The Globe and Mail

Here is the question: why do you need 617 horsepower in your everyday commuter car?

The answer: To hit 338 km/h (210 mph) in a handful of seconds.

Of course, in Ontario if you get caught doing this, they'll take away your car. They'll throw you in the clink, throw away the key and post your face on billboards as a dangerous offender. Jail is scary, but losing the car is a nightmare for the owner of a 2009 SLR McLaren Roadster with a sticker price of a cool half-million. American dollars, that is.

It is possible the SLR will be worth more than that some day; this year marks the end of a production run of about 500 cars a year, so there are few of them and no more in the works.

Rare cars usually increase in value over time. But rare cars from a company - Daimler AG and its Mercedes-Benz brand - that loves its racing and its racing heritage, and loves to prove it with specialty cars in small numbers? Another thing entirely.

This, of course is the purpose of the SLR - which stands for Sport, Leicht, Rennsport in German (sport, light, racing).

Mercedes and its racing partner, McLaren, got together in 2005 to build something that evokes the 300SLR of old and the Formula One McLaren of the now. The SLR - the 0-100 km/h in 3.8 seconds SLR, the SLR with an engine that roars like Thor (the god of thunder) on a Saturday night rampage - is the result.

While the SLR roadster I've just been driving is a two-seater with half-scissor, half-gullwing doors, this is not a small, lightweight Italian runabout. No, the SLR may have a rigid, high-tech, wildly expensive carbon fibre structure, but it's no lightweight at 1,768 kg and it's not small, either.

Moreover, while the flat bottom, front and rear diffusers, and a tail spoiler designed to provide down-force at speed make the SLR stable when going flat out - not to mention amazingly nimble in the turns - there is a downside: you need big horsepower to get it moving and keep it there. A big, fast rear-drive car demands big gobs of horsepower.

This explains the fully-dressed engine from Mercedes' own in-house performance tuner, AMG, which McLaren further played with in England. At 5.5 litres, the singe-overhead-cam unit with three-valve heads is compact, yet it packs a wallop. The twin-screw blower - the supercharger - between the cylinder banks pumps up power to a fabulous 617 hp.

Oh, yes, this is a serious engine. You know this because it's housed astern of the front axle, making it a front-midship design. And you know this because the dry-sump lubrication system allows the V-8 to sit lower than a conventional oil pan allows - while also guaranteeing the bearings will not be starved for oil regardless of how many Gs you're pulling on the track.

Speaking of the track, did I mention the brakes? They are monstrous carbon ceramic jobs with eight-piston calipers squeezing 370-mm discs at the front. The more modest rear setup is comprised of four-piston calipers and 360-mm discs.

To help scrub speed, there is also a pop-up rear wing that acts like a miniature dragster-style parachute.

The SLR, then, is very close to a street-legal race car, yet Mercedes has baked in a serious measure of civility.

Standard are such grand touring amenities as a heated glass rear window, heated exterior mirrors, a semiautomatic fabric soft-top, six-way power carbon fibre sport seats, leather and Alcantara upholstery, aluminum trim, Bluetooth phone connectivity, dual-zone automatic climate control, adaptive cruise control and a seven-speaker Bose surround-sound system with a trunk-mounted six-CD changer.