Holset HX35 vs HX40 vs HE351: Specs, Sizes & Applications

The Holset HX35, HX40, and HE351 are three distinct turbocharger platforms designed by Holset (now Cummins Turbo Technologies) for different diesel engine sizes, power ranges, and duty cycles.

This guide covers individual turbo specifications and factory applications, physical size and housing comparisons, airflow capacity and spool-up behavior, best-use applications and swap compatibility, and common part numbers for each platform.

The HX35 is a fixed-geometry, wastegate-equipped turbo built for the Cummins 5.9L 12-valve and 24-valve ISB engines. Its 54–58 mm compressor wheel supports 300 to 450 horsepower and delivers fast spool-up, making it one of the most recognized Holset turbos in both pickup truck and light industrial applications.

The HX40 steps up to a 60–62 mm compressor wheel and larger turbine housing, supporting 400 to 600 horsepower across Cummins 6BT, 8.3L, and ISC/ISL platforms. Its higher airflow ceiling suits performance builds, heavy equipment, and larger displacement engines that operate at sustained high loads.

The HE351 introduces variable geometry turbine (VGT) technology on models like the HE351VE, using electronic vane control to eliminate the traditional wastegate. Factory-equipped on 2004.5-and-later Dodge Ram trucks with the Cummins 5.9L and 6.7L ISB, the HE351 delivers the fastest spool of the three while supporting 325 to 500 horsepower.

We also cover physical swap requirements between all three platforms, including downpipe modifications, oil and coolant line differences, and emissions compliance considerations. Specific part numbers for each turbo family help identify the correct configuration for your engine and application.

What Is the Holset HX35 Turbocharger?

The Holset HX35 turbocharger is a fixed-geometry, wastegate-equipped turbo designed by Holset (now Cummins Turbo Technologies) for medium-duty diesel engines. Below, the key specs, wheel sizes, and factory applications break down what defines this popular unit.

What Are the Key Specs of the HX35?

The key specs of the HX35 include a journal-bearing center section, an internal wastegate for boost control, and a T3 turbine inlet flange. The HX35 supports approximately 300 to 500 horsepower depending on compressor trim and housing configuration. Boost pressure typically ranges from 15 to 30 psi in factory calibrations.

Key specifications include:

• Bearing type: journal bearing (oil-lubricated)

• Wastegate: internal

• Turbine inlet flange: T3

• Approximate horsepower range: 300–500 hp

• Typical boost pressure: 15–30 psi

For most mid-range Cummins applications, the HX35 strikes a practical balance between spool speed and airflow capacity, making it one of the more versatile units in the Holset lineup.

What Compressor and Turbine Wheel Sizes Does the HX35 Use?

The HX35 uses a compressor wheel diameter of approximately 54–58 mm and a turbine wheel diameter of approximately 54–56 mm, though exact dimensions vary by part number and trim level. The compressor housing typically features a 4-inch inlet and 2.5-inch outlet. Turbine housing A/R ratios commonly range from 0.60 to 0.80, with the lower values promoting quicker spool and the higher values favoring top-end flow.

These relatively compact wheel sizes keep exhaust energy threshold low, which is why the HX35 responds well at lower engine speeds compared to larger Holset models.

What Engines and Vehicles Come Factory with the HX35?

The engines and vehicles that come factory with the HX35 include the Cummins 5.9L 12-valve and 24-valve ISB engines, most notably in the 1994–2002 Dodge Ram 2500 and 3500 pickups. Cummins also specified the HX35 on select industrial and agricultural 4BT and 6BT engine platforms.

Common factory applications include:

• 1994–1998 Dodge Ram with the 5.9L 12-valve Cummins (P7100 fuel system)

• 1998–2002 Dodge Ram with the 5.9L 24-valve Cummins (VP44 fuel system)

• Cummins 6BT industrial and generator-set configurations

• Cummins 4BT in select light industrial equipment

The HX35's widespread use across these platforms established it as one of the most recognized Holset turbochargers in the diesel aftermarket, creating strong parts availability and rebuild support. Understanding how the HX35 compares in size helps clarify when a larger turbo like the HX40 may be a better fit.

What Is the Holset HX40 Turbocharger?

