The 5.7 HEMI engine is a proven performer in the muscle car and truck world, delivering a solid 400 horsepower from the factory. But for enthusiasts chasing big power on a relatively affordable platform, adding a turbocharger is one of the most effective paths to 650+ horsepower. This expansion covers exactly what it takes to hit each power level, from a mild street boost setup to a fully built, high-boost combination. Whether you’re considering a single large turbo or a twin kit, the supporting mods, fuel system upgrades, and tuning details can make or break your build.

Stock 5.7 HEMI – What You’re Working With

The original 5.7-liter HEMI (third-generation) features a cast-iron block with aluminum heads, a 9.6:1 compression ratio in most applications, and a hemispherical combustion chamber. The factory intake, exhaust manifolds, and camshaft are designed for a broad torque curve and reliability, not extreme peak power. The stock bottom end includes cast pistons and powdered-metal connecting rods, which limit safe boost levels if you’re aiming for 600+ horsepower. In baseline trim, a 5.7 HEMI produces 395–410 net horsepower at the crank, depending on the model year and application.

Understanding these constraints is important because every power level above stock requires careful evaluation of the engine’s weak points. The HEMI’s strength lies in its robust block and head design, but the rotating assembly and fuel system are where most builders start upgrading.

Why Turbocharging Over Supercharging?

Both forced induction methods work, but turbocharging offers distinct advantages for the 5.7 HEMI. A turbo system’s boost curve is more controllable and can be tailored for peak efficiency at higher RPM, which is beneficial when chasing 650+ horsepower. Turbos also add less parasitic loss than a belt-driven supercharger, meaning more of the engine’s output goes to the wheels. Furthermore, with a well-sized single or twin turbo setup, you can maintain strong low-end torque while still achieving massive top-end gains. Many aftermarket kits (like those from Hellion, Hellion Power Systems, or On3 Performance) are designed specifically for the 5.7 HEMI, simplifying installation.

Power Level Tiers – From Stock to 650+ HP

Low Boost Street Setup: 450–500 Wheel Horsepower

With a conservative turbo kit running 5–7 psi of boost on a stock engine, you can expect roughly 450–500 wheel horsepower (approximately 520–580 at the crank). This level is achievable with a basic single turbo kit (60–62mm turbine) and stock fuel injectors if the fuel pump and pressure regulator are up to the task. The factory ECUs can be reflashed with a custom tune using HP Tuners or DiabloSport to add fuel and adjust timing. At this power level, the stock fuel pump and injectors are often at their limit, so an upgraded in-tank fuel pump and 65 lb/hr injectors are recommended for safety.

Driveability remains excellent. The engine still uses the stock camshaft, compression remains unchanged, and the drivetrain (transmission, differential) typically handles 500 wheel horsepower without immediate failure. This is a common entry point for street-driven HEMI vehicles like the Dodge Charger, Challenger, or Ram 1500.

Medium Boost Street/Strip Setup: 500–600 Wheel Horsepower

Boosting to 8–11 psi with a larger turbo (67–72mm) and upgraded fuel system pushes power into the 500–600 wheel range. At this point, you must upgrade the fuel injectors (80 lb/hr or higher) and the fuel pump (e.g., Walbro 450 or a dual-pump setup). An aftermarket intercooler is necessary to keep intake air temperatures in check. The stock camshaft is still usable, but swapping to a mild stage 1 or stage 2 HEMI cam can improve spool and power output while maintaining decent street manners.

Medium boost builds often require a transmission upgrade, especially for automatic-equipped cars (the 5-speed or 8-speed can handle 600 hp with a good tune, but the torque converter and clutch packs may weaken over time). Many builders also add a higher-capacity oil pan and consider upgrading the valve springs to prevent float at higher RPM.

High Boost Fully Built: 650+ Wheel Horsepower

Reaching 650+ wheel horsepower (roughly 750+ at the crank) demands a built bottom end. The stock cast pistons and powdered-metal rods can’t reliably handle 12–15 psi of boost, especially with pump gas. A forged rotating assembly—with forged pistons (often 9.0:1 compression or lower), forged H-beam or I-beam connecting rods, and a forged crankshaft (though the stock crank is usually strong enough at this level)—is essential. The cylinder heads benefit from upgraded valve springs, hardened pushrods, and possibly port work.

Fuel system upgrades become serious: 100+ lb/hr injectors, a dual pump setup with a surge tank, and possibly a boost-referenced fuel pressure regulator. An excellent intercooler (air-to-air or air-to-water) is mandatory to prevent detonation under sustained high boost. The turbo kit itself should be a larger single unit (76mm or bigger) or a twin turbo setup (50–55mm each) to flow enough air.

At this power level, the drivetrain must be upgraded: a built 8HP70 or 8HP90 transmission (for 8-speeds), a reinforced driveshaft, and a differential with stronger axles and a limited-slip unit. Many 650+ wheel horsepower HEMI builds also add a methanol injection or water-methanol system to cool the charge and raise the effective octane.

