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The Mercedes-Benz C63 AMG, powered by the naturally aspirated M156 V8, remains a benchmark for German muscle sedans. While the engine's 6.2-liter displacement delivers visceral torque and a legendary soundtrack, many owners eventually seek more power. A supercharger is the most direct path to significant gains, and two of the most reputable systems come from Kenne Bell and RENNtech. Both transform the C63 into a bona fide supercar slayer, but they come at very different costs—not just in dollars, but in complexity and long-term ownership considerations. This comprehensive breakdown will help you budget for your build, understand what each kit includes, and weigh the trade-offs before making a serious investment.
Understanding the M156 Platform and Supercharging
The M156 is a robust, hand-built engine designed for high-RPM performance. Its forged steel crankshaft, powdered-metal connecting rods, and aluminum block can handle substantial power increases—provided the supporting systems are upgraded. Supercharging is not a simple bolt-on; it demands attention to fuel delivery, cooling, and engine management. Both Kenne Bell and RENNtech have engineered kits that address these needs, but their approaches and pricing reflect different philosophies.
The Case for Forced Induction on the M156
Without a turbocharger, the M156 relies on displacement and cam timing to make its rated 451 horsepower (or 481 in the Performance Package). A supercharger mechanically driven by the engine's crankshaft provides immediate boost, dramatically increasing air density into the cylinders. The result is a broad torque plateau that shaves seconds off quarter-mile times and transforms highway passing ability. However, the increased cylinder pressure and heat require careful management to avoid detonation or mechanical failure.
Kenne Bell Supercharger System: High Boost, High Value
Kenne Bell is synonymous with twin-screw superchargers. Their system for the C63 uses a 2.8L or 3.6L twin-screw rotor pack that compresses air efficiently, producing boost from idle to redline. The kit includes a custom intake manifold, intercooler cores, fuel injectors, and a calibration tool. It is designed for owners who want aggressive power delivery—the trademark "Kenne Bell whine" is unmistakable.
Cost Breakdown
- Supercharger Kit: $6,500–$7,200 (depending on rotor size and included accessories)
- Installation Labor: $1,200–$1,800 (varies by shop; expect higher for a complete teardown)
- Tuning and Calibration: $800–$1,200 (custom dyno tune recommended)
- Miscellaneous Parts: $300–$600 (hoses, clamps, upgraded belts, coolant)
- Supporting Mods (if not already installed): $1,500–$3,000 (larger heat exchanger, upgraded intercooler pump, colder spark plugs, fuel system upgrades)
- Total Estimated Range: $10,300–$13,800
The base kit price is attractive, but many cars require additional cooling capacity. The M156 runs hot from the factory; adding a supercharger amplifies that. A larger heat exchanger and a high-flow intercooler pump are strongly advised to maintain consistent power in hot weather. Without them, the engine management system will pull timing to protect the engine, negating the power gains.
Performance Expectations
On a healthy M156, a Kenne Bell kit can produce between 600 and 650 wheel horsepower on pump gas, with torque peaking near 600 lb-ft. With a conservative tune and proper cooling, the system is reliable for street use. Kenne Bell's twin-screw design provides swift throttle response—boost comes on immediately, making the car feel ferocious from any RPM. However, this instant torque can stress driveline components, particularly the 7-speed automatic transmission and the limited-slip differential, which may need reinforcement at higher power levels.
RENNtech Supercharger System: Refined Performance and Reliability
RENNtech has a storied history with Mercedes-Benz performance. Their C63 supercharger kit is a complete, turnkey solution that prioritizes reliability and drivability. It features a liquid-to-air intercooled manifold, a high-output Eaton TVS 2300 supercharger, upgraded injectors, a custom fuel pump module, and a reflashed ECU. RENNtech's calibration is legendary for its smoothness and safety, often producing slightly lower peak numbers but exceptional consistency.