The Holset HX40 turbocharger is a fixed-geometry, medium-frame turbo designed by Holset (now Cummins Turbo Technologies) for mid-range to heavy-duty diesel engines. Its larger compressor and turbine wheels support higher airflow than the HX35, making it suited for engines producing 350–600+ horsepower. Below, the key specs, wheel sizes, and factory applications break down what defines this turbo.

What Are the Key Specs of the HX40?

The key specs of the HX40 include a journal-bearing center section, a T3 or T4 turbine inlet flange (depending on the application), and a compressor housing that typically uses a 4-inch inlet and 2.5-inch outlet. Turbine housing A/R ratios commonly range from 0.76 to 1.15, allowing tuners to match exhaust energy to specific engine displacement and power targets. The HX40 supports boost pressures from roughly 20 to 45+ psi in properly configured setups. For builders stepping up from smaller Holset frames, the HX40's larger housing volume and higher flow ceiling make it a natural mid-range upgrade worth serious consideration.

What Compressor and Turbine Wheel Sizes Does the HX40 Use?

The HX40 uses compressor wheels ranging from approximately 56 mm to 62 mm inducer diameter, paired with turbine wheels typically measuring 60 mm to 67 mm. These larger wheels move significantly more air than HX35-class components, which is why the HX40 produces higher peak airflow at the cost of slightly slower spool-up. Common compressor trim values fall between 56 and 62, while turbine trims generally range from 78 to 96. The specific wheel combination determines where in the RPM band the turbo reaches peak efficiency. Matching the correct compressor-to-turbine wheel ratio is critical for balancing response with top-end power.

What Engines and Applications Come Factory with the HX40?

The engines and applications that come factory with the HX40 span several Cummins platforms and industrial sectors. Key factory pairings include:

• Cummins 6BT and 6BTA 5.9L engines in medium-duty truck and equipment applications.

• Cummins 8.3L (6C/6CT) engines used in construction, agricultural, and marine equipment.

• Select Cummins ISC and ISL engines in bus, vocational, and industrial configurations.

• Heavy equipment from manufacturers such as Komatsu, Case, and Hyundai using Cummins power.

The HX40's broad factory fitment across both on-highway and off-highway platforms reflects its versatility as a mid-frame turbo capable of supporting diverse duty cycles. Understanding which engine originally paired with the HX40 helps narrow down the correct part number and housing configuration.

What Is the Holset HE351 Turbocharger?

The Holset HE351 turbocharger is a variable geometry turbo (VGT) designed by Holset (Cummins Turbo Technologies) for medium-duty diesel engines. Below, we cover its key specs, wheel sizes, and factory applications.

What Are the Key Specs of the HE351?

The key specs of the HE351 include a variable geometry turbine (VGT) design that adjusts exhaust flow electronically, eliminating the need for a wastegate. This turbo uses a single-piece, cast compressor wheel paired with a variable nozzle turbine assembly controlled by an electric actuator. The bearing system is a full-floating journal bearing design with an integrated oil and coolant supply. Rated boost pressure typically ranges from 25 to 35 psi in factory configurations. For anyone maintaining modern emissions-equipped Cummins trucks, the HE351's electronic controls make it more complex to service than fixed-geometry alternatives like the HX35 or HX40.

What Compressor and Turbine Wheel Sizes Does the HE351 Use?

The HE351 uses compressor wheels measuring approximately 58 mm (inducer) to 82 mm (exducer) in common VE variant configurations. Turbine wheel diameters typically range from 62 mm to 68 mm, depending on the specific model designation. Two primary variants exist:

• The HE351VE features a 58/82 mm compressor wheel and a variable geometry turbine with electronically actuated sliding nozzle vanes.

• The HE351CW uses a similar compressor frame with revised turbine housing geometry for later-model Cummins ISB applications.

These wheel dimensions place the HE351 between the HX35 and HX40 in compressor sizing, though its variable geometry design fundamentally changes how it delivers boost across the RPM range.

What Engines and Vehicles Come Factory with the HE351?

The engines and vehicles that come factory with the HE351 include several Cummins ISB 6.7-liter platforms. Primary OEM applications are:

• Dodge/Ram 2500 and 3500 (2007.5–2018): Equipped with the Cummins 6.7L ISB, these trucks use HE351VE and HE351CW variants paired with diesel particulate filter (DPF) and selective catalytic reduction (SCR) aftertreatment systems.

