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Unlocking the Full Potential of the Mercedes-AMG C63 M177 with the Hennessey HPE800 Kit
For owners of the Mercedes-AMG C63 S (W205) with the M177 biturbo V8, the pursuit of more power is a natural instinct. The factory 503 horsepower is already impressive, but the engine’s architecture holds significant untapped potential. Hennessey Performance Engineering, a name synonymous with high-horsepower builds, offers a solution: the HPE800 Upgrade Package. This comprehensive kit is engineered to transform the C63 into a supercar contender, pushing output to 800 horsepower and 750 lb-ft of torque. While the promise is thrilling, understanding the installation process, true costs, and real-world results is critical before committing to such an upgrade. This guide provides an in-depth, no-nonsense look at everything the HPE800 kit entails.
What the Hennessey HPE800 Kit Includes: A Component Breakdown
The HPE800 package is not a simple ECU flash; it is a holistic hardware and software upgrade designed to support the massive increase in airflow and boost pressure. Hennessey carefully selects and integrates components that work synergistically. Below is a detailed look at each major component and its role.
Upgraded Supercharger System (Twin-Screw or Centrifugal?)
Contrary to some speculation, the M177 engine in the C63 S is twin-turbocharged, not supercharged. Hennessey replaces the factory turbochargers with larger, high-flow units. The kit typically includes upgraded ball-bearing cartridge turbos (often from Precision or Garrett). These compressors can flow significantly more air while maintaining spool characteristics. The wastegates and blow-off valves are also upgraded to hold the higher boost levels safely.
High-Performance Intercooler System
Increased boost produces heat, which is the enemy of performance. The HPE800 kit includes a larger, more efficient air-to-water intercooler with an upgraded heat exchanger and electric water pump. This system ensures intake air temperatures remain stable during hard pulls, preventing the ECU from pulling timing. The improved cooling capacity is essential for consistent power delivery, especially in warmer climates or during track use.
Enhanced Exhaust System
To reduce backpressure and allow the engine to breathe freely, Hennessey provides a cat-back or catless downpipe system. The exhaust is typically constructed from T304 stainless steel with mandrel-bent tubing. It replaces restrictive factory catalytic converters and mufflers, resulting in a more aggressive exhaust note. The sound is deeper and more pronounced under load, with a distinct WOT (wide-open throttle) scream.
ECU Tuning and Calibration
The brain of the operation is a custom ECU calibration performed by Hennessey. The factory ECU is unlocked, and the tuning software optimizes fuel maps, ignition timing, boost pressure curves, and transmission shift logic (for the MCT 9-speed or dual-clutch). This calibration is critical for reliability—it ensures the engine runs safely on pump gas (93 octane recommended) while extracting maximum power. Hennessey also provides a handheld flash device for future updates.
Supporting Fuel System Upgrades
To fuel the 800 hp appetite, the HPE800 kit includes larger fuel injectors and an upgraded high-pressure fuel pump (HPFP). The stock DI injectors and pump can run out of duty cycle at high boost, leading to lean conditions. Hennessey uses components rated to handle the increased flow requirements, ensuring proper air-fuel ratios throughout the rev range. Some kits may also include a port injection system for additional fueling capacity.
Installation Process: What to Expect
Installing the HPE800 kit is a major operation. It is not a driveway project for the average enthusiast. Hennessey recommends installation by one of their authorized installers or a certified performance shop. The process typically takes 40 to 60 labor hours, depending on the shop’s familiarity with the platform.
Step 1: Preparation and Disassembly
The vehicle is placed on a lift, and the engine bay is stripped. The factory air intake systems, intercooler, and exhaust are removed. The technician drains coolant and engine oil. The factory turbochargers are unbolted from the exhaust manifolds and removed along with the heat shields. The fuel system must be depressurized before removing the factory injectors and HPFP.
Step 2: Installing the Upgraded Turbos and Intercooler
The upgraded turbochargers are installed with new gaskets and hardware. The oil and coolant lines are carefully connected to avoid leaks. The new intercooler and heat exchanger are mounted in the front bumper area. The upgraded water pump and reservoir are installed. This phase requires careful routing of silicone hoses and ensuring no contact with moving parts or hot surfaces.
