New Cars - BMW's 24-Valve "Baby" Sixes

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A New Chapter

When you are a car manufacturer, it must be very difficult introducing a new engine. Everyone is interested in a new model, and so it is not difficult to spread the word about it, but when the innovation is under the skin, you can almost hear the audience yawn from the footlights. And yet the development of a new engine or gearbox will run into millions of pounds. At the Motor Show, BMW introduced two new 24-valve engines, but the announcement was somewhat muted against a background of new models. Nothing beats the arrival of bent metal beaten into a new shape.

At the moment these engines, a 2-litre and 2.5-litre, are only to be found in the 5-series, but will take a more public bow in the new 3-series arriving very soon. Their presence in both the 520i and 525i, though, is being kept very discreet for there is neither badging nor decal to give the game away. For all the owners of post June ’88 (new 5 series shape’s arrival in Britain) and pre-November ’90 520is and 525is, this must be good news, for they will not suffer too much in the secondhand market, but for the owner of a new model with the multi-valve, it is not such good news — you’ve got nothing to show off about.

So what is this new engine? Is it a conversion to the head only or have BMW gone the whole hog and created a new unit? Well, to answer the latter question first, BMW have swallowed hard, considering the popularity of the 13-year old 12-valve units, and come up with a completely new engine, albeit with the same cubic capacity. Why? There was only so much further the older engines could be developed, and one has to bear in mind that with tougher American and European legislation demanding cleaner and more fuel efficient cars, BMW needed a more state of the art unit as a base from which further developments could be made.

At its most basic, BMW have presented a 24-valve, twin-cam unit which develops a little more power, and yet is more fuel efficient and had been designed from the word go to be altogether friendlier to the environment.

The 24 valves nestling in the head are driven by cup tappets with hydraulic play-compensation units while the two camshafts are driven separately by single-row, maintenance-free chains. The six spark plugs are located between the two cams and have their own individual coil. All this is done in the name of reliability and easier servicing.

Other features include a plastic intake manifold with ultra-smooth intake walls, a cast cup-type flywheel on the 2-litre and a two-mass flywheel on the 2.5, and a torsional vibration damper for greater refinement. Most importantly, though, is the arrival of a new engine management system, BMW’s M 3.1 Digital Motor Electronics, without which the engine could not function. In both the 520i and the 525i the engine has been tilted over at an angle of 30 degrees to the right so that the bonnet does not have ugly and unaerodynamic lumps and bumps on the top.

Despite the extra size and extra valve gear needed to drive both camshafts and 24 valves, the new units weigh only 12 kgs (26 lbs) more than the units they replace, but both produce substantially more power. The 2-litre now develops 150 bhp and the 2.5-litre 192 bhp, 21 bhp and 22 bhp more respectively than the superseded units. This is reflected in the cars’ performance figures which show that the 520i has a top speed of 131 mph and can accelerate from 0-62 mph in 10.6 secs and the 525i a top speed of 143 mph and an acceleration figure of 8.6 secs.

Torque figures are correspondingly increased with the 520i being 140 lb ft at 4700 rpm and the 525i’s 181 lb ft at 4700 rpm, an availability which made an 800 mile journey from London to Salon de Provence all the more relaxing. It was the smoothness of the unit which impressed most, though, the 2.5-litre we were driving never obtruding into the cabin. The new 24-valve engines have moved the 5 series even further up the executive class scale. Economical? Well, we found that we were returning an mpg figure that was between 24 and 25, the tendency being towards the lower figure. Considering that the great percentage of the journey was on the autoroutes at speeds in excess of 90 mph, in fifth gear which in the new gearbox is not an overdrive ratio, petrol consumption would not figure high on the list of buying priorities.

On the other hand, if you want the status of a 5-series BMW sitting outside your house, fuel consumption, unless awful, would not be a major consideration, but things like image, comfort and a certain amount of performance are, and in all three areas, the new small six 5-series deliver.

For those who like to take their comfort a little further so that they do not have to change gear, BMW have proudly announced their new 5-speed automatic box, the first such production unit in a saloon. We only had a short journey in a 525i with this box, and although not this reviewer’s cup of tea, the benefit of such cars in urban driving is well appreciated. BMW even claim that the automatic models are more fuel efficient than the relevant manual versions.

Equipped with three options — “sport”, “economy” and “winter” — I found that it was worthwhile keeping it in the less economical “sport” mode, where fifth is hardly selected, to stop the constant changing gear. After a while it becomes decidedly irritating as it hunts around for a gear.

As you would expect, the new models do cost a little more than the superseded ones, so that prices are now £18,915 for the 520i, £20,840 for the 520i Special Equipment, £22,490 for the 525i and £24,200 for the 525i Special Equipment. The automatic option costs £1315 on all models. WPK

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