• Cummins ISB 6.7 industrial and medium-duty truck applications: Found in Freightliner, Kenworth, and Peterbilt medium-duty chassis using the same 6.7L engine platform.

The HE351's variable geometry design was specifically chosen to meet increasingly strict emissions regulations while maintaining strong low-RPM response for towing applications. Understanding where each turbo fits in the Holset lineup helps clarify how the HX35, HX40, and HE351 compare in overall size and mounting.

How Do the HX35, HX40, and HE351 Compare in Size?

The HX35, HX40, and HE351 compare in size across compressor housing volume, turbine housing A/R ratio, and overall mounting dimensions. Each difference affects airflow capacity and fitment.

How Do the Compressor Housings Compare Across All Three?

The compressor housings compare across all three turbos primarily in inlet diameter, outlet size, and volute volume. The HX35 uses the smallest compressor housing, typically accepting a compressor wheel in the 54–58 mm inducer range. The HX40 steps up with a larger volute designed for wheels in the 58–62 mm range, moving significantly more air at higher boost levels. The HE351, though closer to the HX35 in external footprint, features a modernized housing design optimized for faster airflow velocity. When choosing between them, compressor housing size should match your target airflow; oversizing creates lag, while undersizing caps horsepower potential.

How Do the Turbine Housings and A/R Ratios Compare?

The turbine housings and A/R ratios compare as follows: the HX35 commonly uses turbine A/R ratios between 0.60 and 0.80, favoring quicker spool at the cost of top-end exhaust flow. The HX40 offers larger A/R options, often ranging from 0.76 to 1.15, which delays spool slightly but supports higher sustained power. The HE351's turbine housing sits between these two in exhaust flow capacity, with A/R ratios typically near the HX35 range but paired with a more efficient turbine wheel profile. A/R ratio selection directly determines the balance between low-end response and peak power, so matching it to your engine's displacement and RPM range is critical.

How Do the Overall Dimensions and Mounting Differ?

The overall dimensions and mounting differ based on each turbo's generation and intended application. The HX35 and HX40 share a similar pedestal-style mounting flange, often making physical swaps between them straightforward on Cummins platforms. The HX40 is noticeably larger in overall length and turbine-side bulk, which can create clearance issues in tighter engine bays. The HE351, a newer-generation design, uses a different mounting footprint with an integrated actuator provision on VGT variants. Downpipe and exhaust manifold bolt patterns may not interchange directly between the HX/HE families without adapters.

With size and fitment differences clarified, airflow capacity reveals how each turbo performs under load.

How Does Airflow and Power Capacity Differ Between Them?

Airflow and power capacity differ between the HX35, HX40, and HE351 based on compressor size, turbine geometry, and intended engine displacement. Each turbo supports a distinct horsepower range.

What Horsepower Range Does the HX35 Support?

The HX35 supports a horsepower range of approximately 300 to 450 hp. Its 54mm to 58mm compressor wheel delivers sufficient airflow for mid-range diesel engines, particularly the 5.9L Cummins found in Dodge Ram pickups. At the lower end, the HX35 provides strong boost response for stock or lightly modified engines. Tuned applications with fueling upgrades can push the turbo toward its upper efficiency limit near 450 hp, though sustained operation at that ceiling accelerates shaft speed beyond optimal levels. For builds targeting reliable daily output between 325 and 400 hp, the HX35 remains one of the most proven choices in its displacement class.

What Horsepower Range Does the HX40 Support?

The HX40 supports a horsepower range of approximately 400 to 600 hp. Its larger 60mm to 62mm compressor wheel moves significantly more air volume than the HX35, making it suited for higher-displacement or heavily fueled diesel engines. Industrial and on-highway applications using 8.3L to 15L Cummins engines rely on the HX40 for sustained high-output operation. Performance builds targeting 500 hp or more benefit from the HX40's broader compressor map, which maintains efficiency at elevated boost pressures where the HX35 would surge. The trade-off is slower spool-up at low RPM, a compromise that matters less in engines with enough displacement to generate adequate exhaust energy.

