While car modifiers talk endlessly about exhaust systems, there is surprisingly little hard information about the design of exhausts, especially mufflers.

That’s why I was particularly interested to come across the text that follows, contained in – of all things – a book on corrosion of cars, published exactly 50 years ago. The chapter, by H. Silman of Electro-Chemical Engineering, is a great summary of exhaust muffler design.

The automobile exhaust system consists essentially of three parts:

(1) the exhaust manifold, which collects the discharged gases from the exhaust ports and conveys them by means of a pipe at least one-quarter of the diameter of the cylinder to the silencer,

(2)  the silencer, and

(3)  the tail pipe, which leads the gases to the rear, the side, or more rarely to the top of the vehicle.

Sometimes twin parallel exhaust systems are used, especially with multi-cylinder engines, whilst it is also becoming increasingly common for two silencers in series to be fitted, the second and shorter unit being located immediately before the final outlet.

The exhaust gases leave the cylinders of an automobile engine at a pressure of around 60-80 lb. per sq. in. and with a velocity of up to 150 ft. per sec. This results in a considerable volume of noise, which must be reduced sufficiently to make the vehicle inoffensive to the driver and passengers, and to the public at large. This legal requirement is achieved by allowing the gases to expand into a silencer chamber, where the intermittent and violent discharges of gas are broken up and emerge from the tail pipe as a continuous and relatively uninterrupted stream.

There are various designs of silencer, but they usually contain a number of baffles carefully designed to avoid excessive back pressure, which might result in a loss of power and overheating of the engine. There is always some loss of power resulting from the use of a silencer, but this need not exceed about 3% with a well-designed unit.

• » Continue reading or Comments (13)

I’ve just returned from an interstate holiday. Originally from South Australia, my wife and I recently flew back to that state for ten days.

In addition to catching up with family and friends, I also wanted to do some riding. I broke-down my self-built, recumbent, full suspension, pedal trike so that it could be placed in a box for freighting the thousands of kilometres. Because I didn’t want to spend a lot of time reassembling, the box was pretty bloody large.  The cost of interstate freighting was not inconsiderable – but I am still very glad I took the trike.

My home Queensland terrain comprises steep and fairly rough bitumen roads. Most of the roads have no gutters – they’re rural and semi-rural roads. I might be inching my way up a 15 per cent grade one moment, pedalling in bottom gear – and then barrelling down the other side in 81st gear the next. I think the roads are very demanding of recumbent trikes: in fact, it was unhappiness with a commercial non-suspension trike that caused me to start to build my own machines.

• » Continue reading or Comments (1)

The other day I was looking at energy-efficient house designs.

Not having looked at off-the-shelf designs for quite a while, I expected to see plenty of houses integrating technologies that have been known for decades (and in some cases, centuries!); technologies like the use of wide eaves, northerly-facing windows (in our Southern Hemisphere), large thermal mass, solar-forced ventilation and so on. However I was amazed to see how few mainstream Australian builders appear to have any idea of these fundamentals of architecture.

Thinking about these aspects of energy-efficient house design reminds me of a building that I once constructed. Well, perhaps ‘building’ is a term with too much weight.

In fact it was a cat kennel.

Cat kennel? Yup – and the cat loved it. 

Designed specifically to provide a measure of solar winter heating, it comprised an insulated double storey timber dwelling, fronted top to bottom with a pane of glass. The cat didn’t have access to the lower storey – instead, that area was completely taken up by a 20-litre (5-gallon) steel drum, filled with water and painted black. The drum sat on some bricks, which were also painted black. The water and bricks gave the 1-metre high building substantial thermal mass.

• » Continue reading or Comments (10)

Yesterday Ford took the wraps off the new FG Falcon.

New Australian developed and built cars come along only very rarely; Ford took the unusual step of releasing the car on a Sunday so that it could gain precious free airtime on the Sunday night TV news and in the Monday papers.

Away from my home base, I watched the Sunday night Channel Nine TV news in Adelaide with interest. How breathlessly and non-critically would they report the release of the new car?

The report was relatively short but it was what followed that had me gobsmacked.

Immediately after the report on the Falcon finished, the Nine news moved straight to a segment on the booming sales of the hybrid Toyota Prius, and the way in which some individuals are now converting their cars to battery electric power. The station interviewed several Sydney electric car enthusiasts and presented a glowing report on the cars. Phrases like ‘fuel economy’, ‘greenhouse gas emissions’ ‘oil consumption’ and ‘cost to run’ sprinkled the report.

The juxtaposition couldn’t have been a bigger slap in the face for Ford: even the dimmest viewer could not have missed the implicit comparison.

Today, on the Monday after the Falcon’s release, my emailed News.com.au update doesn’t have a single mention of the new Falcon.

Imagine how different the news reports would have been if Ford had released a car with breakthrough fuel economy and lower greenhouse gas emissions. A turbo diesel engine, or a downsized six cylinder turbocharged to gain efficiency.

