Don’t be fooled by its curious looks; there’s a monster lurking underneath all that pomp

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This is a Mercedes-AMG A45 S, or at least it used to be. Don’t be fooled by what you see here; It still looks like the AMG A45 S, but underneath that bright yellow paint, black decals, and gimmicky taxi lamp on the roof lies a different beast altogether - one that’s going to rip your heart out the second it gets the chance. This used to a Mercedes-AMG A45 S. Now it’s called the Posaidon A45 RS 525, and best be warned, “mercy” is not in this hot hatch’s vocabulary.

What’s so special about this tuning program for the Mercedes-AMG A45 S?

2020 Posaidon A45 RS 525 Exterior
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There’s a reason why this sexy piece of hatch is called the Posaidon A45 RS 525.

The Posaidon A45 RS 525 is an exercise in possibilities. The Mercedes-AMG A45 S, in stock form, is powered by by the mind-bending 2.0-liter turbocharged M 139 four-cylinder engine that produces 412 horsepower and 368 pound-feet of torque.. Not only is it the most powerful four-cylinder engine in the world, but there’s also enough room for an aftermarket tuner who knows a thing or two about building tuning programs for Mercedes models to squeeze more power out of that ‘thang.

2020 Posaidon A45 RS 525
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In order to reach its desired output, Posaidon used its tried-and-tested engine remapping software and dropped an upgraded turbocharger into the powertrain setup.

2020 Posaidon A45 RS 525
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With all the upgrades in place, the twin-turbo M 138 four-pot now produces 525 horsepower and 442 pound-feet of torque, sent to all four wheels courtesy of an equally new eight-speed dual-clutch transmission. Posaidon notes that the RS 525 — that’s how it got its name — is capable of sprinting from 0 to 60 mph in just 3.4 seconds, making it faster to 60 mph by almost half-a-second compared to the standard AMG A45 S. The fun doesn’t end there, either. The RS 525 maxes out at a speed of 201 mph. That’s an increase in top speed of 15 mph compared to the standard hot hatch.

2020 Posaidon A45 RS 525
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Of course, none of those numbers matter if the car can’t carry its own weight at those speeds. Posaidon neatly addressed that aspect, too, with a track tool upgrade that includes two-way adjustable coilers and larger 14.25-inch brakes with steel flex lines. The tuner even threw in racing harnesses for the front seats and a full-on roll cage at the back in lieu of the rear seats.

It’s an impressive aftermarket setup for an impressive hot hatch that still has AMG blood running in its veins. The Posaidon A45 RS 525 offers a taste of what’s possible with the right setup and the right tuner behind it.

How Much Does the Posaidon A45 Cost?

2020 Posaidon A45 RS 525 Exterior
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Posaidon didn’t reveal pricing details of the RS 525 kit, though don’t expect it to come cheap. Turbochargers alone will easily set you back four figures, and that depends on the type and quality you’re buying. Spoiler alert: there’s nothing cheap about Posaidon’s programs so don’t expect its turbocharger to cost for anything less than the amount that’s in your head now.

Then there’s the car itself, which you may or may not have in your possession already. If you already own a Mercedes-AMG A45 S, then good for you. If not, it’s probably important to know that the high-powered AMG hot hatch starts at £50,750. That converts to around $61,390, though it hardly matters since the AMG A 45 S isn’t available in the U.S. market. Tough sledding for us, but at least we have the AMG CLA 45.

Final Thoughts

2020 Posaidon A45 RS 525 Exterior
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It’s hard not to be impressed with what Mercedes-AMG has with the AMG A 45 S. It’s already more powerful in standard form than it has any business of being, and yet, there’s apparently still more to it than what AMG is offering. It helps, too, that the tuner on the job is Posaidon. Posaidon has years of experience and receipts to back up its ability to turn proper hot hatches into full-blown compact wreckers of open roads. Trust in Posaidon with an AMG program. You won’t regret it.

  • Leave it
    • Not sure about those decals
    • AMG A 45 S isn’t available in the States
    • 525 horsepower could be too much for some to handle
Kirby Garlitos
Automotive Aftermarket Expert - kirby@topspeed.com
Kirby’s first exposure into the world of automobiles happened when he caught Knight Rider on television as a five-year old boy. David Hasselhoff didn’t leave much of an impression on him (that happened later on in Baywatch), but KITT certainly did. To this day, Kirby remains convinced that he will one day own a car with the same ‘spirit’ as the original KITT (not the 2008 monstrosity). He doesn't know when that will be, but until then, he’s committed to expressing his love for KITT, and all cars for that matter, here at TopSpeed.  Read More
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