was being consumed.

So 6.6 litres/100km is actually quite fantastic: but when I saw the digital numbers, I was disappointed. That’s what looking at the Honda Insight’s fuel economy read-out does to you… it changes your definition of ‘normal’!

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