201mph Mercedes-AMG A45 S tuned by Posaidon

421hp A45 S not mad enough? This one makes 518hp - or 260hp per litre...

By Sam Sheehan / Wednesday, 29 April 2020 / Loading comments

When AMG announced in 2019 that it had produced a 2.0-litre block capable of providing the new A45 S with 421hp, eyebrows were raised. Yet here we are, barely a year on from that moment, faced with a souped-up A-Class that one German tuner has extracted a frankly absurd 518hp from. Using essentially just two engine modifications, Posaidon has turned Affalterbach's M139 into a four-cylinder producing 260hp per litre. It now tops out at 201mph. Crikey.

That peak output, you may have noted, is 8hp more than the twin-turbo V8 of the C63 S, as well as 97hp better than the 'standard' A45 S. It's a lot of muscle by anyone's measure, but such is the motor's strength that the Koblenz-based firm has achieved that new max power and an accompanying 443lb ft of torque with only a new turbocharger and different engine control software. That's all that's been required to create a 200mph-plus hatchback.

Posaidon has, of course, also made tweaks to AMG's Speedshift auto to suit the enhanced punch, which has allowed the 0-62mph time to drop to just 3.4 seconds and the top speed to reach a remarkable 201 mph. You might have thought such statistics would edge the M139 motor and surrounding all-wheel drive hardware close to their limits, but apparently not: Posaidon claims to have a Plus model in the works with even more power and performance.

The firm does also offer a lower-powered upgrade that's focussed entirely on the ECU remap, upping output of the A-Class to a still impressive 465hp and 413lb ft of torque, with the 0-62mph dash taking 3.6 seconds - three-tenths better than the factory AMG A45 S. It achieves that without needing mods to the eight-speed auto as well, emphasising the strength and engineering capacity of the standard equipment aboard Mercedes' ballistic five-door hatch. And the warranty? We're making enquiries...