Instead we have launch control – and even more power, torque and weight. Oh yes, and a fuel consumption improvement that is nominal to say the least.

It’s very hard to believe that the Falcon will not go the way of the Mitsubishi 380 – and for much the same reasons. High quality engineering directed in completely the wrong direction, aiming at a target that started to move a decade ago and has now gone…

(See also this blog)

• » Comments (77)

If you live in an area that has a hot, wet summer, you’ll be all too familiar with the nightmare of tools rusting.

That’s especially the case if you have machine tools that have unprotected ground surfaces – like the bed of a lathe or a milling table. But even low-priced tools like drill presses have unprotected columns and chucks.

Leave the tools for a few weeks in these climatic conditions and you’ll find a veneer of surface rust. Leave them for a month or two and the rust will have started to bite into the surfaces.

The problem is even greater if you’re not using the tools on a daily basis. The more often you use the tools, the more likely that there will be oil and other lubricants being applied, so protecting the surfaces from corrosion.

• » Continue reading or Comments (2)

So Mitsubishi’s Adelaide car manufacturing plant is to close. The Mitsubishi 380, the large sedan released in 2005, has proved to be a flop.

Now, and over the next few months, there will be a prolonged post mortem, analysing the reasons why the car failed. Already, I’ve seen statements excusing Mitsubishi Motors Australia from culpability for its failure.

But to anyone not wearing rose-coloured glasses, manufacturing by Mitsubishi in Adelaide has been doomed since the very day of the 380’s release. The company – perhaps driven by their masters in Japan – made the atrocious decision to build and release a car that had no market.

And this is not a retrospective, wise after the event, summary.

• » Continue reading or Comments (16)

I am starting to wonder how much people should spend on tyres.

Years ago, when I owned a Subaru Liberty RS, I bought a set of sticky track tyres of the type that were only just road legal. They gripped phenomenally well, even in the wet. Given the minimal tread depth, the latter was a real surprise to me.

And at other times I have also bought other very expensive tyres, largely being guided by brand name and word of mouth.

But now I am not sure that on cars of less than stratospheric performance, it’s worth spending a lot of money on tyres. Instead, I am starting to think that if there are problems with handling, the money should be spent on the suspension instead.

• » Continue reading or Comments (11)

The (repeated) articles that we’ve recently run in AutoSpeed on power and torque are vital to understanding how to make your car go harder.

(The series can be found at Power vs Torque Part 1 –  and Power vs Torque Part 2)

And why is this understanding vital? Simply because people who use the terms ‘power’ and ‘torque’ often don’t seem to really understand what the words mean. The vital point to realise is that engine power is worked out by multiplying torque by revs.  And that’s the only way that power is worked out!

So an increase in torque at – say – 2500 rpm will mean a proportional increase in power also occurs at 2500 revs. It’s therefore just plain stupid to say “there wasn’t any change in the power curve but we got an increase in mid-range torque…” as some manufacturers of performance equipment state.

• » Continue reading or Comments (2)

Most cars that I have owned have had tow-bars – if they’re not on the car when I buy them, I have them fitted.

So the EF Falcon and Lexus LS400 both had towbars. And, as you’d expect with those cars’ mass and power, both towed very well. On one occasion the Lexus towed a camper trailer, and it very often towed my 6×4 steel trailer. The Falcon towed the 6×4 and once a car-carrying trailer (loaded with a large work bench frame).

So when both of those cars had gone to new owners and I bought the Peugeot 405 diesel, I was pleased to see it had a towbar.

I didn’t – and don’t – expect to be towing big trailers; instead, my 6×4 will be the one usually hung on the back. Trips to the local tip, trips to pick up furniture, carrying around recumbent trikes – things like that.

But as a tow-car, the low-powered and light Peugeot is a very different kettle of fish to the Lexus and Falcon. For starters, the lack of ultra-low rpm torque (when the 1.9 litre diesel is yet to come on boost) makes it very hard to climb my very steep driveway with the trailer on the back. In fact, to do this, I need to thoroughly warm the engine and launch with a lunge at the slope. 

Once on boost, the mass of the trailer doesn’t cause much of a problem; performance is clearly down but with decent driving, it’s no drama.

But one aspect of the Peugeot as a tow car amazes me. And what’s that?

The fuel consumption!

The presence of the trailer makes a radical difference to have much diesel the Pug drinks. Even with the trailer empty, consumption is up by 20 – 30 per cent. One reason for this is that the trailer adds about 25 per cent to the mass; another reason is that the trailer is much less hidden in the aerodynamic wake of the smaller car.

Clearly the idea that towing a trailer increases fuel consumption is not something new.

However, as more people drive cars like hybrids (incidentally, no Prius is factory certified for a tow bar) and smaller engine diesels, trailers designed with more than utilitarian cheapness may become attractive. A smaller, light-weight and aero-shaped trailer would, I’m sure, make far less difference to the Peugeot’s towing fuel consumption…

• » Comments (15)