YOU know the answer before you ask, but can't help yourself; when will the horsepower race end?

The answer, of course, is never. Or at least not until someone passes a law with a limit in mind.

Until then we'll continue to see cars like the latest Audi RS3 Sportback, which within its compact and practical shape packs a punch that will take the car to an astonishing 174mph, if you ask for the artificial speed limit to be switched off.

That costs £2,495 as part of an upgrade package on this £39,995 car. With the restrictor in place you will have to make do with a mere 155mph. Which ought to be enough for anyone, and only reachable (lawfully and moderately safely, anyway) on a derestricted German motorway at the crack of a summer's dawn.

More useful in everyday performance terms is the time this well equipped Tarmac terroriser takes to hit 62mph - the yardstick by which every car is measured, from shopping hatch to ground-pawing Lamborghini.

Well, this Audi takes 4.3 seconds. You couldn't pour a cup of coffee in that time, let alone look round to see if the Lambo is keeping up.

This is a mind bendingly fast car with the most powerful five-cylinder production engine in Audi RS history (and that layout has a lot of powerful history to call on). It produces 362ps and all that is pumped through every wheel thanks to its quattro all wheel drive set up and a seven speed auto gearbox.

This second generation A3 RS is, says its maker, the most powerful compact hatchback you can buy. It also costs more than a couple of other speedy Germans, in the shape of the VW Golf R (£32,890 in auto form) and the auto-only Mercedes-Benz A45 AMG (£38,195).

But crucially in the power race, both are less powerful than the Audi and both accelerate a little more slowly. We're talking blinks of eyes here, but in the rarified world of the hottest of hot hatches, fractions matter.

There can be little room for complaint about the Audi's equipment count. Apart from the serious engineering changes made to keep the car safe, reliable and (hopefully fun to drive) you will find big alloy wheels set in a body with flared wings, rear spoiler and touches of gloss black and matt aluminium to give visual clues to all that power.

Inside, there are gorgeous looking sports front seats covered in soft grey leather, alloy pedals, black faced instruments with red needles - even a lap timer for those daring adventures on the local race track. No satellite navigation as standard though, which looks mean at this price. A basic version is £495.

The power from the five-cylinder engine reaches the ground through Audi's quattro all-wheel drive system and an automatic dual-clutch gearbox, without the option of a DIY manual gear change.

Fancy disc brakes, more direct steering and specially adapted suspension are proof that Audi went much more than skin deep to produce this fire breather. Was it worth the effort, you now ask?

Well, yes. Even on badly pockmarked British roads the car gets a serious move on without feeling over firm, and feels surprisingly compliant in the firm, dynamic mode of the optional (£995) magnetic ride and sports suspension.

On the short but so demanding twists of the Shelsey Walsh hill climb course in Worcestershire, where Audi let us loose, it clung like a leech and hit 90mph at the end - on a track little wider than the car.

There is even a practical side to this car, with a big boot and room for two big adults in the rear, where the ride goes downhill a bit and coarsely surfaced roads set up a racket.

Up front, and especially at the wheel as the sports exhausts barks and pops in a racetrack way, your thoughts are on the road ahead, not the passenger sitting behind.

And for those who really think about every aspect, fuel economy is rate at 34.9mpg with emissisions of 189g/km - incredible for a car with such credentials.