Cost Breakdown
- Supercharger Kit: $7,000–$8,000 (includes tuning and calibration in the price)
- Installation Labor: $1,500–$2,500 (RENNtech recommends their own installation or a certified shop)
- Tuning and Calibration: Included in the kit price (but a follow-up dyno tune may be $500–$800 additional)
- Miscellaneous Parts: $400–$700 (charge pipe clamps, vacuum line kit, coolant)
- Supporting Mods (recommended): $2,000–$4,000 (upgraded heat exchanger, auxiliary water-methanol injection, reinforced differential)
- Total Estimated Range: $10,900–$15,200
RENNtech's kit is more expensive upfront, but it includes a comprehensive calibration that many owners find worry-free. The kit is designed to integrate with the factory cooling systems, though RENNtech still recommends an upgraded heat exchanger for sustained track use. The Eaton TVS supercharger is quieter than the Kenne Bell twin-screw, producing a subtle whine rather than a loud wail, which some owners prefer for daily driving.
Performance Expectations
RENNtech claims 620–670 horsepower at the crank (approximately 540–580 wheel horsepower) on 93 octane. The torque curve is broader than the Kenne Bell, with less peak but more area under the curve. This translates to a car that pulls seamlessly from 2,000 rpm to redline without a sudden surge. Many owners report that the car feels OEM+, with linear, predictable power. Reliability is a strong selling point; RENNtech's reputation for longevity on the M156 is well documented, with many supercharged examples exceeding 100,000 miles without major issues when maintained properly.
Installation Complexity and Labor Costs
Both kits require significant disassembly: removal of the intake manifold, fuel rails, and stock airbox. The supercharger unit itself bolts onto the engine, but the intercooler system, belt routing, and fuel system modifications add hours. Expect a shop to charge 12–18 hours for either installation. A skilled technician familiar with M156 supercharger installations can complete the job in 14 hours, but a shop learning the process may take 20+ hours, increasing costs.
Additional Labor Considerations
- Accessories: Installing an upgraded heat exchanger, auxiliary fans, and a water-methanol injection system adds 4–8 hours.
- Transmission Tuning: The 7-speed automatic (MCT or traditional) may need a transmission control unit (TCU) tune to handle increased torque. This is often performed by the same tuner and can add $500–$700.
- Differential Service: Consider upgrading the differential bearings and adding an auxiliary cooler. Many high-mileage M156 diffs develop bearing whine under increased load. Rebuild cost can be $1,500–$3,000.
Tuning: The Critical Differentiator
The Kenne Bell kit typically includes a handheld programmer with a base tune, but most owners invest in a custom dyno tune to optimize for their specific fuel and climate. A bad tune on the M156 can lead to catastrophic engine failure—broken piston rings, cracked exhaust valves, and even piston failure. RENNtech's included calibration is meticulously developed on their own test mule, reducing the risk. However, if you plan to run ethanol blends (E30 or E85), a custom tune from a specialist like Eurocharged or AMG-HP is essential regardless of which kit you choose.
Fuel System Upgrades
Both kits require upgraded fuel injectors (typically 1,000–1,200cc) and a higher-flow fuel pump. The M156's direct injection system adds complexity—some supercharger kits use port injection alongside the direct injection to provide additional fueling. RENNtech's kit addresses this with an auxiliary port injection system, while Kenne Bell relies on larger direct injectors and a boost-a-pump. Make sure you understand the fueling approach before purchasing; port injection adds cost but simplifies ethanol use.
Supporting Modifications You Can't Skip
Cooling is king. The M156's factory cooling system is already borderline for stock power. Adding a supercharger without upgrading the radiator, heat exchanger, and intercooler pump is asking for heat soak. On a hot day, a stock-cooled supercharged C63 may see intake air temperatures over 150°F, causing the ECU to pull timing and reduce power to 500 wheel horsepower or less. A high-quality heat exchanger (like AFE Power or CSF) and a Bosch or Stewart intercooler pump are must-haves.
