The topic of bump stops does not attract much interest. But especially in cars with lowered suspension, and in light-weight cars, bump stops form an important part of the springing system.

A bump stop is the (usually) rubber buffer that is compressed as the suspension reaches full bump. (Some cars also have full droop buffers as well.)

Traditionally, bump stops were impacted only rarely, but more and more often in current cars, the suspension is designed in such a way that the bump stops are frequently contacted.

Let’s look at light weight cars first.

In a light weight car, the variations in possible loads make up a greater proportion of the overall vehicle mass. This means that, to avoid bottoming-out, the suspension must be set up more stiffly to cope with the potential load variation.

Or – and here’s the key point – the bump stops can be designed to be increasing rate (but still relatively progressive) springs that are brought into operation when the car is carrying full loads over bumps. That way, the spring rate of the suspension during ‘normal’ load carrying can be set much softer, giving a better ride.

• » Continue reading or Comments (4)

Orville and Wilbur Wright were genuine engineering heroes. Despite their relatively humble beginnings, these men were the first to ever to build – and then successfully fly – a powered aircraft.

I’ve often read descriptions of their brilliance that damns them with faint praise: they were ‘just bicycle mechanics’, their work built heavily on the efforts of others, and so on.

In fact, they were simply brilliant engineers, with an astounding work ethic and the ability to both physically make things and also theorise about outcomes.

Unless you think I overstate the brothers’ abilities, consider these points… They built their own wind tunnel and tested in it almost 200 wing sections; they built an internal combustion engine with the then best power/weight ratio of any engine in the world; they made every part of their own aircraft – from that engine through to propellers to wing and control systems; they developed the concept of an aircraft banking into turns – and a lot more. 

• » Continue reading or Comments (4)

The more you think about turbo boost control, the more implications there are for any given system.

Let’s just refer to a traditional wastegate system.

(That’s where there’s a bypass passage – the wastegate – around the turbine. Open the wastegate and exhaust can bypass the turbine, slowing turbo speed and so dropping boost pressure. Remember – the less open the wastegate, the higher the boost pressure.)

In this discussion it doesn’t matter if it’s an electronically controlled system or a simple pneumatic system.

Let’s say that boost pressure is sensed from the compressor outlet of the turbo. If the maximum desired boost is 10 psi, the maximum outlet pressure of the compressor will also be 10 psi.

But the situation changes if the boost pressure is sensed from the intake manifold. If 10 psi is again desired, the boost pressure at the manifold will be 10 psi, but the boost pressure being developed by the turbo will need to be higher.

• » Continue reading or Comments (6)

I’ve just returned from a week on the road.

The vehicle of choice was my recumbent pedal trike, a design that you can read more about here and here. (In the pic above I’ve just finished my ride, so explaining the wrong shoes.)

I left Gold Coast and went to Tallebudgera, Pottsville, Byron Bay, Lennox Head, Yamba and then Grafton – mostly in northern NSW. Carrying full camping gear, I stayed each night in local caravan parks, spending one night in each except at Yamba where, because of steady rain, I spent two nights.

My last stop was at Grafton, where I got picked up by car and trailer.

Including diversions, I rode about 350 kilometres.

• » Continue reading or Comments (27)

The other day I bought some manuals published in July 1960. They’re lecture notes from the Technical Training School for Qantas Empire Airways Ltd.

The notes are primarily on the Lockheed Electra, an aircraft powered by four Allison 501-D13 prop jet engines. These engines each developed about 4000hp.

One of the very interesting technologies covered in the manuals is a real-time, on-board dyno. Yes, in the cockpit was a gauge that displayed the power being produced by the engine! This gauge was calibrated from minus 1000hp to plus 6000hp. Accuracy was quoted as being +/- 355hp.

So how was a real-time indication of power output gained?

On this turbo prop design – as with all turbo props that I’m aware of – a gearbox is used to reduce the speed of the turbine to that suitable for driving a propeller. The turbine is joined to the reduction gearbox by means of a driveshaft, splined each end. Surrounding this shaft is another shaft, this one splined only at the turbine end.

• » Continue reading or Comments (12)

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)

It’s perhaps the only car that I have always wanted – well, from the day of its release, anyway.

The year was 1988 and the BMW 750iL was an astonishing car – twin electronically-controlled throttles, 12 cylinders, a limousine that handled so well that contemporary magazine testers were able to triple advisory speed limit signs around corners. On just six of the twelve cylinders, it could still exceed 200 km/h…

I’ve watched and watched as their prices have fallen – in 1988 the cars were $216,000; each year since they’ve got lower. Now, they’re under $10,000.

Less than ten grand for what was amongst the very fastest of four door cars in the world, a superbly equipped, beautiful looking sedan from that long ago time when BMW styling still had grace and cohesion.

• » Continue reading or Comments (27)

I’ve been thinking about the way in which cars are heading. More and more these days you see driver-selectable modes. A sports mode – or even super sports mode – on a double clutch transmission. A button that sharpens throttle response, changes damping and alters auto trans shift points.

Two points.

Firstly, if the car drives badly when in standard mode, fitting a special button doesn’t fix the car. The ‘fix’ needs to be far more fundamental: at minimum, all modes need to drive well.

But the main point I want to make is this.

Why on earth are manufacturers giving only ‘digital’ control over this type of driver selection? Why an on/off switch when it would be far better to provide an analog knob that allows the driver to adjust the action of the system to their taste?

A knob for power steering weight.

• » Continue reading or Comments (11)

Look, I’ve tried to like it. I’ve admired its quite brilliant fuel economy, and its generally excellent ride/handling compromise. I mean, I was even very positive in the new car test I did on the car when it was first released back in 2003.

And when this family bought one with our own money, it was with the (stated) intention of making it an AutoSpeed project car, in much the same way that we did with the Peugeot 405 SRDT.

But I need to be honest. I just simply hate the Peugeot 307 HDi – I think it’s a car that in many ways is just rubbish.

Now normally to support such a statement you’d have an extensive list of shortcomings in its driving performance. But in fact, the Peugeot largely drives very well.

One clear negative is its dreadful low rpm management mapping and/or turbo sizing: this is one of the deadest off-boost turbo electronic direct injected diesels you can drive, especially in hot weather.

(I just checked the date of my original new car test – published November so probably tested about September. Just on the edges of the Australian summer – but not into it.)

But otherwise, the steering is largely OK (well, it kicks back when driving really hard); the ride is good; the handling is adequate and the brakes fine.

• » Continue reading or Comments (45)