Garrett G-Series II G40-1250 71mm Turbocharger

Garrett G-Series II G40-1250 71mm Turbocharger — Select Turbine Housing

Part Number: 938272-5002S

The Garrett G-Series II G40-1250 is a standard-rotation, dual-ceramic-ball-bearing turbocharger platform designed for high-output street, competition, and specialty-performance applications requiring substantial compressor flow in Garrett’s G40 frame. Garrett rates the G40-1250 for 500–1,250 horsepower and references engine displacements from 2.0 to 6.0 liters. Garrett horsepower ratings represent potential flywheel horsepower based on compressor-map airflow and are not a guaranteed wheel-horsepower figure.

The G40-1250 uses a 71mm inducer and 88mm exducer compressor wheel with a 65-trim profile and 0.80 compressor-housing A/R. The turbine stage uses a 77mm inducer and 70mm exducer wheel with an 84-trim profile. Compared with the G40-1000, the G40-1250 retains the same turbine dimensions and housing family while using the larger 71mm compressor, making it appropriate where the application requires greater compressor-flow capability without moving to the larger G42 frame.

As part of Garrett’s G-Series II range, the G40-1250 incorporates revised compressor aerodynamics that provide up to 10 percent greater compressor flow than the corresponding first-generation G-Series unit at peak pressure ratio and peak turbocharger speed. Garrett also identifies increased efficiency at high flow rates. G-Series II retains the corresponding first-generation standard-rotation G40 compressor- and turbine-housing interfaces, permitting an existing G40 installation to be upgraded when all reused housing part numbers and interfaces are confirmed.

This listing is structured as a selectable-housing product. The Garrett 938272-5002S supercore may be combined with one of eight verified standard-rotation G40 turbine housings. Four open-scroll housings use V-band turbine inlets, while four divided housings use T4 turbine inlets. Every available housing uses a V-band turbine outlet and requires an external wastegate. Garrett does not list an internally wastegated G40-1250 assembly.

RAD recommends the 1.06 A/R open-scroll V-band inlet and V-band outlet housing, Garrett part number 757707-0029, as the general catalog default. It provides more turbine-flow capacity than the 0.85 and 0.95 A/R housings while avoiding the slower response and more specialized operating range associated with the largest 1.19 A/R option. The open-scroll V-band configuration also avoids the manifold and pulse-separation requirements of a divided T4 system. Final housing selection should still be based on engine displacement, airflow, power target, exhaust-manifold design, turbine inlet pressure, and intended operating range.

Key Features

• Garrett G-Series II G40-1250 standard-rotation turbocharger platform
• Garrett horsepower reference range: 500–1,250 hp
• Garrett displacement reference range: 2.0–6.0 liters
• 71mm compressor inducer and 88mm compressor exducer
• 77mm turbine inducer and 70mm turbine exducer
• Dual ceramic ball-bearing center section
• G-Series II compressor aerodynamics with up to 10 percent more flow than the corresponding first-generation G-Series compressor at peak pressure ratio and peak turbo speed
• Increased compressor efficiency at high flow rates
• One-piece center-housing and backplate architecture
• Twin piston-ring sealing on both sides of the shaft assembly
• High-temperature turbine-wheel construction
• Stainless-steel turbine housings rated by Garrett for temperatures up to 1,050°C
• Machined compressor-housing port for an optional Garrett turbo-speed sensor
• Four open-scroll V-band inlet configurations
• Four divided T4 inlet configurations
• V-band turbine outlet on every verified housing
• External-wastegate configuration on every verified housing
• Compatible with the verified standard-rotation Garrett G40 housing family listed below

Kit Includes

• Garrett G-Series II G40-1250 supercore, part number 938272-5002S
• Compressor housing
• Forged and fully machined compressor wheel
• Center housing rotating assembly
• Turbine wheel
• Selected Garrett G40 turbine-housing kit when a complete housing variant is ordered
• Garrett gasket kit packaged with the selected turbine-housing kit
• Supercore-only variant excludes the turbine housing

Technical Specifications

Compressor

• Compressor inducer: 71mm
• Compressor exducer: 88mm
• Compressor trim: 65
• Compressor-housing A/R: 0.80
• Compressor inlet: approximately 4.00-inch hose connection
• Compressor outlet: approximately 2.50-inch hose connection
• Optional Garrett turbo-speed sensor hardware is sold separately

Turbine

• Turbine inducer: 77mm
• Turbine exducer: 70mm
• Turbine trim: 84
• Turbine-housing material: stainless steel
• Turbine-housing temperature rating: up to 1,050°C
• Available turbine-housing A/R values: 0.85, 0.95, 1.06, and 1.19
• Available turbine inlets: open-scroll V-band or divided T4
• Turbine outlet: V-band on every listed housing
• Wastegate arrangement: external wastegate required for every listed housing