What Horsepower Range Does the HE351 Support?

The HE351 supports a horsepower range of approximately 325 to 500 hp. Holset designed the HE351 platform with a smaller, lighter rotating assembly compared to the HX series, enabling faster transient response while still flowing enough air for moderate power levels. The HE351CW and HE351VE variants equipped on 6.7L Cummins ISB engines use variable geometry or wastegate control to optimize boost delivery across the full RPM band. This makes the HE351 particularly effective for applications that demand both low-end responsiveness and mid-range power, sitting between the HX35's compact efficiency and the HX40's high-flow ceiling.

With power capacity established, spool-up behavior further separates these three turbos.

How Does Spool-Up and Turbo Response Compare?

Spool-up and turbo response compare differently across the HX35, HX40, and HE351 due to variations in wheel size, housing volume, and inertia. Below, each turbo's low-RPM spool characteristics and top-end airflow capacity are examined.

Which Turbo Spools Fastest at Low RPM?

The HE351 spools fastest at low RPM. Its smaller compressor wheel and lighter rotating assembly reduce rotational inertia, allowing exhaust gases to accelerate the turbine more quickly from idle and low-speed driving conditions. The HX35, with its compact 54–56 mm compressor wheel, follows closely and delivers noticeably quicker response than the HX40. Because the HX40 uses larger compressor and turbine wheels, it requires more exhaust energy before reaching effective boost pressure, resulting in the slowest spool of the three.

For daily driving, towing, and applications that demand immediate throttle response at low engine speeds, the HE351 and HX35 hold a clear advantage. The HX40's slower spool becomes less of an issue once engine RPM climbs into the mid-range, but drivers consistently notice the lag during low-RPM acceleration.

Which Turbo Delivers the Best Top-End Airflow?

The HX40 delivers the best top-end airflow. Its larger compressor wheel, typically 60–62 mm, moves a significantly higher volume of air at elevated RPM compared to the HX35 and HE351. This greater airflow capacity supports higher peak horsepower, making the HX40 the preferred choice for performance builds and heavy-duty applications that operate consistently at higher engine speeds.

The HX35 and HE351, while efficient within their designed power bands, reach their airflow limits sooner. Pushing either turbo beyond its intended capacity risks compressor surge and reduced efficiency. The trade-off is straightforward: faster spool sacrifices top-end volume, while greater top-end airflow requires more exhaust energy to reach full boost. Matching the turbo to the engine's operating range is the single most important factor in achieving reliable performance.

Understanding spool behavior helps narrow down which Holset turbo fits specific driving and work demands.

What Are the Best Applications for Each Turbo?

The best applications for each turbo depend on engine displacement, power goals, and duty cycle. The HX35 and HE351 suit lighter-duty needs, while the HX40 handles higher-demand scenarios.

Which Turbo Is Best for Daily Driving and Towing?

The best turbo for daily driving and towing is the HE351. Its variable geometry technology (in VGT variants like the HE351VE) delivers quick spool-up at low RPM while maintaining sufficient airflow for loaded highway cruising. For trucks pulling trailers in the 5,000 to 12,000-pound range, this balance between low-end response and mid-range power makes the HE351 the most practical choice.

The HX35 also performs well for daily drivers who tow lighter loads. Its fixed-geometry design is simpler and offers reliable boost response in the low-to-mid RPM band where most street driving occurs. For owners prioritizing drivability over peak power, either turbo keeps exhaust gas temperatures manageable during sustained towing.

Which Turbo Is Best for Performance and Racing?

The best turbo for performance and racing is the HX40. Its larger compressor wheel and higher airflow capacity support power levels that the HX35 and HE351 cannot sustain. Sled pulling, drag racing, and dyno competition builds benefit from the HX40's ability to move enough air for 500-plus horsepower setups when paired with supporting fuel system upgrades.

The trade-off is slower spool-up compared to the smaller turbos, which makes the HX40 less responsive at low RPM. Competitors often pair it with larger injectors, a performance exhaust manifold, and tuning calibration to keep the turbo in its efficient operating range. For builds prioritizing peak output over street manners, the HX40 remains the go-to Holset platform.

Which Turbo Is Best for Heavy Equipment and Industrial Use?

