At what point does a hot hatch become a pint-sized sports car? The Mercedes A45 AMG was already blurring the line, but the engineers over at AMG's Affalterbach headquarters decided that the pint-sized turbo terrier needed more power. Thanks to an extra 15 kW (20 hp) from its 2.0-liter motor, the updated A45 AMG will now hit 100 km/h (62 mph) in just 4.2 seconds.

In addition to boosting the power to 280 kW, the A45's engine peak torque is up 25 Nm to 475 Nm while shorter gear ratios help the car bolt out of the blocks harder than before. Engineers have found the extra power by fitting a new valve assembly and tweaking the engine timing. Mercedes also says that changes have been made to the way the turbo operates, but maximum boost pressure remains set at 1.8 bar.

Thanks to AMG's changes, which should return better throttle response than that offered by the original A45, the car has also raised the game for anyone hoping to steal its crown for highest specific output from a four-cylinder engine, bumping it up to 141 kW (191 hp) per liter.

In spite of the extra punch, the A45's claimed fuel economy is unchanged at 6.9 l/100km (34 mpg). As before, the chances of actually achieving that figure are extremely slim, as anything but a feather-light touch on the throttle tends to make heavy drinkers of performance engines.

To make sure the car's stable handling isn't upset by the extra power and torque, Mercedes is now offering a mechanical locking differential on the front axle that works in tandem with the 4MATIC all-wheel drive system to drag the car out of low-speed corners and slingshot it off into the distance.

It might be the entry point into the AMG club, but the A45 hasn't missed out on the driver configuration tech from the C63 AMG and AMG GT. Owners can tailor the feel of their cars between Comfort, which defaults to high gears for improved economy, Sport and full-fat Sport Plus modes.

If these changes seem superfluous on what was one of the quickest hatchbacks around, it's worth bearing in mind the Audi RS3 has just dropped with a 0-100 km/h (62 mph) time of 4.3 seconds ... so that looks like a point for Mercedes.

The A45's upgrades are a part of a wider midlife refresh on the A-Class lineup, which includes the introduction of an ultra efficient A180 d BlueEfficieny model that sips just 3.5 l/100km (67 mpg) from its 1.5-liter engine. CO2 emissions are just 89 g/km.

If you're keen to show the world that you love F1, the new A Class will be available in a special Motorsport Edition, which is finished in a similar paintjob to that on the brand's championship-leading F1 cars. Oddly enough, however, the Motorsports Edition package can't be fitted to the car with the most motorsports connection in the range: the A45 AMG.

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