550+RWHP Daily-Driver 4.2L turbo inline-six 

Expected Q4 2026 release — early build slots and pre-orders available now

Not everyone needs another V8.

The straight-six has always had its own appeal: smooth, durable, unmistakable sound, and a layout that is naturally balanced in both first- and second-order forces. That inherent smoothness is why engineers kept using inline-sixes in everything from basic American cars and trucks to some of the best luxury and performance cars ever built.

The Atlas 4200 takes that familiar straight-six personality and adds the hardware expected from a modern performance engine: an aluminum block, dual overhead cams, four valves per cylinder, variable cam timing, electronic throttle control, standalone engine management, flex fuel, and turbocharging.

For anyone familiar with the 2JZ, the comparison is hard to ignore.

The Atlas offers:

• Approximately 40% more displacement
• A roughly 375-pound aluminum long block
• Hundreds of pounds less mass than many complete iron-block 2JZ swap combinations
• Variable cam timing as standard equipment
• A significantly broader street powerband at the 500–600 RWHP level

The 2JZ has a massive aftermarket and proven four-digit horsepower capability. That is not the point of the Atlas. For a street car in the 500–600 RWHP range, the Atlas starts with more displacement, far less weight, and the ability to use cam timing to improve response and torque throughout the operating range.

That means earlier boost, stronger torque before peak horsepower, less weight over the front of the car, and more power under the curve without needing excessive boost or extreme engine speed.

RAD builds the Atlas around the way a serious street car should actually behave. It should fire immediately hot or cold, idle cleanly, stay smooth in traffic, respond crisply to the throttle, and deliver consistent performance as temperature, weather, fuel blend, and elevation change.

The package is designed around 500–600 RWHP, pump-gas operation with standard flex-fuel capability, and a broad turbocharged powerband that makes the car feel strong everywhere.

This is far more than a crate long block. The complete engine, turbo system, intake, fuel and ignition hardware, standalone ECU, engine harness, tune, testing, documentation, and available transmission integration are developed and supplied as one complete RAD powertrain package.

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Atlas 4200 Specifications

Performance and Drivability

• 500–600 RWHP package range
• Broad, responsive torque curve with strong power through the middle of the tach
• Fast turbo response without an oversized, lazy turbocharger
• Smooth and linear throttle response
• Stable idle with normal accessory and electrical loads
• Clean cold starts, hot starts, and heat-soaked restarts
• Consistent fueling and boost control across changing weather and elevation
• Pump-gas operation with standard flex-fuel capability
• Fully tuned before delivery
• Limited remote fine-tuning available after installation for throttle response, final vehicle setup, and driver preference

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4.2L LL8-Based Engine

• 4.2L Atlas LL8-based inline-six
• Aluminum block and aluminum 24-valve cylinder head
• Dual overhead camshafts with variable intake cam timing
• Seven-main-bearing crankshaft support
• Electronic drive-by-wire throttle
• Port fuel injection
• Coil-on-plug ignition
• Factory crankshaft and camshaft position sensing
• Naturally balanced inline-six layout with exceptionally low vibration and harshness

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Fully Blueprinted Long Block

Every RAD engine is completely disassembled, inspected, measured, corrected, assembled, and documented.

• Cylinder bores measured for diameter, taper, out-of-round, and piston clearance
• Main bores, deck flatness, and deck height checked
• Crankshaft journals measured for size, taper, runout, and surface condition
• Connecting rods inspected for alignment, big-end dimensions, side clearance, and fastener preload
• Pistons inspected, measured, and prepared for the final combination
• Ceramic piston coatings used where specified
• Rotating assembly balanced and checked for final rotating torque
• RAD-specified piston rings gapped for turbocharged operation
• RAD-specified main and rod bearings with clearances set for the intended oil, temperature, and load
• Compression ratio, piston deck position, quench, crankshaft endplay, and rod side clearance measured
• Oil passages, galleries, threaded holes, plugs, and sealing surfaces inspected
• New RAD-specified gaskets, seals, fasteners, and assembly hardware throughout
• Complete build measurements recorded for the finished engine

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Cylinder Head and Valvetrain

The Atlas does not require a large camshaft or rough idle to make the intended power. Displacement, four-valve airflow, VVT, and boost provide the performance without sacrificing street manners.

• Cylinder head fully disassembled, cleaned, inspected, and prepared
• Performance valve job with valve sealing and seat concentricity verified
• Valve guides, stems, chamber volume, head flatness, and installed height measured
• RAD-specified valve springs with seat pressure, open pressure, and coil-bind clearance checked
• Matched retainers and locks
• Cam timing and VVT operation verified
• Optional RAD-spec camshaft package available where additional airflow is justified
• Piston-to-valve and valvetrain clearances checked throughout the full cam-phasing range
• VVT tuned to improve turbo response, midrange torque, and upper-RPM airflow

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Complete Turbo System

Turbocharging does not need to be complicated.

The Atlas package includes the complete engine-side turbo system, already matched, assembled, and plumbed. There is no need to piece together a turbo, wastegate, blow-off valve, oil lines, fittings, boost controller, and manifold from unrelated parts.

• Premium turbocharger from an established OEM manufacturer
• Turbo selected around the intended powerband, displacement, and street response
• Integrated internal wastegate
• Integrated compressor bypass valve
• Fabricated turbo exhaust manifold
• Complete turbo oil-feed and drain system
• Required fittings, lines, heat protection, and mounting hardware
• Electronic boost-control solenoid
• Closed-loop boost management through the standalone ECU
• Boost targets adjusted for fuel blend, operating conditions, and engine protection
• Intake temperature, manifold pressure, and turbo-system monitoring
• Complete engine-side turbo system assembled and plumbed before delivery

The result is the easy button for a turbocharged build: properly selected components, clean packaging, predictable boost control, and a turbo that works with the engine instead of fighting it.