The best turbo for heavy equipment and industrial use is the HX40. Engines in excavators, loaders, and generator sets typically operate at sustained high loads where consistent airflow at elevated RPM matters more than transient response. The HX40's larger turbine housing and higher A/R ratios match these steady-state duty cycles. According to a 2004 Federal Register rule published by the U.S. Government Publishing Office, Tier 4 standards for nonroad diesel engines require manufacturers to determine which emission control technologies meet compliance requirements. Industrial operators should verify that any turbocharger replacement aligns with applicable emissions regulations for their equipment class and model year.

Which Turbo Is Best for Agricultural Applications?

The best turbo for agricultural applications is the HX35 or HX40, depending on engine size and load profile. Smaller agricultural diesels in the 4- to 6-liter range pair naturally with the HX35, which provides adequate boost without oversizing the turbo for the engine's volumetric flow. Larger agricultural engines powering combines, high-horsepower tractors, and irrigation pumps benefit from the HX40's greater airflow capacity.

Agricultural equipment cycles between idle, partial load, and full load more frequently than highway trucks. Selecting a turbo sized correctly for the engine's displacement ensures the compressor operates within its efficiency island across these varying conditions, reducing exhaust gas temperatures and extending turbo life.

With each application matched to the right turbo, the next consideration is whether these three Holset models can physically swap for one another.

Can You Swap an HX35, HX40, or HE351 for Each Other?

Yes, you can swap an HX35, HX40, or HE351 for each other in many cases, but each swap requires specific modifications. The extent of work depends on mounting differences, plumbing compatibility, and emissions compliance.

What Modifications Are Needed to Swap an HX35 for an HX40?

The modifications needed to swap an HX35 for an HX40 center on the exhaust housing and downpipe. The HX40 uses a larger turbine housing with a different outlet flange, so the downpipe typically requires a custom adapter or full replacement. The compressor discharge piping may also need resizing to accommodate the HX40's larger compressor cover. Pedestal adapters are sometimes necessary because the HX40's footprint differs slightly from the HX35's mounting arrangement. Fuel system tuning is strongly recommended; the HX40 flows significantly more air, and without increased fueling, the engine will run lean under boost. For emissions-controlled vehicles, note that the U.S. EPA prohibits manufacturing, selling, or installing aftermarket devices that defeat emissions controls under the Clean Air Act.

What Modifications Are Needed to Swap an HX35 for an HE351?

The modifications needed to swap an HX35 for an HE351 are more involved because the HE351 is a fundamentally different platform. The HE351 uses a different compressor housing design and often incorporates a wastegate actuator integrated into the turbine housing, which changes the exhaust manifold interface. Adapter plates or a different exhaust manifold are usually required. The oil drain location and angle differ between the two platforms, so a custom oil drain tube or modified oil return bung is common. Electronic connections for the wastegate controller must also be addressed if upgrading from a non-electronic HX35 setup. These swaps demand careful planning, and working with a knowledgeable diesel parts supplier simplifies sourcing the correct adapters and gaskets.

Are the Oil and Coolant Lines Interchangeable?

The oil and coolant lines are not fully interchangeable across the HX35, HX40, and HE351. Oil feed fittings on the HX35 and HX40 often share the same thread size, making the oil supply line a straightforward match between those two models. The oil drain flange dimensions can vary, particularly when moving to or from an HE351, which may use a different bolt pattern or gasket surface. Coolant line compatibility depends on whether the specific turbo variant is water-cooled; not all HX35 and HX40 units include coolant ports. When coolant passages are present, fitting sizes and port locations differ enough between platforms that reusing existing lines without modification is unlikely.

Understanding swap compatibility helps narrow down which parts, adapters, and lines your specific build requires.

What Are Common Part Numbers for Each Holset Turbo?

Common part numbers for each Holset turbo identify specific configurations of compressor wheel, turbine wheel, and housing matched to particular engine applications. Below are the most referenced part numbers for the HX35, HX40, and HE351.

What Are the Most Common HX35 Part Numbers?

