Garrett G40: Specs, Fitment, and Is It Worth It

The Garrett G40 turbocharger is the large-frame entry in Garrett's G-Series platform, designed for builds targeting 900 to 1250 horsepower on both diesel and gasoline engines with the displacement and airflow volume to support that power range. Where the G25 and G30 serve mid-range performance builds, the G40 fills the role of a high-capacity single turbocharger for engines that exceed what smaller frames can support -- large-cubic-inch diesel trucks, big-block gasoline platforms, and compound turbo arrangements where the G40 functions as the low-pressure unit supplying a smaller high-pressure turbo. The Garrett G40 is available in G-Series II CHRA configurations (G40-1000 and G40-1250) and original-generation Super Cores (G40-900 and G40-1150), all paired with separately ordered turbine housing kits that allow A/R selection and inlet/outlet configuration to match the application. This guide covers G40 specifications, the modular build system, how to select the correct configuration, and whether this Garrett turbocharger is the right choice for the build.

Garrett G40 Specifications and Platform Overview

The G40 uses a 76mm compressor wheel inducer, which places it in the large-frame single turbo category. The compressor map covers mass flow rates appropriate for 900-1250 hp output depending on the specific rotating assembly and engine displacement. Garrett offers the G40 in two generations:

• G40 G-Series II (current generation): G40-1000 rated to 1000 hp; G40-1250 rated to 1250 hp; updated G-Series II CHRA with improved compressor map, revised bearing preload, and wider efficiency island compared to the first-generation Super Core; available as CHRA-only (cartridge) or Super Core (CHRA plus compressor housing) -- turbine housing ordered separately
• G40 Original Super Core (first generation): G40-900 rated to 900 hp; G40-1150 rated to 1150 hp; available as standard-rotation Super Core assemblies; turbine housing ordered separately; superseded in the G-Series II lineup but still available for applications already configured around the original compressor map

The G40 is a modular platform -- the Super Core or CHRA provides the rotating assembly and compressor section, and the turbine housing kit is selected separately. Turbine housing options include divided T4 inlet with V-Band outlet (T4/V-Band) and open V-Band inlet with V-Band outlet (O/V V-Band), in four A/R options: 0.85, 0.95, 1.06, and 1.19. The T4 inlet configuration mates to T4-flanged exhaust manifolds common on diesel platforms; the O/V V-Band allows mounting in any rotation on a V-Band exhaust manifold. Neither G40 configuration is engine-specific -- the G40 requires a custom or universal exhaust manifold, oil feed and return lines, and coolant connections for the water-cooled center housing.

Top Picks: Garrett G40 Turbocharger Configurations

For a new build targeting the upper end of the G40 power range, the Garrett G40-1250 G-Series II Super Core Assembly (938272-5002S) is the recommended starting point. The G-Series II CHRA delivers a wider compressor map and improved efficiency island position over the original G40-1150 it replaces, and the 1250 hp rating provides headroom above the 1000 hp target that most large single-turbo diesel and gasoline builds actually need. The Super Core includes the CHRA and compressor housing as an assembled unit, ready to mate with the separately selected turbine housing kit. For a build targeting 1000 hp with the current G-Series II CHRA, the Garrett G40-1000 G-Series II Super Core Assembly (938272-5001S) delivers the same G-Series II bearing and compressor technology in the 1000 hp-rated configuration.

For the turbine housing, the Garrett G40 Turbine Housing Kit O/V V-Band / V-Band 0.95 A/R (757707-0028) is the most versatile starting point for a large diesel single-turbo application. The 0.95 A/R V-Band/V-Band configuration allows mounting in any orientation on a V-Band exhaust manifold and provides a balanced spool-to-flow tradeoff that works across a wide range of large-displacement diesel builds. Builds with smaller displacement or those prioritizing low-RPM response should consider the 0.85 A/R; builds with larger displacement or those optimizing for peak power over spool speed should consider the 1.06 or 1.19 A/R. Browse the complete Garrett G-Series large-frame turbocharger catalog for all G40 Super Core, CHRA, and turbine housing configurations.

