The Mercedes-AMG A45 has only been around for a couple of years and yet, it’s already been the recipient of a facelift. That’s what happens when you belong in a segment as competitive as the premium hot hatchback market. As competitive as automakers like Mercedes, Audi, and BMW are, the same holds true for aftermarket tuners, especially those who specialize in any of these three German brands. Such is the case with Posaidon, which is following up the release of its RS850+ tuning kit for the Mercedes-AMG E 63 by introducing the RS450+ program for Mercedes’ resident performance hatch. The tuner claims that it can squeeze out 500 horsepower and 409 pound-feet of torque out of the AMG A45’s turbo four engine, making it one of the most powerful kits for the AMT hatch.

Posaidon may not be as much of a household name as Brabus when it comes to Mercedes tuning, but it does have a penchant for delivering the goods. It proved as much when it presented the RS850+ program last month and this particular program has the tools to be a worthy follow-up. There’s not much in the way of other upgrades for the AMG A45, but there is that impressive engine upgrade, which ought to be worth the price of the whole kit considering how much extra power it can provide to performance-hungry owners of the hot hatch.

The tuner does have other services to offer, most of which are available on a per request basis. That might not be an ideal setup for some owners, but for those looking to really customize their AMG A45s to fit their personalities, it’s a chance to really stamp some identity into those premium performance hatchbacks.

Continue after the jump to read the full review.

Exterior

The RS485+ program appears to strictly be an engine upgrade program but it a closer investigation reveals that Posaidon is also offering some complementary pieces on the exterior, including a large rear wing and a choice of new Evolution alloy wheels ranging from 18 to 21 inches. The wheels, in particular, can be fitted with high performance tires to maximize the engine program of the hot hatch.

Interior

Note: Interior from 2015 Mercedes-AMG A 45 4MATIC shown here.

There’s nothing in the way of typical upgrades to the interior, but again, browsing Posaidon’s website reveals that the tuner is capable of doing some encodings and TV unlocking, not to mention hardware and software installations

Drivetrain

Note: Standard engine from 2015 Mercedes-AMG A 45 4MATIC shown here.

This is where Posaidon really put its full focus and it shows considering what the tuner was able to get out of the AMG A45’s turbo four engine. Taking full advantage of the increased power brought about by Mercedes’ facelift of the model in 2015, Posaidon decided to replace the hot hatch’s stock turbocharger with a ball bearing race version to increase the gas flow required to achieve its target output. Together with the bespoke larger turbine, the tuner also added impeller wheels and a gas-flowed scroll housing and used a higher boost pressure to process the required amount of air pressure to accomplish its goal. Improvements were also made to the air intake system as Posaidon installed a high efficiency intercooler and a low restriction air filter.

From there, the tuner wound everything together through modifications made to the engine and transmission software, bringing the total output of the AMG A45 to 500 horsepower and an electronically limited 409 pound-feet of torque. This results in an improved 0-to-60-mph sprint time of 3.5 seconds to go with a new top speed of 196 mph, enough to make a Posaidon-tuned AMG A45 one of the fastest and most powerful hot hatchbacks in the business.

It should be noted that this engine conversion isn't just limited to the AMG A45. All Mercedes units that use the M133 engine, including the AMG CLA45 and AMG GLA45 can also get the same tuning program.

Chassis and Suspension

No word about this section on the press release, but the tuner’s website reveals that it’s open to chassis and suspension upgrades, including the addition of racing stabilizers that helps improve handling and achieve higher cornering speeds. Spacers are also being offered as are adjustable aluminum support bearings. It must be noted that the availability of each of these components depends on the vehicle model.

Pricing

Pricing details were also not revealed. That puts the onus on interested customers to request a price quote from the tuner directly to determine the exact amount of the program, or at least the upgrades that customers may choose to get from Posaidon.

Competition

Mercedes-AMG A45 by Brabus

There have been a few tuning programs built for the Mercedes-AMG A45, one of which came from Brabus. No surprises there. The German tuner presented its kit back in 2014 and it came with a series of enhancements, none more important than the PowerXtra electronic kit given to the AMG A45’s 2.0-liter turbocharged four-cylinder engine. It resulted in an output of 400 horsepower and 369 pound-feet of torque, which isn’t much now that Merc has given the A45 381 ponies to play with. Still, it comes by way of Brabus, which in itself is something worth mentioning.

Find out more about the Mercedes-AMG A45 by Brabus here

Mercedes-AMG A45 by Vath

Yet another one of the early bird tuning kits for the AMG A45 was this program developed by fellow German tuner and fellow Merc tuning extraordinaire Vath. Just like Brabus, Vath unveiled this kit back in 2014 when the AMG A45 still had 360 horsepower and 331 pound-feet of torque. The hot hatch has since seen its output increase to 381 horsepower and 350 pound-feet of torque, but that still shouldn’t take away from what Vath put into the hot hatch when it was able to ring up a total of 425 horsepower and 387 pound-feet of torque out of that turbocharged engine. The tuner accomplished that and in doing so, it was able to drop the car’s sprint to 60 time to just 4.2 seconds to go with a top speed of 174 mph.

Find out more about the Mercedes-AMG A45 by Vath here

Conclusion

There are other tuners that offer more on a quantity level – more exterior upgrades, some interior upgrades, even a menu full of wheel choices. Posaidon isn’t one of those tuners. But when it comes to engine upgrades for the AMG A45, the tuner isn’t prepared to take a back seat to anybody and if the RS450+ engine upgrade package is any indication, it may not have to. It’s one of the most powerful performance modifications for the AMG A45 to date, and it’s a good example of a program that speaks the language of power.