Porsche 911 991 Turbo S Aerodynamic Downforce Tuning
The moment you cross 150 mph on a long straight, you feel the difference between a Turbo S that’s floating and one that’s truly planted.
The standard 991 Turbo S is already a remarkably stable car at speed. Porsche’s active aerodynamics system manages airflow in ways that most supercars can’t match. But for owners who track their cars or simply want more confidence at triple-digit speeds, there’s a world of tuning options beyond the factory setup. This guide breaks down what the stock system does, what the factory Aerokit adds, and what the aftermarket offers.
TL;DR
The Porsche 991 Turbo S uses an active aerodynamic system with a retractable rear wing and a multi-piece front spoiler. In standard form, it generates modest downforce at speed. Porsche Exclusive offers an official Aerokit that increases downforce by 37 pounds at the front and 40 pounds at the rear at 186 mph without increasing drag . Aftermarket companies like Moshammer and TechArt offer more aggressive packages designed for track use. The key trade-off is always the same: more downforce means more drag, which reduces top speed. Tuning your 991 Turbo S for downforce is about finding the right balance for how you actually drive the car.
Key Takeaways
- Standard 991 Turbo S generates modest downforce — approximately 20 kg front and 40 kg rear at 124 mph .
- Porsche Exclusive Aerokit adds significant downforce without increasing drag, preserving top speed .
- The active rear wing adjusts automatically based on speed, mode, and even whether the sunroof is open .
- Aftermarket options like Moshammer offer GT-RS-inspired packages for track-focused owners .
- More downforce always costs drag — you cannot have maximum stability and maximum top speed simultaneously.
- Always use performance features responsibly and follow local driving laws.
Understanding the Stock 991 Turbo S Aerodynamics
The Active System Explained
The 991 Turbo S was a pioneer for Porsche’s active aerodynamic systems. It uses multiple moving elements that adjust based on driving conditions.
At the front, there’s a three-piece spoiler that extends pneumatically. At the rear, the wing has multiple positions that change angle and height depending on speed and driving mode .
Real-world measurements from SportAuto’s wind tunnel testing showed the standard 991 Turbo S produced approximately 20 kg of downforce at the front axle and 40 kg at the rear at 124 mph (200 km/h) .
That’s modest by race car standards. Porsche prioritized efficiency and everyday usability over maximum grip.
How the System Adapts
The active system is smarter than most owners realize. Porsche engineers programmed it to adjust based on minute criteria, including whether a coupe’s sunroof is open or a convertible’s top is down. The rear wing has seven distinct positions to account for these variables .
In different driving modes, the aerodynamic setup changes significantly:
Normal mode: The rear wing stays retracted until 112 mph, when it extends to its first position. The front flaps open and close based on cooling needs .
Sport mode: The front spoiler extends at 75 mph, coinciding with the rear wing. This is the mode that achieves the claimed 205 mph top speed .
Sport Plus mode: Maximum downforce. The rear wing extends higher and tilts to its steepest angle. Top speed drops to 198 mph, but downforce increases to up to 375 pounds .
Wet mode: The front spoiler stays retracted while the rear wing extends, putting more force on the rear tires for stability in low-grip conditions .
This mode-dependent behavior is why simply adding a fixed wing can actually make the car slower or less stable in certain conditions. Porsche’s system balances front and rear downforce dynamically.
Porsche Exclusive Aerokit: The Factory Option
What It Includes
Porsche Exclusive developed an official Aerokit for the 991 Turbo and Turbo S. It consists of a new front spoiler panel with side fins and a completely redesigned rear decklid with a fixed trailing edge, side winglets, and a retractable rear wing with adjustable angle of attack .
The key achievement: Porsche engineers increased downforce while preserving the same coefficient of drag as the standard car. This means no top speed penalty .
Downforce Gains
The numbers are modest but meaningful. At 186 mph:
Speed setting: Front downforce increases by 37 pounds to 57 pounds. Rear downforce increases by 40 pounds to 331 pounds .
In metric terms at 300 km/h: Front increases by 17 kg to 26 kg. Rear increases by 18 kg to 150 kg .
The Aerokit is about high-speed stability, not track-day lap times. It makes the car feel more planted at autobahn speeds without changing its character.
Cost and Availability
The Porsche Exclusive Aerokit was offered at $6,950 when ordered with a new car, or $6,886 for retrofitting (excluding paint and installation) . It was available in body color or gloss black.
All vehicle warranty provisions remained in force when retrofitted at an authorized Porsche dealer .
Aftermarket Downforce Solutions
Moshammer Downforce RS and Evo RS
Moshammer, a Berlin-based specialist, offers a six-part aerodynamic package designed for 991 Turbo and Turbo S owners who use their cars on track .
The kit includes:
- Front spoiler (Evo I for aggressive look, Evo II with side wings for sharper appearance)
- Side skirts to minimize turbulence
- Rear spoiler extension for additional rear downforce
- Rear diffuser for reduced drag and improved traction
- Ram air scoops for intercooler efficiency
Moshammer’s approach treats the car as a single airflow problem rather than a collection of styling parts. The components attach at OEM mounting points and come with a TÜV parts certificate for documented legality in Germany .