Match to the Build

• Large-displacement diesel single-turbo build at 900-1000 hp: The G40-1000 G-Series II Super Core with a 0.95 or 1.06 A/R turbine housing is the correct configuration for a large single on a 6.7L Cummins, 6.6L Duramax, or 6.7L Power Stroke build targeting 900-1000 hp -- the 76mm compressor flows the mass required at those power levels on these engine displacements, and the G-Series II map maintains efficiency at the flow rates the engine demands
• Maximum-effort diesel single-turbo build at 1100-1250 hp: The G40-1250 G-Series II Super Core with a 1.06 or 1.19 A/R turbine housing is the configuration for builds pushing toward the G40's rated limit; the larger A/R turbine housing allows more exhaust energy flow at the elevated engine output these power levels require, reducing exhaust backpressure that costs power and raises EGTs at peak load
• Low-pressure unit in a compound turbo diesel arrangement: The G40's large compressor frame makes it suitable as the atmospheric-side (low-pressure) turbocharger in a compound arrangement on a large diesel platform; the G40 draws in atmospheric air, compresses it to an intermediate pressure, and feeds that pre-compressed charge to the factory or high-pressure second-stage turbo; A/R selection for the low-pressure position is typically larger than a standalone configuration to reduce restriction at the high flow rates the compound system processes
• Large-displacement gasoline performance engine at 1000+ hp: The G40 supports large gasoline platform builds where the engine displacement and airflow volume justify the 76mm frame; correct A/R selection is critical -- gasoline engines typically require a tighter A/R than diesel platforms of similar displacement to build boost within the gasoline engine's narrower RPM-to-flow operating window

Signs the Existing Turbocharger Needs Upgrade or Replacement

• Power output plateauing below the tune's target at wide-open throttle -- the current turbocharger reaching its maximum mass flow rate before the engine reaches its power peak; characteristic of a compressor that is correctly sized for a lower power target but undersized for the current build level; moving to a G40 corrects this when the displacement and fueling capacity of the engine justify the larger compressor frame
• Compressor surge at elevated boost -- a rhythmic flutter or stutter under boost indicating the compressor operating beyond its stable flow range; the G40's wider compressor map moves the surge line outward and eliminates this condition in builds where the existing turbo's surge margin is insufficient
• Excessive exhaust backpressure above peak power -- a turbine housing that is undersized for the engine's exhaust volume creating restriction that limits top-end power; the G40's turbine housing range, particularly the 1.06 and 1.19 A/R options, provides substantially more exhaust flow capacity than smaller-frame turbine sections
• Oil consumption, shaft play, or compressor seal wear on the existing large-frame unit -- physical wear requiring replacement; the G40 G-Series II provides a fresh rotating assembly with current bearing specifications and seal tolerances when the existing large-frame turbo reaches end of service life

Frequently Asked Questions

Does the Garrett G40 come as a complete assembled turbocharger?

The G40 is sold as a modular system -- the Super Core (CHRA plus compressor housing) and the turbine housing kit are separate purchases that assemble into a complete turbocharger. The G40-1000 and G40-1250 G-Series II Super Cores, the G40-900 and G40-1150 original Super Cores, and CHRA-only cartridges are each listed as individual products. The turbine housing is selected separately based on the required inlet configuration (T4 or V-Band) and A/R ratio for the application. Both components are required to build a complete turbocharger assembly.

What is the difference between the G40 G-Series II and the original G40 Super Core?

The G40 G-Series II uses Garrett's updated G-Series II CHRA with a revised compressor wheel profile and improved bearing preload design that widens the efficiency island and raises the peak flow rating compared to the original generation. The G40-1000 G-Series II replaces the G40-900 original, and the G40-1250 G-Series II replaces the G40-1150 original. For a new build, the G-Series II is the current Garrett recommendation. The original Super Cores remain available for applications where the first-generation compressor map characteristics are specifically required.

Bottom Line

The Garrett G40 turbocharger covers the 900-1250 horsepower range in a 76mm large-frame modular platform built for maximum-effort diesel and gasoline builds. The G-Series II CHRA in the G40-1000 and G40-1250 configurations delivers a wider compressor map and improved efficiency over the original generation. Select the Super Core based on the power target, pair it with a turbine housing at the A/R that matches the engine's displacement and RPM band, and configure the inlet and outlet for the exhaust manifold on the application. The G40 is purpose-built for builds that have outgrown smaller-frame options and need a single turbocharger capable of sustaining four-digit horsepower output.