SINCE the dawn of prohibitive road taxes here, most car buyers have deferred to a kiasu but nonetheless sensible dictum when shopping for a new set of wheels - big body, small engine. This rule of thumb means that a nice big car with an engine capacity that slots neatly into a lower tax bracket is always preferable to the same model with a bigger block and more satisfying power.

So it should come as no surprise that the new BMW 520i with a two-litre engine has been receiving much curious interest since it was launched in Singapore last month. Until now, the current generation 5 Series has only been available with engines larger than two litres, like the 523i and 525i with 2.5 litre units, and the 530i with a three-litre powerplant.

When this particular model of the mid-size 5 Series was first introduced here in 2003, there was a 520i. But this actually had a 2.2 litre inline six-cylinder engine (it was eventually phased out in 2005). Only the 520i from the previous generation had a bona fide 2.0 litre engine.

If all that sounds unnecessarily complicated, there's another twist - this new two-litre 520i has a four-cylinder engine.

This is the first time that a 5 Series for our market has not had a straight-six engine. There was a 518i from two generations ago with a 1.8 litre, four-cylinder engine. But it was meant for certain European countries and was never introduced here.

A four-pot may be derided by diehard Beemer fans, for whom only the highly acclaimed straight-six will do. But the 520i is surprisingly refined for a four-cylinder unit. It doesn't make itself heard as much as in the 320i, which has the same engine.

However, this enhanced smoothness is probably due to revised engine management, different gearing and the better insulation of a bigger car.

As for power, the 520i seems more adequate than would be expected. It seems to set off as enthusiastically from a stationary start as a bigger 5 Series. But it is clear that it lacks the bigger lungs and elasticity of its nearest variant, the 523i.

Floor the gas pedal while trying to initiate an overtaking manoeuvre and all your kickdown will achieve is an increase in sound levels. This flat spot is due to the 34 hp deficit compared with the 523i. The 520i also has 30 Newton-metres of torque less than the bigger, six-cylinder model.

The 520i also has a shorter list of standard equipment. It doesn't have the dual-zone aircon system or the cruise control of the 523i. Other features missing include the latter's bigger alloy wheels and electric rear roller sunblind.

But the benefits are obvious. For one, there is the lower sticker price, as well as the smaller bills for road tax and petrol. The 520i is a substantial $20,000 cheaper than the $183,800 523i. Yet it has the same dynamic abilities as any other 5 Series, along with the same sporty six-speed Steptronic gearbox.

Then there is the mid-size body. Apart from being more spacious inside than a compact 320i, the 5 Series has more presence on the road. There's something to be said for being kiasu after all.

BMW 520i
Engine: 1,995cc inline-4
Gearbox: 6-speed automatic transmission
Max power: 156 hp @ 6,400 rpm
Max torque: 200 Nm @ 3,600 rpm
0-100 kmh: 10.6 secs
Top speed: 219 kmh
Price: $163,800 (with COE)
Distributor: Performance Motors, tel 6319-0100

This story was first published in The Business Times on Mar 1, 2008.