The ram air scoops are a thoughtful addition. They improve intercooler efficiency, which keeps performance consistent during hard use — something a Turbo S needs on track.
TechArt Aerodynamic Programs
TechArt offers multiple aerodynamic packages for the 991 Turbo. Their bodykit is wind-tunnel tested and includes front and rear spoilers, side skirts, and an active rear spoiler that extends automatically above 120 km/h or manually via button .
TechArt’s design maintains the functionality of Porsche’s active aerodynamics. The front spoiler with active elements supports the factory system rather than replacing it .
For the 992 generation, TechArt’s aerokit maintains the variable front spoiler and adjustable rear wing in combination with new body parts, including a roof spoiler, carbon side air intakes, and a rear diffuser element .
TechArt’s offerings are more about individualization than pure performance. Their aero packages enhance appearance while maintaining daily usability.
Downforce Tuning Comparison
| Option | Downforce Gain (at 186 mph) | Drag Impact | Best For | Price Range |
|---|---|---|---|---|
| Stock 991 Turbo S | ~20 kg F / ~40 kg R (at 124 mph) | Baseline | Daily driving, occasional spirited runs | N/A |
| Porsche Exclusive Aerokit | +37 lbs F / +40 lbs R | No increase | High-speed stability, factory warranty | ~$6,950 |
| Moshammer Downforce RS | Not specified (GT-RS inspired) | Balanced with cooling | Track days, clubsport use | Custom quote |
| TechArt Aero Kit | Not specified (maintains active system) | Maintains factory CD | Individualization, street use | Varies by component |
The Physics You Cannot Ignore
Downforce vs. Drag
Every aerodynamic decision involves a trade-off. Downforce pushes the car onto the road, improving grip and stability. But creating downforce also creates drag, which limits top speed and increases fuel consumption.
Porsche’s genius with the 991 Turbo S is the active system that minimizes this trade-off. In Normal mode, the car is efficient. In Sport Plus, it’s planted. The driver chooses the balance .
Aftermarket fixed wings cannot replicate this. A big fixed rear wing adds downforce at all speeds, but it also adds drag at all speeds. For a car that spends most of its life on the street, this is often a bad trade.
The Front-Rear Balance Problem
Adding downforce to only one end of the car is dangerous. A rear wing without a matching front splitter creates aerodynamic imbalance — the rear grips more than the front, causing understeer at high speed.
This is why Porsche’s Aerokit includes both front and rear components . It is also why Moshammer’s package includes a front spoiler, side skirts, and diffuser alongside the rear spoiler extension .
Never add a rear wing to a 991 Turbo S without addressing front downforce.
FAQ
What is the standard downforce of a 991 Turbo S?
Independent testing measured approximately 20 kg front and 40 kg rear at 124 mph. Porsche’s active system adjusts these values based on speed and mode .
Does the Porsche Aerokit increase drag?
No. Porsche engineers specifically designed it to increase downforce while preserving the same coefficient of drag as the standard car .
Can I add a fixed rear wing to my 991 Turbo S?
You can, but it will create aerodynamic imbalance unless you also add front downforce. It will also increase drag and reduce top speed. Porsche’s active system is more sophisticated than any fixed wing .
How much does the Porsche Exclusive Aerokit cost?
Approximately $6,950 when ordered new, or $6,886 for retrofit (excluding paint and installation) .
Is the Moshammer kit legal for street use?
Yes, Moshammer supplies a TÜV parts certificate (§19.3), which documents the kit’s compliance with German regulations. Check local laws for your region .
Does downforce tuning void my warranty?
The Porsche Exclusive Aerokit does not void warranty when installed by an authorized dealer . Aftermarket parts may affect warranty coverage depending on your dealer and the specific issue.
What is the maximum downforce setting on a 991 Turbo S?
In Sport Plus mode, the active system generates up to 375 pounds of downforce, though this reduces top speed to 198 mph .
Final Thoughts
The 991 Turbo S is not a GT3 RS. It was never designed to be a track weapon with maximum downforce. It was designed to be the ultimate grand tourer — fast, comfortable, and stable at any speed.
That said, there is room to improve. The Porsche Exclusive Aerokit is the smart choice for owners who want more high-speed confidence without sacrificing daily usability or top speed. It is factory-engineered, warranty-friendly, and proven in the wind tunnel .
For track-focused owners, aftermarket options like Moshammer offer more aggressive solutions. But understand the trade-offs. More downforce means more drag. More drag means less efficiency. The 991 Turbo S’s active system exists precisely to avoid these compromises.
The best aerodynamic tuning is not the most aggressive. It is the one that matches how you actually drive the car.
Have you added aerodynamic upgrades to your 991 Turbo S? What changes did you notice? Share your experience in the comments.
References:
- Car and Driver — Porsche Offers Aerokit for 911 Turbo and Turbo S
- Car and Driver — Adjustable Aerodynamics on Porsche 911 Turbo S Now Include Air-Brake Function
- Porsche Newsroom — New Aerokit for the 911 Turbo
- Bulletproof Automotive — Moshammer Downforce RS Aero Kit 991.1
- Bulletproof Automotive — Moshammer Downforce Evo RS 991.2 Turbo
