G-Power’s reputation is one of the foremost BMW tuners in the land. That reputation has laid the foundation for the German tuner to branch out to other automakers, including Bimmer’s crosstown rival, Mercedes-Benz. Take this program for the Mercedes-AMG GT 63 4-door, for example. In keeping with tradition, G-Power is presenting a three-stage engine upgrade program that pulls some sickening power and performance figures out of the AMG GT 4’s 4.0-liter twin-turbocharged V-8 engine. On top of that, G-Power’s new kit for the power-packed four-door luxury Merc-AMG also includes a new set of wheels and a smattering of other cosmetic upgrades that help elevate the AMG GT 4-door’s stature higher than where it’s already at. If you thought the Mercedes-AMG GT 4-door is the most subdued of all AMG GT models, then prepare to be blown away with what G-Power is offering for the high-powered sedan.

What's G-Power's exterior upgrade offering for the Mercedes-AMG GT 4-door?

G-Power's tried-and-tested tuning formula typically revolves around a slew of upgrades spread throughout a specific car. Cosmetic and aerodynamic upgrades are present, and while these upgrades vary depending on the model, it is a G-Power staple to maximize the overall potential of a car; it's building a program for. That said, it does come as a bit of a surprise to see that the tuner's exterior upgrades for the AMG GT 4-door revolve largely around a new set of wheels.

Not that we should take that against G-Power. After all, the tuner is offering a set of drop-dead gorgeous Hurricane RR forged wheels to anyone who wishes to avail them. The high-quality wheels measure 20 inches in the front and 21 inches at the back, ensuring that your AMG GT 4-door is riding on some of the best rims you can buy in the aftermarket world. Even better, a second rim model with a filigree multi-spoke design — it's called the Hurricane RS — is still baking in G-Power's in-house wheel oven. Once that set is out, you'll have another wheel option to choose from.

The rest of the exterior remains largely untouched, though it is worth pointing out, too, that interior upgrades are available based on a personalized basis. G-Power has enough interior dress-up options to make your head spin, but those options are largely available on an inquiry basis.

What's G-Power's engine upgrade program for the Mercedes-AMG GT 4-door?

G-Power's main objective in dabbling with the Mercedes-AMG GT 4-door is to give the high-performance saloon an engine upgrade that's fit for its stature. See, the AMG GT 4-door is already powered by a 4.0-liter twin-turbocharged V-8 engine that produces a naughty 577 horsepower and 590 pound-feet of torque. It's capable of accelerating from 0 to 60 mph in just 3.4 seconds, and it can hit a top speed of 193 mph. Those are delightful numbers, but they do not represent the peak of the saloon's potential. Not by a long shot.

That's where G-Power comes into the picture. The German tuner prepared an in-house tuned software program called GP-700. The plug-and-play kit zeroes in on the engine's ECU unit, unlocking more power in the process. The result is a more powerful twin-turbo V-8 engine that now produces an impressive 700 horsepower and 700 pound-feet of torque. Do the math, and you're looking at a power boost if 123 horsepower and 110 pound-feet of torque. It's important to point out that this kind of power already sits well into supercar territory. A 700-horsepower Mercedes-AMG GT 4-door can run with the bulls of the exotic car segment without breaking a sweat.

But the best part of it all? G-Power's engine upgrade offering for the AMG GT 4-door isn't done yet.

Wait, there are more engine upgrade programs?

Did you think G-Power's engine upgrade program was limited to just one software tune? The German tuner is renowned for launching multi-stage engine upgrade programs, and the new kit for the AMG GT 4-door is no different. There are three total stages in G-Power's program for the high-performance saloon.

The second-stage program involves a similar software procedure, albeit the slightly more potent GP-750 performance kit to go with in-house developed G-Power downpipes. That potent mix helps the twin-turbo V-8 engine produce a whopping 750 horsepower and 737 pound-feet of torque.

If these two programs aren't enough to tickle your funny bones, then, perhaps, G-Power's top-stage performance program will get you up on your feet. A pair of new turbochargers are included in the kit, and those are joined by new downpipes, sports air filters, a stainless steel exhaust system, and, last but certainly not least, G-Power's GP-800 performance software. All of these upgrades help turn the AMG GT 4-door into an 800-horsepower monster with the same 737 pound-feet of torque output being sent to the wheels.

G-Power didn't mention the kind of performance gains that the Mercedes-AMG GT 4-door stand to receive with these upgrades. We do know that, in stock form, the performance saloon's 3.4-second, 0-to-60-mph time, and 193-mph top speed are well established. Given the corresponding power gains, here's what we think the AMG GT 4 is capable of with these three G-Power engine upgrade kits. These figures are all estimates.

How much is all this madness going to cost me?

It's hard to say the total amount of the whole program because the final price will largely depend on the kind of interior upgrades you get. Fortunately, G-Power has announced pricing details for a lot of the items that make up the whole kit. The available set of 20- and 21-inch Hurricane RR wheels, for example, sells for €7,950 and €8,950, respectively. That converts to around $8,930 and $10,000, respectively.

As far as the software programs go, expect to pay a prince's ransom to avail of any of them. The GP-700, for example, is priced at €2,495 ($2,800). The mid-level GP-750 program, on the other hand, will set you back €2,995 ($3,300). Then there's the GP-800, which G-Power is selling for €3,595 ($4,040).

The two turbochargers that are included in the Stage 3 kit sells for €6,390 ($7,200) while the downpipes are priced at €5,360 ($6,000). The sports air filters only cost €238 ($270), but the stainless steel exhaust will set you back €4,850 ($5,450) on its own.

Suppose that you want the top-of-the-line package from G-Power, you're looking at a price north of $40,000 without anything happening to the interior of your AMG GT 4-door. Add some fancy leather and Alcantara in the cabin, and your total cost could approach $50,000 for the program alone to go with the $140,000 price tag of a brand new 2020 Mercedes-AMG GT 4-door.

Final Thoughts

This is G-Power we're talking about, so, of course, we have great things to say about the G-Power GP 63 Bi-Turbo. In true G-Power form, the German tuner was able to maximize the potential of the Mercedes-AMG GT 4-door without compromising the identity of the performance saloon. All the items included in the program are all carefully curated to fit together seamlessly. There's nothing excessive about any of the items; everything just fits into what the AMG GT 4-door is all about. With the G-Power kit, the AMG GT 4-door now has more power on tap, but it's a refined kind of power that should appeal to performance fiends and classy owners alike. Add another feather to your cap, G-Power. You did it again.