Turbo Size and Supporting Mods for 5.7 Hemi: from 500 Hp to 700+ Hp

Introduction to Turbocharging the 5.7 Hemi for 500–700+ Horsepower

The 5.7-liter Hemi V8 is a legendary engine that powers everything from Ram trucks to Dodge Chargers and Challengers. While it’s no slouch in stock form, enthusiasts seeking serious power gains often turn to forced induction. A properly designed turbo system can take the 5.7 Hemi from a respectable 350–400 wheel horsepower into the 500–700+ range, transforming the driving experience. However, slapping on a large turbo without carefully matching it to the engine’s flow characteristics and supporting modifications is a recipe for disappointment and mechanical failure.

This guide provides a detailed breakdown of turbo sizing, supporting mods, and the key decisions needed to build a reliable 500–700+ horsepower 5.7 Hemi. We cover everything from compressor maps and turbine AR ratios to fueling, cooling, and internal engine upgrades. Whether you are planning a single turbo street build or a twin-turbo track monster, the principles remain the same.

Understanding Turbo Sizing for the 5.7 Hemi

Turbo selection is a balance between airflow capacity, response, and the engine’s volumetric efficiency at a given boost level. For the 5.7 Hemi, displacement is 5.7 liters (345 cubic inches). The key objective is to move enough air to support the target horsepower while keeping the turbo operating in its peak efficiency island.

Key Turbo Parameters

Compressor Wheel Diameter (Inducer/Exducer): Larger compressors flow more air, but require more turbine energy to spool. For 500–700 hp, inducer diameters of 60–80 mm are common.
Turbine Wheel and Housing A/R Ratio: A/R (Area/Radius) affects exhaust gas velocity. A lower A/R (0.70–0.85) improves spool but can choke high flow. A higher A/R (0.90–1.10) flows more at top end but adds lag. Optimal A/R depends on cam timing, exhaust design, and intended boost.
Compressor Trim: Trim is the ratio of inducer to exducer area. Higher trim means more flow but may sacrifice surge margin. Street builds generally use 60–70 trim compressors.
Boost Pressure Target: For 700+ hp, boost levels of 12–18 psi are typical with race gas or E85. Pump gas builds may target 8–12 psi with proper intercooling and knock control.

Recommended Turbo Sizes for 5.7 Hemi

Horsepower Target	Recommended Turbo Size	Notes
500–600 hp	Single 62–67mm, or twin 55–58mm	Good response, modest boost. Stock internals possible with safe tune.
600–700 hp	Single 72–76mm, or twin 60–62mm	Requires upgraded fuel system and intercooler. Forged pistons recommended.
700–800+ hp	Single 80–88mm, or twin 64–67mm	Race fuel or E85 strongly advised. Full forged rotating assembly needed.

Real-world example: A 76mm Precision Gen2 turbo on a 5.7 Hemi with 13–15 psi and good camshaft has repeatedly produced 650–700 wheel horsepower on E85. For street use, a 72mm unit offers quicker spool while still supporting over 600 hp. For dedicated race applications, consider an 88mm unit, but expect turbo lag below 4000 rpm.

Single vs Twin Turbo Configuration

Both single and twin turbo setups have distinct trade-offs for the 5.7 Hemi.

Single Turbo: Simpler packaging, fewer parts, lower cost. One large turbo can match the flow of two smaller units. Lag is often more pronounced but can be mitigated with modern billet wheels and anti-surge housings. Exhaust plumbing is easier with a single crossover pipe.
Twin Turbo: Improves spool by using two smaller turbos that reach boost sooner. Allows shorter exhaust runners (equal length). Twice the hardware means more potential leak points and higher cost. Often chosen for high-horsepower street builds seeking instant throttle response.

For most 5.7 Hemi owners targeting 600–700 hp, a single 76mm turbo is the most cost-effective and proven route. Twin 62mm setups can deliver slightly better low-end response but at a 30–40% price premium.

Supporting Modifications for Turbocharged 5.7 Hemi

Making reliable power requires more than just bolting on a turbo. The engine, drivetrain, fuel system, and cooling must all be up to the task. Below are the critical supporting modifications organized by system.