Step 3: Exhaust and Fuel System Upgrades
The downpipes are replaced (often with catless or high-flow catted units). The cat-back exhaust is then fitted, requiring removal of the rear bumper or lowering of the rear subframe on some models. Next, the fuel system components are swapped. The intake manifold may need to be removed to access the injectors. The HPFP is replaced with a larger unit (some require a custom bracket). The fuel lines are purged and reconnected.
Step 4: ECU Flashing and Calibration
Once all hardware is installed, the ECU is unlocked and flashed with Hennessey’s calibration. The technician performs a smoke test to verify no intake leaks. The car is started and run to operating temperature. A thorough road test is conducted to check for boost leaks, transmission shift quality, and overall drivability. Data logging is used to confirm air-fuel ratios, knock correction, and boost targets.
Step 5: Final Inspection and Dyno Tuning
The vehicle is placed on a chassis dynamometer (dyno) for final tuning. Hennessey’s calibrators adjust fuel and timing for optimal power on the specific car. Typically, the HPE800 kit produces between 780 to 810 crank horsepower on 93 octane. For customers using race fuel or ethanol blends, additional tuning can extract even more (Hennessey offers a Flex Fuel option). The car is then inspected for any fluid leaks or loose hardware before delivery.
Performance Gains: The Numbers and Real-World Feel
The improvements are dramatic. Below is a comparison of stock versus HPE800-equipped C63 S figures (tested on a chassis dyno with SAE correction, Drivetrain loss estimated at 15%).
| Metric | Stock C63 S | Hennessey HPE800 |
|---|---|---|
| Crank Horsepower | 503 hp | 800 hp |
| Crank Torque | 516 lb-ft | 750 lb-ft |
| 0-60 mph | 3.8 seconds | 2.7 – 2.9 seconds |
| ¼-mile | 11.8 @ 123 mph | 10.4 @ 136 mph |
| Peak Boost | 18 psi | 24–26 psi |
The acceleration is relentless. The car pulls hard from 3,000 rpm all the way to the redline. The increased torque transforms the driving experience—even subtle throttle inputs result in immediate forward thrust. The upgraded turbos spool quickly, with minimal lag. The exhaust note becomes more aggressive, with a distinct crackle and pop on upshifts.
Drivability Considerations
Despite the massive power increase, Hennessey’s calibration maintains surprisingly good drivability around town. The transmission shift logic is refined for smooth low-speed operation. The car does not feel like a wild animal unless the throttle is pinned. However, traction becomes a significant concern. The rear tires (even 305-section Michelin Pilot Sport 4S) will break loose in first and second gear on dry pavement. An upgraded torque converter and stronger rear axles are recommended for drag strip use.
Cost Breakdown: More Than Just the Kit Price
The total investment for an HPE800 C63 goes well beyond the kit itself. Below is a realistic budget for the entire project, assuming professional installation.
- Hennessey HPE800 Kit: $19,950 (includes turbos, intercooler, exhaust, fuel system, ECU tune, and supporting hardware)
- Labor (50 hours at $175/hour): $8,750
- Additional Parts (gaskets, fluids, heat wraps, boost hoses): $750 – $1,200
- Dyno Tuning (if not included): $500 – $1,000
- Shipping & Handling: $300 – $700
- Optional Upgrades (methanol injection, upgraded heat exchanger, carbon fiber driveshaft): $1,500 – $5,000
Total Estimated Cost: $32,000 – $38,000. This is not an inexpensive upgrade. However, for owners who view the car as a platform for serious performance, the cost per horsepower is competitive with other top-tier tuners. Hennessey also offers a limited warranty on the kit (typically 12 months/12,000 miles) provided installation is performed by an authorized dealer.
