The sixth-generation Mercedes S-Class made its debut in 2013, and in the two full years that it’s been around, it has consistently sold well in the U.S. In fact, the S-Class turned in the second-most sales of any full-sized luxury sedan with 21,934 units sold in 2015, bested only by the Tesla Model S with 25,202 units. When you compare it with its two biggest rivals – the BMW 7 Series and the Audi A8 – the S-Class dominated both cars in terms of sales. The S-Class remains a popular choice for those in the market for a flagship sedan, so much so that Renntech has built a tuning program specifically tailored for the affluent clientele of the full-sized luxury Mercedes S550 (or S500 here in the U.S.).

It’s not a comprehensive kit, but it does include an engine tune that helps the Merc’s 4.7-liter twin-turbocharged V-8 engine increase its output to 530 horsepower and 606 pound-feet of torque. That’s a nice addition to the S550, but it’s far from the only one. Renntech also installed a carbon fiber aerodynamic component to go with a new set of wheels that are only limited to 25 sets. Talk about exclusivity, right?

All told, it’s a modest kit for a not-so-modest car. It may not entice those who prefer to get more aftermarket love for their S550s, but for those who prefer the subtle upgrades that don’t cut too much into the luxury sedan’s identity, this program from Renntech is a suitable option. It’s also affordable, or at least relatively so for those who obviously have the finances that allowed them to buy the S550 in the first place.

Continue after the jump to read the full story.

Exterior

Exterior modifications on the Mercedes S550 are light but they do cost the most of the entire kit. On the aerodynamic side, Renntech fitted the luxury sedan with a carbon fiber rear decklid spoiler that the tuner says will fit any S550 from 2014 and later. The spoiler serves the function of improving the flow of air in the back and reinforcing the downforce on the rear axles. The only other upgrade to the exterior is the new set of 21- and 22-inch Deep Monolite 10 Series alloy wheels that Renntech is limiting to just 25 sets.

Drivetrain

I meant it when I referred to the engine kit as a modest upgrade to the S550's 4.7-liter twin-turbocharged V-8 engine. In fact, Renntech’s work on the V-8 only consisted of an ECU upgrade. The method may be straight-forward, but the results are still impressive as the tuner was able to bring the output from the standard 455 horsepower and 516 pound-feet of torque to a tidier 530 ponies and 606 pound-feet of torque.

Performance numbers weren’t released, but with the standard S550 capable of sprinting from 0 to 62 mph in 4.8 seconds, the tuned-up version could cover that same distance in about 4.6 or 4.7 seconds. That’s enough of a difference to be considered noteworthy, especially for a car with this kind of size. On the flip side, top speed is likely to remain at 155 mph since Renntech didn’t mention anything about removing the engine’s Vmax limiter.

Pricing

Renntech's whole package costs a little over $15,000. That's an affordable price for people who already own a Mercedes S550. Breaking the price down reveals that the limited edition wheels account for the biggest chunk of the total price as it sells for $10,880. Meanwhile, the carbon fiber rear decklid spoiler sells for $1,680 while the ECU conversion is priced at $2,740. Do the math and that adds up to $15,300, excluding tax charges, shipping, and installation.

Competition

BMW Alpina B7 XDrive

Technically speaking, Alpina, as per the German Ministry of Transport, is considered an automobile manufacturer instead of an aftermarket tuner. But for the purposes of this comparison, let’s consider Alpina in both settings. That’s important because its BMW 7 Series-based B7 Drive is a good competitor to Renntech’s tuned-up Mercedes S550, or at least the previous version of it was. That car produced 540 horsepower and 538 pound-feet of torque and could hit 62 mph in 4.5 seconds, right around the numbers that the S550 is capable of. But the latest iteration of the B7 is a tad more powerful with 600 ponies on tap to go along with 590 pound-feet of torque. This allows the car to hit 0 to 60 mph in just 3.7 seconds and hit a top speed of 193 mph. Unless Renntech plans on removing the speed limiter on its S550 engine kit, Alpina’s B7 Drive is the better option.

Read our full review on the BMW Alpina B7 XDrive here.

Conclusion

Renntech isn’t going to turn the Mercedes S550 into a Mad Max-like warmonger of a luxury sedan, and that’s a good thing. See, the S550 is the type of car that doesn’t really need an aftermarket tuner. It already looks great. It has a well-appointed interior. And it has an engine that already pushes its output out to impressive levels. If the Mercedes luxury sedan did need an aftermarket program, it’s only because of the minor details that come with owning a legitimate full-sized flagship model. Renntech offers that kind of cherry on top of the proverbial sundae, which itself is good enough to give the S550 the tuning boost it needs to remain in tip-top condition.