The battle of the small, fast, premium, German hatches just went nuclear with Mercedes announcing a full blown A-Class AMG that’ll get the biggest guns of any production hot hatch on the road – a smouldering 355bhp, and a sub-5-seconds-to-62mph sprint time. But, it’s unlikely that BMW and Audi will toss out their turbos in despair. Let the forced induction firefight begin!

Mercedes A45 AMG Feature
Quicker than a Carrera!

If you’ve got around £40k to spend on a brand new car right now and you don’t have to worry about ferrying kids around or hauling giant boxes of crap from Ikea, then road-life is going to be pretty sweet for you. If you like your curries with a brow-sweating kick, you’re not scared of tequila or two, and you like your hot hatches quicker to 62mph than the new Porsche 911 Carrera, then Mercedes AMG have got a titanic treat for you. The 355bhp A45 AMG. It’s a hunkered down, carbon covered chunk of pocket rocket insanity, and will bear the honour of being the most powerful hot hatch when it launches in July.

Turbos are doing it all right now; mixing torquey performance with reasonable economy, and with manufacturers catching their petrol-turbos up with the same amount of R&D focus that diesel-turbos have had for the last several years, us fans of all things fast – yet potentially achievable with real-world pay packets – are starting to see some supercar-like performance figures from engines that are wrapped up in family-car-type bodyshells. It’s the era of the real-deal turbocharged road car and this new A-Class AMG is the first really serious gauntlet from a mass market manufacturer.

 

Terrific tech spec

This is the first small Merc to be fettled by AMG and they clearly wanted to make a statement. The A45 AMG’s tech spec reads like something from a top end tuning catalogue, and when you add up all the performance hardwear under that stocky-looking skin, at around £36k, it’s actually good value. Yes, I know it’s a lot of dosh, but 355bhp, a 7-speed double-clutch gearbox, forged engine, serious suspension and brakes, and a sumptuous leather interior is an impressive haul. Try building a hot hatch project car from scratch for £36k that looks this good and goes this fast. I’ve done it, and you can’t.

The key to the new king of the hot hatches is its engine, and this lightweight (148kg dry), 2-litre, 4-cylinder turbocharged motor is making a lot of shove from its 1,991ccs. A full 1.8bar (over 25psi) of turbo boost pressure makes the max power of 355bhp at 6,000rpm and a thumping 450Nm of torque from 2,250 – 5,000rpm. This enables the naughtiest small Merc ever to hit 62mph in 4.6 seconds – that 911 Carrera needs 4.8 seconds – and on to a limited top speed of 155mph.

All this hard charging turbo boost is why we need the tough forged pistons (with low friction rings), a forged steel crank, and a meaty air-to-water charge cooling system, that cools, and makes denser and richer, the engine intake air. Richer intake air means more fuel can be burned in it, and more power made.

The AMG engineers went for a single, twin-scroll turbo for their latest 2-litre terrorist, and it’s the latest in turbocharger design that lets the power outputs increase, in keeping with the same upwards trajectory that driveability and economy also need to take.

 

 Audi’s and BMW’s revenge…

Back in the day, if you needed your 1,991cc engine to make 355bhp, you’d put a big ass turbo on it to make a ton of boost. But, this large and ‘heavy’ turbo would barely move until the engine revs were high enough to make plenty of exhaust gas to spin its blades and then compress the intake air, so there would be no power until around 3,500rpm. A big chunk of turbo lag, basically.

The power would then hit hard and sexy at over 4,000rpm making for a wild ride, but can you imagine that kind of engine behaviour in a mass market, £36k Mercedes? It’d scare the hell out of your Merc driving aunty! The small and highly optimised twin-scroll turbo on this new AMG is delivering full torque from 2,250rpm, and a good dollop of go-go from even lower in the revs, too.

Surround this handbuilt powerplant with all the AMG knowhow for suspension, brakes, a quick-witted 7-speed double-clutch gearbox with four-wheel drive and a throttle-position-responding fruity exhaust, and we’ve got one wickedly spicy specification. But, rest assured the bhp-boffins at Audi and BMW will also be working hard with turbocharger producers to make the next step up in power and economy performance – this A-Class puts out an impressive maximum of 165g/km of CO2 with all that power – so don’t expect the A45 AMG to the hottest of hot hatches for too long.

 

By Dan Anslow

 

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