Essential Supporting Modifications – The Full List

Below are the critical components needed for each power level. The table is not included here, but the list below is organized by system:

  • Fuel System: Upgraded in-tank pump (Walbro 450 or 525), larger injectors (65–100 lb/hr), and a boost-referenced regulator. For 650+ HP, consider a dual pump or external pump with a surge tank.
  • Intercooler: At least a 3″ thick bar-and-plate core with efficient end tanks. Avoid small eBay cores for high boost.
  • Exhaust: Free-flowing downpipe and a 3″ or larger exhaust to reduce backpressure. Stock manifolds and cats are restrictive for high power.
  • Engine Internals: For 600+ wheel HP, forged pistons and rods. For 650+ wheel HP, also consider forged main studs and head studs to keep the bottom end sealed.
  • Valvetrain: Upgraded valve springs (e.g., PAC or Comp Cams), hardened pushrods, and possibly upgrading to a roller cam with better overlap for turbo efficiency.
  • Camshaft: A turbo-specific cam (lower duration, higher lift, wider lobe separation) helps spool and reduces reversion. Not mandatory for low boost but beneficial at medium and high levels.
  • Tuning: Custom ECU calibration via HP Tuners or DiabloSport. For advanced builds, a standalone ECU (Holley, Haltech) may be needed to fully control timing, fuel, and boost.
  • Cooling: Upgraded radiator and electric fans to handle the extra heat from boost. Oil cooler is recommended for track use.
  • Drivetrain: Built automatic transmission (e.g., upgraded valve body, torque converter, clutch packs), heavy-duty driveshaft, and upgraded axles for 650+ HP.

Turbo Selection – Single vs Twin, Size Matters

Choosing the right turbocharger depends on your power target and driving style. For 450–500 wheel HP, a single 62mm turbo (like a BorgWarner S362 or Garrett GT3582) offers fast spool and good top-end. For 500–600 wheel HP, step up to a 67–72mm turbo (e.g., Precision 6776 or Garrett GTX4294). For 650+ wheel HP, a single 76mm (e.g., BorgWarner SXE 476 or Garrett GTX4508) or twin turbos (e.g., 54mm each) provide the airflow required.

Twin turbo kits are common for V8 engines, allowing smaller turbos that spool quickly while still flowing enough for high horsepower. They also fit neatly on each exhaust bank. Single turbo kits simplify the plumbing but may lag more on a 5.7 HEMI that already has a mild cam. Many builders choose the single turbo route for simplicity and cost savings, then manage lag with a smaller exhaust housing and proper cam selection.

Always size the turbo for your intended boost pressure and RPM range. A turbo that’s too large will be laggy and hard to tune for street driving; too small will choke the top end and create excessive backpressure.

Tuning and Fuel Requirements

Fuel octane is a major factor in safe boost levels. On 93 octane pump gas, most 5.7 HEMI builds can safely run 10–11 psi with proper cooling and conservative timing. For 650+ wheel horsepower on pump gas, you’ll likely need a race gas mix, ethanol (E85), or water-methanol injection. E85 is popular because it provides a high effective octane and excellent knock resistance, but it requires a fuel system capable of flowing 30% more volume than gasoline.

Tuning must account for boost-advance tables, fuel enrichment, and knock control. The factory ECU can be modified for speed-density (map-based) tuning, which is preferred over MAF-based tuning when dealing with high boost. For extreme builds, a standalone ECU like the Holley Dominator or MoTeC offers full control over boost, fuel, and spark mapping, including closed-loop boost control and traction management.

Reliability Considerations

Pushing a stock 5.7 HEMI past 500 wheel horsepower puts stress on the head gaskets and ring lands. The cast pistons are the first weak link; under high boost, they can crack. The powdered-metal rods are also prone to bending if the engine detonates. For reliability at 650+ wheel horsepower, a forged rotating assembly and ARP head studs are non-negotiable. Also, consider adding a larger oil pan and an external oil cooler to manage heat buildup during sustained pulls.

Thermal management is critical. Turbochargers generate significant heat in the engine bay. Ceramic coating exhaust manifolds and downpipes, using heat wrap, and installing a turbo blanket help reduce under-hood temperatures. An air-to-air intercooler should be positioned in the front of the vehicle for maximum airflow; an air-to-water intercooler can be more compact but adds complexity with a pump and heat exchanger.

The transmission must be built to handle the torque. For the 8-speed ZF automatic, aftermarket torque converters and valve body upgrades are available. Manual transmissions (TR-6060, etc.) can hold 650 hp with a good clutch and possibly input shaft upgrades. The rear axle may also need attention; many Ram trucks and Charger/Challenger models use a 8.8″ or 9.25″ diff that can be reinforced with a limited-slip unit and stronger axles.

Real-World Build Example

A common high-boost build starts with a low-mileage 5.7 HEMI, a Hellion single turbo kit with a 76mm turbo, 100 lb/hr injectors, Walbro 525 pump, a custom cam from Comp Cams, forged pistons (9.0:1 compression), and a set of ARP head studs. Tuned on E85, this combination has been known to produce 720–750 wheel horsepower on a reliable tune. The owner upgrades to a built 8-speed transmission, LSD, and a 2.59:1 gear to maximize highway performance. With proper cooling and maintenance, such a car can be driven thousands of miles per year while hitting the drag strip on weekends.

Conclusion – Pick Your Target and Build Smart

The 5.7 HEMI turbo kit is a proven path to big power, but the supporting modifications and tuning determine the outcome. For a weekend warrior looking for 500 wheel horsepower, a basic kit with a pump upgrade and injectors is enough. For serious street/strip performance at 600+ wheel horsepower, forged internals and a full fuel system are required. And for the 650+ horsepower club, every component must be robust—from the bottom end to the cooling system. By following a tiered approach and understanding the weak points, you can build a HEMI that delivers exhilarating performance without sacrificing reliability.

For more information on specific turbo kits and components, check out Hellion’s HEMI turbo kits or read forum build logs on ChallengerTalk for real-world results.