The most common HX35 part numbers correspond to Cummins 5.9L applications found in Dodge Ram trucks and midrange industrial engines. Frequently referenced numbers include:

• 3539373 - HX35W for 1996–1998 Dodge Ram 5.9L 12-valve Cummins

• 3539369 - HX35W for 1994–1995 Dodge Ram 5.9L 12-valve Cummins

• 3592766 - HX35W for 1999–2002 Dodge Ram 5.9L 24-valve Cummins (auto transmission)

• 3592767 - HX35W for 1999–2002 Dodge Ram 5.9L 24-valve Cummins (manual transmission)

• 3802841 - HX35 for Cummins 6BT industrial and marine applications

The "W" suffix indicates a wastegated version. When sourcing HX35 turbos by part number, working with a diesel parts supplier that verifies OEM specifications helps ensure you receive the correct configuration for your Cummins application.

What Are the Most Common HX40 Part Numbers?

The most common HX40 part numbers serve larger-displacement Cummins engines in heavy truck, construction, and industrial platforms. Key numbers include:

• 3591021 - HX40W for Cummins 8.3L 6CT/6CTA engines

• 3538215 - HX40 for Cummins ISC/ISL 8.3L–8.9L applications

• 4035235 - HX40W for Cummins QSL9 industrial engines

• 3597311 - HX40 for Cummins ISM 10.8L engines

• 4029184 - HX40 for Cummins 6CT marine and generator sets

Because the HX40 spans a wide horsepower range, confirming the exact part number matters. Turbine housing A/R and compressor inducer diameter vary significantly between numbers, even within the same model family.

What Are the Most Common HE351 Part Numbers?

The most common HE351 part numbers serve the Cummins ISB 5.9L and 6.7L engines used in 2004-and-later Dodge Ram trucks and medium-duty commercial vehicles. Widely referenced numbers include:

• 4043600 - HE351CW for 2004.5–2007 Dodge Ram 5.9L Cummins ISB

• 4955908 - HE351VE (VGT) for 2007.5–2012 Dodge Ram 6.7L Cummins ISB

• 2882111 - HE351VE (VGT) for 2013–2018 Dodge Ram 6.7L Cummins ISB

• 5325950 - HE351CW for Cummins ISB 5.9L medium-duty truck applications

• 4352378 - HE351VE for Cummins ISB 6.7L industrial/vocational platforms

The HE351VE numbers feature variable geometry turbine vanes, a significant distinction from the fixed-geometry HE351CW. Matching the correct part number determines whether the turbo uses VGT or wastegate boost control, which affects both performance and ECM compatibility.

With specific part numbers identified, selecting the right configuration becomes the final step in matching a Holset turbo to your build.

How Do You Choose the Right Holset Turbo for Your Build?

You choose the right Holset turbo by matching compressor and turbine sizing to your engine displacement, horsepower target, and intended use. The following sections cover how Goldfarb & Associates can help and what to keep in mind about the HX35, HX40, and HE351.

Can Goldfarb & Associates Help You Find the Right Turbo?

Yes, Goldfarb & Associates can help you find the right turbo. As America's leading diesel parts supplier since 1997, Goldfarb & Associates stocks over 20,000 unique part numbers, including new, used, and remanufactured diesel parts and turbochargers such as the HX35, HX40, and HE351 Every turbocharger undergoes a thorough hand inspection and must pass a full quality checklist before shipping. Goldfarb & Associates offers knowledgeable staff who can identify the correct turbo by engine application, part number, or build goals. Orders placed Monday through Friday before 3:30 PM EST ship same day. For sizing guidance or hard-to-find Holset turbos, contact Goldfarb & Associates at 301-770-4514.

What Should You Remember About the HX35, HX40, and HE351?

The key things you should remember about the HX35, HX40, and HE351 are their distinct strengths across different power ranges and applications:

• The HX35 delivers fast spool-up and reliable boost for daily driving, towing, and mid-range horsepower builds on engines like the Cummins 5.9L.

• The HX40 supports higher airflow capacity for performance builds, racing applications, and larger displacement engines that demand sustained top-end power.

• The HE351 combines electronic wastegate control with responsive spool characteristics, making it the factory choice on modern 6.7L Cummins platforms for both drivability and emissions compliance.

Selecting among them comes down to matching compressor sizing, turbine A/R ratio, and spool characteristics to your specific engine, power target, and driving style. With the right turbo matched to your build, diesel performance improves across the entire power band.