One of the things I enjoy about reporting motoring news is spotting ideas that have been tried before. Last week I was writing about the Mercedes-Benz C-Class BlueEFFICIENCY range. One feature of the frugal Merc that didn’t warrant a mention in the article was the back-to-front layout of the engine.
Just about every car engine has the drive for the camshaft at the opposite end of the engine to the clutch and flywheel. For the new diesel motor Mercedes placed the camshaft drive at the back of the engine. Justification for the layout is to provide a little more clearance under the bonnet for pedestrian protection.
Mercedes isn’t pretending that the layout is a new invention but it did remind me that several engines back in the early days of motoring used a similar configuration. The example that comes to mind immediately is AC’s long-lived 2.0-litre six-cylinder motor. The one question I have over the layout is what happens if you need to change the chain that drives the cam shaft?
Friday, 19 September 2008
Sunday, 14 September 2008
BX update
Fourwheelsteer’s faithful if sometimes fallible Citroen BX has received some long overdue care from the good people of Preservation Garage Services (PGS) in Warwick. The same people who did such a good job of looking after my old BX performed a service and changed the cam belt and the car seems better as a result. There may be nothing measurable – it is too early to see if fuel economy has improved and I’ve not tried to measure acceleration or top speed – but the engine sounds sweeter and feels more willing.
A 1,360cc engine in a large-ish hatchback body might not seem like the perfect recipe for driving enjoyment but the BX only weighs 900kg so the 72bhp motor does not have to work too hard. The power unit is abetted in its task by a five-speed gearbox with ratios perfectly judged to make the most of the engine’s efforts. Although the overall gearing feels rather low – there is no rev counter to verify this assumption – there are no noticeable gaps between gears. The result is that there is always a gear that is right for the occasion.
Sadly, the merits of well-spaced gear ratios are being abandoned by manufacturers for the sake of fuel consumption and carbon dioxide figures. Several times this year I have read boasts of making the top three gears in a five-speed gearbox higher whilst leaving first and second alone – what can this do except leave a big gap between second and third gear? It probably fits the strictures of the standard test procedure perfectly but our roads are not standardised and on the road there will be times when the choice is stream or strain, neither of which is ideal.
This isn’t a new problem; the industry has been producing oddly geared cars for as long as it has been producing cars but it can make a big difference between enjoyment and frustration when driving. If you want a car with perfect gearing all the time surely you need some sort of continuously variable transmission.
A 1,360cc engine in a large-ish hatchback body might not seem like the perfect recipe for driving enjoyment but the BX only weighs 900kg so the 72bhp motor does not have to work too hard. The power unit is abetted in its task by a five-speed gearbox with ratios perfectly judged to make the most of the engine’s efforts. Although the overall gearing feels rather low – there is no rev counter to verify this assumption – there are no noticeable gaps between gears. The result is that there is always a gear that is right for the occasion.
Sadly, the merits of well-spaced gear ratios are being abandoned by manufacturers for the sake of fuel consumption and carbon dioxide figures. Several times this year I have read boasts of making the top three gears in a five-speed gearbox higher whilst leaving first and second alone – what can this do except leave a big gap between second and third gear? It probably fits the strictures of the standard test procedure perfectly but our roads are not standardised and on the road there will be times when the choice is stream or strain, neither of which is ideal.
This isn’t a new problem; the industry has been producing oddly geared cars for as long as it has been producing cars but it can make a big difference between enjoyment and frustration when driving. If you want a car with perfect gearing all the time surely you need some sort of continuously variable transmission.
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