Exhaust system upgrade is strongly recommended. The stock manifolds are restrictive. Long-tube headers (from companies like Kooks or MHP) can add 30–50 wheel horsepower and reduce exhaust gas temperatures, helping the engine survive high boost. Budget $2,800–$4,000 for headers and installation.
Driveline reinforcement is often overlooked. The 7-speed automatic can handle 650 wheel horsepower with a good tune, but the clutches may slip after repeated hard launches. A transmission cooler is essential. The rear differential's output shaft bearings are a known weak point; consider a differential upgrade from Wavetrac or a rebuild with stronger bearings.
Comparing Ownership Costs
| Category | Kenne Bell | RENNtech |
|---|---|---|
| Initial hardware + install | $8,800–$9,800 | $10,800–$12,500 |
| Recommended supporting mods | $2,500–$5,000 | $2,500–$5,000 |
| Custom tune (if not included) | $800–$1,200 | $0–$800 |
| Yearly maintenance increase | $400–$800 (oil changes, spark plugs, belt service) | $400–$800 |
| Long-term reliability perception | Good, but more aggressive boost curve may cause earlier driveline wear | Excellent; proven with multiple street-driven high-mileage examples |
Choosing the Right Kit for Your Goals
Track vs. Street Use
If you primarily drag race or roll race, the Kenne Bell's peak horsepower advantage and instant boost may appeal to you. The loud whine is also a badge of honor among enthusiasts. However, if you value daily drivability, long road trips, and a seamless power band that doesn't invite a transmission failure, the RENNtech kit is the safer bet. Many owners report that the RENNtech car feels like a factory supercharged Mercedes, while the Kenne Bell car feels like a wild hot rod.
Budget Constraints
If your budget is tight around $10,000 total, the Kenne Bell kit leaves less room for supporting mods. You may need to skip the heat exchanger upgrade initially, but that risks heat soak. A better approach is to save until you can afford the full package. The RENNtech kit, while more expensive, includes the tuning and often a more complete cooling package, reducing the surprise costs.
Resale Value
Supercharged C63s are rare and desirable. A properly installed, low-mileage example with a RENNtech kit may command a higher resale price because of the brand's reputation and the clean installation. Kenne Bell cars can also sell well, but buyers often worry about the tune and maintenance history. Keep all receipts and documentation of the dyno tune and service work.
Maintenance After Supercharger Installation
Oil changes should be performed every 3,000–4,000 miles with a high-quality 5W-40 synthetic. Spark plugs need replacement every 15,000–20,000 miles; use colder heat range plugs (NGK 7 or 8) to prevent pre-ignition. Inspect the supercharger belt at every oil change; a broken belt can lead to boost loss and possible engine damage from debris. Change the supercharger oil every 50,000 miles (Kenne Bell recommends their proprietary oil). The water-methanol injection system, if installed, requires monthly refills and nozzle inspection.
Consider installing an oil catch can to reduce carbon buildup on the direct injection valves. The M156 is prone to intake valve deposits even in stock form; supercharging accelerates it. A catch can is a $200–$400 investment that can save thousands in future cleaning.
Final Thoughts on the $10,000+ Decision
Installing a supercharger on a C63 AMG is not a weekend project for most enthusiasts. It's a serious engineering undertaking that requires careful planning, a significant budget, and a willingness to accept increased maintenance. Both Kenne Bell and RENNtech deliver extraordinary performance, but they cater to different priorities. Kenne Bell offers more peak horsepower for less initial cost, but demands more supporting upgrades. RENNtech provides a complete, proven package with exemplary calibration and reliability, at a higher entry price.
Whichever route you choose, work with a shop that has experience on the M156. The difference between a successful build and a nightmare lies in the installation and tuning. The reward—a 600+ wheel horsepower naturally aspirated V8 with a supercharger screaming under the hood—is an experience you'll not soon forget.
For further research, consult the specialists: Kenne Bell's official site for kit details, RENNtech's C63 page for their system, and the MBWorld C63 AMG forum for real owner experiences. Also consult Eurocharged for standalone tuning options if you plan to go beyond the base calibrations.