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Intake and Charge-Air Hardware

• Forward-facing performance intake manifold
• Runner and plenum design selected for strong midrange and upper-RPM airflow
• Electronic drive-by-wire throttle body
• E85-compatible fuel rails, injectors, and mounting hardware
• MAP and post-intercooler intake-air-temperature sensors
• Vacuum and boost-reference provisions
• Engine-side charge-pipe connection
• Supplied sizing recommendations for intercooler, charge piping, air filter, and turbo inlet

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Fuel, Ignition, ECU, and Tune

Flex fuel is standard on every RAD powertrain.

• High-flow E85-compatible injectors sized for the final power level
• Flex-fuel composition sensor
• Fuel-pressure sensor
• Wideband oxygen sensor
• Coil-on-plug ignition with RAD-specified spark plugs
• Standalone ECU and complete labeled engine harness
• Full control of drive-by-wire throttle, VVT, boost, fuel pumps, cooling fans, and flex-fuel blending
• Oil pressure, oil temperature, fuel pressure, coolant temperature, manifold pressure, and intake temperature monitoring
• Engine-protection strategies for oil pressure, fuel pressure, boost, mixture, and temperature
• 93-octane and E85 tuning with automatic blending between fuel types
• 91- and 89-octane configurations available
• Complete hot-start, cold-start, idle, part-throttle, boost, and wide-open-throttle tune
• High-speed data logging
• Tachometer, speedometer, and factory-gauge interface provisions
• Full ECU/TCU integration where equipped with the ZF 8HP
• No additional local tuner required before the vehicle can be driven

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Transmission Configurations

Engine Package

For customers retaining an existing manual transmission or mechanically controlled automatic.

• Complete turbocharged Atlas engine package
• Standalone ECU and engine harness
• Full engine tune
• Engine-side fuel, ignition, cooling, oiling, and turbo hardware
• Flywheel, flexplate, and transmission-adapter options available based on application

AR5 Five-Speed Manual

A compact and cost-effective manual option well suited to street-driven Atlas combinations.

• AR5 five-speed transmission
• Matched bellhousing arrangement
• RAD-specified clutch and flywheel
• Hydraulic release system
• Shifter and vehicle-speed provisions
• Complete engine tune matched to the transmission

T56 Magnum Six-Speed Manual

For customers who want greater torque capacity and six forward ratios.

• Application-appropriate T56 Magnum configuration
• RAD-specified clutch, flywheel, and hydraulic release system
• Shifter configuration selected around the final installation
• Vehicle-speed provisions
• Complete engine tune matched to the transmission and gearing

ZF 8HP Automatic

The premium Atlas powertrain package.

• Rear-wheel-drive ZF 8HP transmission
• Factory internal transmission controller
• Full standalone ECU and TCU integration
• Coordinated engine torque management during shifts
• Tuned shift timing, firmness, and converter lockup
• Automatic, sport, and manual-shift behavior
• Optional paddle-shift capability
• Transmission temperature, gear-position, and vehicle-speed outputs
• Engine and transmission tuned and tested together as one system

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Oiling, Cooling, and Engine-Side Hardware

• Application-appropriate oil pan and pickup
• RAD-specified oil-control components
• Oil pressure and oil temperature sensors
• Engine-side oil, coolant, fuel, and vacuum fittings
• Accessory-drive components as specified
• Thermostat and coolant-outlet provisions
• Engine-side heater and radiator connections
• Ports and provisions for aftermarket or original gauge senders
• Supplied cooling-system, fuel-system, exhaust, and fluid specifications

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Dyno Testing and Validation

• Controlled initial startup and heat cycling
• Oil pressure, fuel pressure, coolant flow, sensor, and wiring verification
• Engine break-in under controlled load
• Part-throttle and steady-state dyno testing
• Turbo response and closed-loop boost testing
• Hot-start, heat-soak, and full-operating-temperature testing
• High-load and full-power dyno testing
• Flex-fuel operation verified
• Compression, leakdown, fluid, filter, and datalog review before delivery
• Final power and torque documentation
• Final engine and transmission tune files supplied

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Included Documentation and Support

• Complete engine build documentation
• Recorded blueprint measurements
• Major component specifications
• ECU and tune files
• Engine and chassis wiring diagrams
• Clearly identified power, ground, ignition, starter, gauge, and vehicle-speed connections
• Startup and commissioning instructions
• Fluid and service specifications
• Fuel-system sizing requirements
• Cooling-system sizing requirements
• Intercooler and charge-pipe recommendations
• Exhaust sizing recommendations
• Tachometer, speedometer, and gauge-interface guidance
• Limited remote startup and fine-tuning support

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Reserve an Early Atlas Build

The Atlas 4200 combines the best parts of the straight-six formula: natural smoothness, durability, distinctive sound, modern cylinder-head airflow, variable cam timing, low weight, and a turbocharged powerband built for the street.

It offers roughly 40% more displacement than a 3.0L turbo-six, starts with a dramatically lighter aluminum engine, and delivers the kind of area under the curve that matters every time the car leaves a stoplight, rolls into the throttle, or pulls through the next gear.

It is different without being difficult—and fast without giving up the manners that make the car worth driving.

Expected release: Q4 2026

RAD is accepting pre-orders and deposits for early Atlas 4200 engine and complete powertrain builds now. Initial build slots are expected to carry a 12–16 week lead time.

Contact RAD to reserve a build position and configure the engine, transmission, fuel, and power level around your project.

RAD — Engineered Powertrain Solutions. Ready to Drive.