Center Housing, Bearings, Lubrication, and Coolant Connections

• Bearing system: dual ceramic ball bearing
• Cooling: water cooled
• Engine-oil supply and gravity oil drain required
• Oil-feed components, any required restrictor, and engine-side adapter must be selected for the application
• Oil-drain flange, gasket, hose, fittings, and engine-side drain provision are not included
• Coolant fittings, hoses, and engine-side connections must be confirmed for the selected installation
• Oil pressure, feed restriction, drain sizing, and drain routing must follow Garrett’s installation requirements for the specific engine and oiling system

Available Turbine Configurations

• 0.85 A/R V-Band / V-Band — Garrett 757707-0027: open-scroll V-band turbine inlet, V-band turbine outlet, external wastegate required.
• 0.95 A/R V-Band / V-Band — Garrett 757707-0028: open-scroll V-band turbine inlet, V-band turbine outlet, external wastegate required.
• 1.06 A/R V-Band / V-Band — Garrett 757707-0029: open-scroll V-band turbine inlet, V-band turbine outlet, external wastegate required. RAD recommended general catalog default.
• 1.19 A/R V-Band / V-Band — Garrett 757707-0030: open-scroll V-band turbine inlet, V-band turbine outlet, external wastegate required.
• 0.85 A/R Divided T4 / V-Band — Garrett 757707-0032: divided T4 turbine inlet, V-band turbine outlet, external wastegate required.
• 0.95 A/R Divided T4 / V-Band — Garrett 757707-0033: divided T4 turbine inlet, V-band turbine outlet, external wastegate required.
• 1.06 A/R Divided T4 / V-Band — Garrett 757707-0034: divided T4 turbine inlet, V-band turbine outlet, external wastegate required.
• 1.19 A/R Divided T4 / V-Band — Garrett 757707-0035: divided T4 turbine inlet, V-band turbine outlet, external wastegate required.
• Supercore Only — Garrett 938272-5002S: compressor housing and complete center rotating assembly supplied without a turbine housing.

Application Notes

• This is a universal performance turbocharger and is not a vehicle-specific bolt-on assembly.
• Garrett’s 500–1,250 horsepower range is a compressor-based flywheel-horsepower reference. Actual output depends on engine airflow, fuel, charge-air temperature, exhaust-manifold design, turbine housing, boost pressure, backpressure, and tune.
• The G40-1250 uses the same 77/70mm turbine dimensions and standard-rotation G40 housing family as the G40-1000, but its larger 71mm compressor is intended for greater airflow and power capability.
• The 0.85 and 0.95 A/R housings prioritize earlier boost response and may increase turbine inlet pressure as airflow and power rise.
• The 1.06 A/R housings provide the broadest general balance between response and turbine-flow capacity for many high-output street and track applications.
• The 1.19 A/R housings provide the greatest exhaust-flow capacity in the verified G40 family and are best suited to applications that can accept slower boost response.
• The open-scroll V-band housings are generally the simpler choice for custom single-turbo systems because they do not require a true divided manifold and pulse-preserving wastegate arrangement.
• The divided T4 housings should be used with a properly divided manifold and an external-wastegate arrangement that preserves the intended pulse separation. Installing a divided housing on an undivided manifold does not provide the same twin-scroll behavior.
• No internally wastegated G40-1250 configuration is listed by Garrett. An appropriately sized external wastegate system is required.
• The G40-1250 supercore is compatible only with the verified standard-rotation G40 housings listed in this description. Reverse-rotation housings are not interchangeable.
• G-Series II uses the corresponding first-generation G40 compressor- and turbine-housing interfaces, but every existing installation should be confirmed by part number before components are reused.
• Turbine-inlet flange or clamp, turbine-outlet weld flange and clamp, external wastegate, wastegate springs, oil-feed hardware, oil-drain hardware, coolant plumbing, intake plumbing, charge piping, exhaust manifold, downpipe, boost-control hardware, and application-specific fasteners are not included unless separately stated.
• Garrett turbo-speed monitoring hardware and electronic boost-control components are sold separately.
• Final turbocharger and turbine-housing selection should be based on an engine-airflow model and intended operating range rather than displacement or peak-power target alone.

Emissions and Competition-Use Notice

This universal performance turbocharger is intended for racing and competition applications. Vehicle modifications must comply with all applicable emissions, registration, noise, and road-use requirements. It is the purchaser’s responsibility to determine whether the product is legal for the intended vehicle and use.