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Unlocking 800 Horsepower: The Hennessey HPE800 for Jeep Grand Cherokee SRT
The Jeep Grand Cherokee SRT is already a formidable performance SUV, packing a 6.4-liter HEMI V8 that delivers 475 horsepower from the factory. For enthusiasts who crave more, Hennessey Performance Engineering offers a well-known upgrade path: the HPE800 package. This transformation elevates the SRT into a true super-SUV, pushing output to a staggering 800 horsepower. More than just a number, the HPE800 represents a comprehensive engineering package that redefines acceleration, throttle response, and overall driving dynamics. Whether you’re looking to dominate at the track or simply enjoy an unrivaled street presence, this upgrade is designed to deliver.
What the HPE800 Upgrade Entails
The HPE800 is not a single modification; it is a carefully engineered system of complementary upgrades. Each component is selected and tuned to work together, ensuring reliability alongside the massive power increase. The core of the package is a high-flow supercharger system, but it is supported by custom engine calibration, upgraded fuel delivery, and exhaust improvements. Hennessey has developed this package specifically for the 6.4-liter HEMI V8 in the Grand Cherokee SRT, meaning it bolts on without major fabrication while maintaining daily drivability.
Core Components of the Package
- High-Flow Supercharger System: A roots-type or twin-screw supercharger (depending on production version) that provides immediate boost from low RPMs. The unit includes a custom intake manifold and oversized intercooler to keep intake air temperatures in check.
- Custom ECU Calibration: Hennessey engineers remap the engine control unit to optimize fuel delivery, ignition timing, and boost pressure. This tuning is critical for achieving the 800 hp target while maintaining safe air-fuel ratios.
- High-Flow Exhaust System: To reduce backpressure and improve exhaust flow, the package includes a stainless steel cat-back exhaust with larger pipes and free-flowing mufflers. The result is a deeper, more aggressive exhaust note.
- Upgraded Fuel System: The added power requires more fuel. The HPE800 includes higher-flow injectors and an upgraded fuel pump to deliver the necessary volume under boost.
Performance Specifications That Matter
The numbers tell a compelling story. The Hennessey HPE800 Grand Cherokee SRT delivers performance that rivals exotics while offering SUV practicality.
| Metric | Stock Grand Cherokee SRT | Hennessey HPE800 |
|---|---|---|
| Horsepower (crank) | 475 hp | 800 hp |
| Torque (crank) | 470 lb-ft | 850 lb-ft |
| 0–60 mph | 4.3 seconds | Under 3.5 seconds |
| ¼-mile | 12.4 seconds | Under 11.0 seconds |
| Top Speed | 160 mph (limited) | 180 mph (estimated) |
These figures are achievable with proper tires and traction. Many owners report 0–60 mph times in the low 3-second range on sticky tires. The torque curve remains broad, making the SUV feel muscular from idle to redline.
Driving Experience: From Daily Driver to Track Weapon
While the numbers are impressive, the real-world driving character is what sets the HPE800 apart. The supercharger provides linear, immediate boost—no lag to speak of. Around town, the SRT remains docile; the exhaust is manageable at low speeds, and the automatic transmission shifts smoothly. But when you push the throttle, the surge of power is addictive. The chassis and suspension can handle the extra grunt, though upgraded brakes are highly recommended for repeated hard stops.
Hennessey also offers optional suspension upgrades to improve handling. The standard SRT adaptive dampers can be recalibrated, or owners can fit lowering springs for a more aggressive stance. For track use, the HPE800 requires high-performance summer tires; the stock all-seasons simply cannot put the power down.
Sound and Character
The supercharger whine is audible but not intrusive. Combined with the HPE exhaust, the soundtrack is a mix of mechanical whine and deep V8 rumble. It’s an experience that turns heads without being offensive to neighbors.
Installation and Build Process
Hennessey recommends that the HPE800 be installed by their trained technicians in Texas or by an authorized installer. The process is not a weekend DIY job; it involves disassembly of the intake system, fuel system modifications, and precise ECU tuning. Total installation time is typically 3–5 days, depending on the shop schedule and vehicle condition.
The package includes a detailed dyno sheet before and after installation, verifying the power figures. Hennessey also provides a limited warranty (typically 2 years/24,000 miles) on their parts and installation, though the factory powertrain warranty may be voided. Owners should check with their dealer and insurance provider before proceeding.
Cost Considerations
The HPE800 upgrade is a significant investment. The base package (supercharger, tuning, exhaust, fuel system) starts around $22,000. Installation labor adds $2,000–$4,000 depending on the shop. Many owners also opt for upgraded heat exchangers, a more aggressive camshaft, or forged internals for higher durability, which pushes the total above $30,000.
Is it worth it? Considering that a new Grand Cherokee SRT starts around $85,000, the total investment of $110,000–$120,000 places it in the realm of used supercars. However, the SUV remains practical for daily use, and the performance gain is undeniable.
Reliability and Maintenance
Hennessey designs the HPE800 to be reliable when driven responsibly. However, with 800 hp, the drivetrain is under more stress. The stock 8-speed automatic transmission is robust, but hard launches can cause heat build-up. Hennessey recommends transmission cooler upgrades for frequent track use. Regular maintenance—oil changes every 5,000 miles with full synthetic, spark plug changes every 30,000 miles, and supercharger belt inspections—is essential.
Owners should also monitor fuel quality. The HPE800 requires premium pump gas (93 octane recommended). Using lower octane can result in knock retard and reduced power.
Comparison to Other Hennessey Upgrades
Hennessey offers several stages for the Grand Cherokee SRT. The HPE700 (700 hp) is a more modest step, while the HPE850 (850 hp) and HPE1000 (1,000 hp) push further. The HPE800 sits in the sweet spot: it delivers a massive power increase without requiring internal engine modification (forged pistons, rods) that the HPE1000 needs. For most owners, the HPE800 is the ideal balance of power, reliability, and cost.
Resale Value
A Hennessey conversion can increase resale value, but it depends on the buyer. Enthusiasts will pay a premium for a documented, professionally installed HPE800. However, some buyers may be hesitant due to warranty concerns. If you plan to sell, keep all paperwork, dyno sheets, and service records. The resale uplift is typically $10,000–$15,000 over a comparable stock SRT, provided the car is well-maintained.
Final Thoughts
The Hennessey HPE800 upgrade transforms the Grand Cherokee SRT into an absolute monster. It combines the practicality of a family SUV with the performance of a supercar. The engineering is thorough, the power delivery is addictive, and the package is backed by a reputable company. For those who want to leave nearly everything else in the rearview mirror, the HPE800 is a proven path.
Before pulling the trigger, consider your driving style, budget for maintenance, and warranty implications. If you’re ready for 800 hp, Hennessey’s experience with the HEMI V8 makes the HPE800 a compelling choice.