How to Decode a Holset Turbocharger Part Number: Full Reference Guide

Learning How to Decode a Holset Turbocharger Part Number is one of the most useful skills a diesel mechanic or fleet manager can pick up, because the numbers stamped on that housing tell you exactly what you’re working with before you ever pull the unit off the engine. Holset, the turbo brand of Cummins Turbo Technologies (the former Holset company, part of Cummins since 1973), has produced millions of turbos across the HX, HE, HY, and WH series, and every one of them carries a coded identity. Get fluent in that code and you can source the right replacement in minutes instead of guessing.

At PT Turbo we’ve been reading these numbers since 1978. Over 45+ years in business we’ve handled tens of thousands of Holset units across on-highway trucks, ag equipment, and marine applications. This guide breaks down the numbering system the way we teach it on the shop floor.

Where to Find the Holset Part Number

Holset turbos carry a stamped or laser-etched nameplate, usually riveted or attached to the compressor housing or the center bearing housing. On many units the numbers are also die-stamped directly into the compressor cover.

You’ll typically see two critical numbers: the HOL number (the assembly or part number) and the serial number. Don’t confuse them. The assembly number identifies the exact turbo build. The serial number is a unique production identifier for that individual unit.

• Assembly number: seven digits, e.g. 3599811 or 4043600.
• Serial number: alphanumeric, unique to the unit, used for warranty and traceability.
• Cummins CPL: found on the engine dataplate, cross-references the correct turbo build.

Always record both numbers before ordering. If the nameplate is missing or corroded, the casting numbers cast into the turbine and compressor housings become your fallback reference.

How to Decode a Holset Turbocharger Part Number: The Number Structure

Holset uses a sequential assembly numbering system rather than a fully descriptive code like some manufacturers. This trips people up, because a Holset assembly number, like a Garrett part number, does not spell out frame size and trim in the digits themselves.

Instead, the assembly number points to a specific documented build in the Cummins/Holset database. That build defines everything: compressor wheel, turbine wheel, housing A/R, actuator type, and calibration.

The three numbers you need to understand

1. The model designation. This is the family and frame, such as HX35W, HE351VE, HE300VG, or HX40. The letters and digits here DO carry meaning.

2. The Holset assembly (HOL) number. This seven-digit number identifies the complete turbo assembly, including its exact internal spec.

3. The revision or supersession suffix. Holset frequently supersedes older assembly numbers with updated builds. An older number may cross to a newer, improved unit.

Decoding the model designation letters

Code	Meaning
HX	Standard wastegated or fixed-geometry frame
HE	The newer H-series generation: wastegated (HE351CW) or variable geometry (HE351VE)
HY	Wastegated versions with a smaller turbine housing (HY35W on the Ram 5.9L)
WH	Wastegated H-series
Number (35, 40, 50, 55)	Approximate frame/turbine size
W	Wastegated variant
VE / VG	Variable geometry with an electronic actuator (a V on its own, as in HE551V, is air-operated)

So an HX35W is a 35-frame fixed geometry turbo with a wastegate, the classic unit on the 5.9L Cummins. An HE351VE is a 35-frame variable geometry turbo with electronic actuation. The frame number gives you a ballpark on airflow capacity, while the suffix tells you the actuation strategy.

If you’re working on any of these specific frames, we’ve published detailed application guides worth bookmarking: the Holset HX35 fitment guide, the HE351VE specs and replacement guide, and the HE300VG variable geometry operation guide.

Worked Example: Reading a Real Holset Number

Let’s take a common HX35W assembly number, 3592766. Here is how a tech at our bench breaks it down.

• Model: HX35W, a 35-frame wastegated turbo.
• Assembly number 3592766: points to the exact build spec, in this case a 1999 to 2002 Dodge Ram 5.9L 24-valve application with a manual transmission.
• Serial number: a unique per-unit code, irrelevant to spec but needed for warranty.

Now compare that to a variable geometry unit like the HE351VE used on the 2007.5-2012 6.7L Cummins. Same frame family, completely different actuation and internal geometry. The variable geometry design uses sliding nozzle vanes controlled by an electronic actuator, so the correct assembly number is critical, because the calibration is matched to the engine ECM.

This is why you never order a VGT turbo by frame size alone. Two HE351VE units with different assembly numbers can have different vane geometry and ECM calibration, and the wrong one will throw fault codes or cause boost control problems.

Actuators: The Detail That Sinks Most Orders

The single most common mistake we see is ordering a turbo or a replacement actuator that doesn’t match the calibration of the original. On both variable geometry and wastegated turbos, the actuator is calibrated to a specific build. Swap in the wrong one and boost control goes out the window.

While Holset uses electric actuators on most of its VGT units (early ones such as the HE551V are air-operated), plenty of the Garrett and Mitsubishi turbos we service alongside them use pneumatic actuators, and matching the right actuator to the turbo build is the same discipline.

The lesson carries straight back to Holset: always confirm the actuator part number and calibration against the original turbo assembly number, not just the frame.

Cross-Referencing and Supersessions

Holset regularly supersedes assembly numbers. An older number often crosses to a newer one with running changes to the wheel, seal package, or actuator. When you enter the original number in a Holset or Cummins parts system, it will flag the current supersession.

This matters for two reasons. First, the superseded unit is usually the improved version and is what you want. Second, if you order the obsolete number blindly from a reseller, you may get an outdated build with the very weakness that got it revised.

When the nameplate is gone, cross-reference by:

• Engine make, model, and displacement
• Cummins CPL number from the engine dataplate
• Casting numbers on the turbine and compressor housings
• Vehicle VIN for OEM applications

Not sure what you’re looking at? Send us photos of the nameplate and castings through our contact page and we’ll identify the exact build. We do this every day. Cummins Turbo Technologies supersedes part numbers over time, and cross-referencing correctly keeps you on the current one.

New vs Remanufactured: Choosing the Right Replacement

Once you’ve decoded the number and confirmed the correct build, you have a sourcing decision. Here’s how new and remanufactured Holset units stack up.

Factor	New OEM Holset	Remanufactured
Cost	Highest	Typically 30-50% less
Availability	Can have long lead times	Often in stock

Warranty and quality depend entirely on who does the reman. A properly rebuilt Holset uses new bearings, seals, and a balanced CHRA, and on a wastegated or VGT unit the actuator gets recalibrated to the original build. A cheap reman that skips balancing or reuses tired internals will fail early and take your boost control with it. Buy reman from a shop that documents what it replaces.

For most fleet and owner-operator work, a quality remanufactured unit built to the correct superseded assembly number is the smart call. You get the updated internal spec at a lower cost and without the lead time on a new OEM order. Reserve new OEM for warranty-sensitive jobs or applications where the exact factory calibration is non-negotiable.

Whichever route you take, the decoding work comes first. Confirm the assembly number, check the supersession, and match the actuator before you ever put money down. Get those three right and the new-versus-reman choice is just budget and timing.

Frequently Asked Questions

Where is the part number located on a Holset turbocharger?

The part number is typically stamped on the compressor housing or on a metal ID plate attached to the turbo body. It can also appear on the bearing housing depending on the model.

What do the HX, HE, HY, and WH series designations mean?

The letters give the generation or type of the turbo (and a W on the end means a wastegate); the number that follows (35, 40, 50, 55) gives the frame size.

Who manufactures Holset turbochargers today?

Holset turbochargers are made by Cummins Turbo Technologies, the former Holset company, which has been part of Cummins since 1973. Holset is still the brand name on the turbos.

Once you have identified your Holset unit, PT Turbo’s turbo rebuild service can rebuild it to spec.