Fuel System

At 500+ wheel horsepower, the factory fuel pump and injectors will be overrun. For 600–700 hp, you need:

Fuel Pump: An in-tank 340–450 LPH pump (e.g., Walbro 525 or Aeromotive 340) for pump gas or a brushless pump for E85. Must support 60–80 psi at high flow.
Fuel Injectors: 80–105 lb/hr injectors (high impedance) are common for 600–700 hp on gasoline. For E85, increase injector size by 30–40% (100–150 lb/hr). Use injector dynamics or Bosch EV14 style.
Fuel Pressure Regulator: Boost-referenced return-style system with a quality regulator to maintain consistent differential across injectors.
Fuel Lines: -6AN or -8AN feed, -6AN return. E85 requires specific ethanol-rated materials.

Intercooler System

Lowering intake air temperature is critical for knock prevention and power consistency. An air-to-air intercooler is typical for street builds.

Core Size: At least 3.5–4.0 inches thick, 24–28 inches wide, with 2.5–3.0 inch inlet/outlet. A bar-and-plate design offers better heat rejection than tube-and-fin.
Charge Piping: 2.5–3.0 inch aluminum tubing with smooth bends. Silicone couplers with T-bolt clamps.
Blow-Off Valve (BOV): A 50mm or larger bypass valve protects the compressor wheel and prevents surge. Plumbed to atmosphere or recirculated per tuner preference.
For those seeking maximum cooling, consider water-to-air intercoolers with an ice tank for drag racing.

Exhaust System

Flow restriction kills turbo efficiency. After the turbo, the exhaust must be free-flowing:

Downpipe: 3.0–3.5 inch stainless steel mandrel-bent from turbine outlet. A v-band connection simplifies removal.
Muffler: A straight-through borla or MagnaFlow type to minimize backpressure. Avoid chambered mufflers.
Upstream Exhaust: For turbo applications, many use “turbo manifolds” with short, equal-length runners to improve spool. Avoid restrictive log manifolds.

Cooling System

Boost generates huge heat. The 5.7 Hemi has a known tendency for high cylinder head temperatures under sustained load. Upgrades include:

Radiator: All-aluminum 2–3 row core with higher capacity. For 700+ hp, consider a 32-inch wide radiator from a performance supplier.
Electric Fans: Dual 14–16 inch high-CFM fans (Spal or Derale) with a shroud. A 200-amp alternator may be needed to support the current draw.
Oil Cooler: A 19-row or larger oil cooler with thermostat. Forced induction increases oil temps dramatically.
Water Pump: An electric water pump (e.g., Meziere) provides constant coolant flow regardless of rpm and reduces parasitic loss.

Engine Management and Tuning

Proper calibration is non-negotiable. The 5.7 Hemi uses a variety of ECUs depending on year (NGC, SGW, etc.). Options:

Standalone ECU: Options like Holley EFI, FuelTech, or MoTeC for full control. Requires rewiring but offers unlimited tuning flexibility.
Piggyback or Flash Tuning: HP Tuners or DiabloSport with a custom tune is simpler for street cars. Works with stock ECU for incremental gains.
Boost Controller: A manual or electronic boost controller (e.g., Turbosmart e-Boost 2) allows on-the-fly adjustment. Gateway for safe tuning.
Wideband O2 Sensor: Essential for monitoring air-fuel ratio during tuning. Use a sensor placed in the downpipe.

Internal Engine Upgrades for 700+ Horsepower

Stock 5.7 Hemi internals are cast pistons and powder-metal connecting rods. They can handle up to about 500–550 wheel horsepower with a conservative tune. Beyond that, catastrophic failure is likely. For a reliable 700+ hp build, upgrade the following:

Pistons

Forged pistons (e.g., Diamond, Wiseco, JE) with a lower compression ratio (9.0–9.5:1) are standard. For turbocharged high boost, a dish design reduces static compression and increases clearance for valve relief. Choose 2618 alloy for highest strength, or 4032 for less expansion in street applications.

Connecting Rods

Stock powdered-metal rods bend under high cylinder pressures. Upgrade to 4340 forged H-beam rods (e.g., K1 Technologies, Callies). Pay attention to rod length: the standard 5.7 Hemi rod is 6.200 inches, but many aftermarket rods are 6.200 or 6.125 depending on piston choice.