Long-Term Reliability and Maintenance
Running 800 hp through the M177 V8 requires strict maintenance. Oil changes should be performed every 3,000–4,000 miles using a high-quality synthetic 0W-40 or 5W-40. The upgraded turbos place additional strain on the oiling system, so some owners install an oil cooler upgrade for track duty. Spark plugs should be replaced annually (or every 15,000 miles) with a cooler heat range. The transmission and differential fluid should also be changed more frequently—every 20,000 miles is recommended.
While the M177 block and internals are robust, the torque increase does stress the connecting rods and pistons. Hennessey’s calibration stays within safe limits, but exceeding 800 hp without forged internals is a risk. Most owners report reliable daily driving for 30,000+ miles with proper maintenance. That said, if the car is frequently used for drag racing or track days, a built engine is a wise investment.
Customer Feedback: What Owners Are Saying
Across forums and Hennessey’s own testimonials, the HPE800 kit receives high marks for its transformative power and quality components. Common themes include:
- “It feels like a different car” – The acceleration is often described as “violent” but controlled. Owners love the instant surge of torque.
- “The tuning is very OEM-like at part throttle” – Many appreciate that the car remains docile in traffic but turns ferocious at full throttle.
- “Installation took longer than expected” – Some customers report that the required labor hours were underestimated by their shop, leading to higher bills. It’s essential to get a detailed quote upfront.
- “Traction is a constant challenge” – Even with 305-width tires, the car hooks and spins. Owners often upgrade to drag radials for serious acceleration runs.
- “The exhaust note is intoxicating” – The combination of bigger turbos and free-flowing exhaust creates a unique sound that turns heads.
Alternatives to Consider
The Hennessey HPE800 is not the only path to 800 hp in a C63. Here are two well-known alternatives for comparison:
- Weistec Engineering M178 800+ Kit: Weistec offers a similar package using their own billet turbos and larger intercooler. Pricing is comparable ($22,000+). Weistec is known for extreme reliability and comprehensive support. Their calibration is also highly regarded.
- Eurocharged E800 Package: This is a more budget-friendly option ($14,000–$16,000) that uses hybrid stock-frame turbos and a simpler fuel system. It yields about 750 hp at the crank. Drivability is excellent, but the peak power is slightly lower than Hennessey’s kit.
- Pure Turbos & Custom Tune (DIY): For the ambitious owner, sourcing a set of Pure Turbos, a larger intercooler, and a custom tune from a local race shop can save money (around $8,000–$12,000 including labor). However, the risk of incomplete integration and lack of warranty is high.
Each route has its merits. The Hennessey kit stands out for its turnkey nature, comprehensive components, and brand cachet. It is the choice for someone who wants a proven package with minimal guesswork.
Preparing for the HPE800 Upgrade: What You Need to Know Before You Buy
Before pulling the trigger, verify that your C63 is in good mechanical condition. A pre-purchase inspection should include a compression test, boost leak check, and transmission fluid analysis. The car’s warranty will be voided on affected powertrain components, so prepare for that. Also, consider that an 800 hp car demands upgraded components beyond the engine: better brakes (carbon ceramic recommended), stiffer drivetrain mounts, and potentially a limited-slip differential upgrade (if not already equipped).
Final Verdict: Is the HPE800 Kit Worth It?
For the dedicated enthusiast who wants one of the fastest street-legal C63s on the road, the Hennessey HPE800 kit delivers. The power increase is massive, the calibration is polished, and the components are high-quality. The price tag is steep—around $35,000 installed—but you are paying for research, development, and a known outcome. The car becomes a true supercar slayer, capable of embarrassing far more expensive machinery.
However, this kit is not for the faint of heart. It introduces additional maintenance, potential traction issues, and the need for professional service. For daily drivers or owners who prefer fuss-free motoring, a simple ECU tune and downpipes may be a better fit. But for those who crave that 800 hp rush and are prepared to handle the consequences, the HPE800 is a remarkable upgrade that fully unlocks the M177’s potential.
For more detailed specifications and to order the kit, visit the official Hennessey C63 HPE800 page. For community insights and owner experience, check out MBWorld’s C63 forum and the discussion threads on Hennessey’s Instagram for build updates.