Camshaft and Valvetrain

A turbo camshaft differs from naturally aspirated. You want reduced overlap to avoid push-through of boost during overlap. Typical turbo cam specs for 5.7 Hemi:

Duration: 220–236 degrees at 0.050 inch lift on intake, 224–240 on exhaust. More exhaust duration helps spool the turbo.
Lobe Separation Angle (LSA): 114–116 degrees is common for turbos to minimize overlap and improve low vacuum.
Valve Springs: Upgrade to dual springs with 140–160 lb seat pressure to control valve float at 6500+ rpm.
Pushrods and Rockers: Stock rockers can handle moderate boost, but adjustable rockers or shaft-mounted systems are better at high rpm.

Head Studs

Factory head bolts can lift under high cylinder pressure, leading to blown head gaskets. Install ARP 2000 or L19 head studs with a quality MLS gasket (e.g., Fel-Pro PermaTorque).

Rotating Assembly Balance

Any internal upgrade must be balanced as a set. Failure to do so causes bearing fatigue and potential rod cap separation. Use a harmonic damper (ATI Super Damper) to control crank torsional vibration at high power levels.

Drivetrain Considerations

Making 600–700 hp is useless if the transmission or rear end cannot hold it. For the 5.7 Hemi in Challenger/Charger/Ram applications, the following are critical:

Automatic Transmission: The 8HP70 (8-speed) can handle around 550–600 lb-ft stock. For sustained 700+ hp, upgrade valve body, clutches, and torque converter (e.g., PTC or high stall). The 8HP90 used in Hellcats is a direct swap for higher capacity.
Manual Transmission: Tremec TR-6060 (or T-56 Magnum) with a robust clutch (McLeod RXT or Centerforce DYAD) is necessary.
Differential: Upgrade to a limited-slip or TrueTrac with 31- or 35-spline axles. The factory open differential will struggle with traction.

Fuel and Tuning Considerations

The use of E85 (ethanol) is highly recommended for high-boost 5.7 Hemi builds. E85’s high octane (105+ RON) and cooling effect reduce knock tendency, allowing more timing and boost. However, E85 consumes roughly 30% more fuel volume, so fuel system must be sized accordingly.

If staying on pump gas (93 octane), keep boost under 12 psi and use water/methanol injection as a safety net. Intercooler efficiency is even more critical.

Tuning Tips: Start conservative, add timing in small increments while monitoring knock sensors. Use extra injector duty cycle safety limits. A dyno session with a reputable tuner experienced in Hemi turbo builds is worth every cent.

Common Pitfalls to Avoid

Oversized Turbo: A 90mm turbo on a 5.7 may look cool but will lag until 4500+ rpm, making the car frustrating to drive on the street.
Inadequate Fuel System: Starving the engine of fuel at high rpm causes lean detonation. Always test fuel pressure at the rail under load.
Skipping Intercooler: Hot intake air drastically reduces power and invites knock. Even a moderate intercooler pays huge dividends.
Ignoring Heat Management: Turbo blankets, ceramic coatings, and heat wrapping of pipes near the intake help keep IATs in check.
Not Upgrading Clutch or Torque Converter: Slip under boost generates heat and ruins components. Upgrade first.

Budget Overview for 700+ HP 5.7 Hemi Build

Costs vary widely, but a realistic parts-only budget for a reliable 700+ hp single turbo build is:

Turbo kit (manifold, turbo, wastegate, BOV, piping, intercooler): $3,500–$6,000
Fuel system (pump, injectors, regulator, lines): $1,200–$2,000
Standalone ECU or tuning package: $1,500–$3,000
Forged pistons and rods: $1,500–$2,500
Camshaft and valvetrain: $600–$1,200
Head studs and gasket: $300–$500
Cooling upgrades (radiator, fans, oil cooler): $500–$1,000
Transmission upgrades: $1,000–$3,000

Total estimated parts cost: $10,000–$19,000 plus labor if not DIY. With proper planning, a reliable 700+ wheel horsepower 5.7 Hemi turbo build is achievable without breaking the bank, as long as every supporting mod is addressed.

Conclusion

Taking a 5.7 Hemi from 500 to 700+ horsepower with turbocharging is a rewarding project that transforms the vehicle’s character. The key to success lies in matching turbo size to the intended power target, investing in a comprehensive fuel system, upgrading the engine’s internal components for longevity, and properly tuning the combination. Avoid shortcuts; reliability rides on the quality of every supporting modification. With the right approach, your 5.7 Hemi can deliver neck-snapping power that rivals larger-displacement engines, all while maintaining street manners.

For further reading, consult resources like HP Tuners for detailed tuning forums, LX Forums for chassis-specific builds, and Precision Turbo for compressor maps and tech articles.