Holset HX30 Turbocharger: Small Block Cummins B-Series Application Guide

The Holset HX30 Turbocharger is one of the most versatile fixed-geometry chargers Cummins ever bolted to a small block B-series engine, and it remains a go-to unit for 3.9L 4BT and early 5.9L 6BT applications where response and durability matter more than peak horsepower. If you run a bread truck, a repowered project, a marine 4BT, or a light industrial genset, odds are you have crossed paths with this compressor. This guide breaks down the HX30 by application, spec, failure mode, and replacement strategy so you can spec the right unit the first time.

At PT Turbo we have been rebuilding and supplying Holset units for over 45 years, and the HX30 is a charger our bench techs know cold. Below is the practical, real-world breakdown we give customers on the phone every week.

What the Holset HX30 Actually Is

The HX30 is a single-stage, fixed-geometry turbocharger built by Holset (now part of Cummins Turbo Technologies). It sits below the more common HX35 in the Holset family and is purpose-built for lower-displacement B-series engines and smaller industrial diesels.

Where the HX35 targets the full-size 5.9L 6BT in Dodge Ram trucks, the HX30 shines on the 3.9L 4BT four-cylinder and low-output 6BT variants. Its smaller compressor and turbine wheels spool faster, which is exactly what a 3.9L needs to avoid feeling laggy off idle.

If you want a refresher on how fixed-geometry turbos move air compared to variable-geometry designs, the turbocharger overview on Wikipedia is a solid primer.

Typical HX30 Specifications

Parameter	HX30 (typical)	HX35 (for reference)
Compressor inducer	~46 mm	~54 mm
Compressor exducer	~60 mm	~76 mm
Turbine wheel	~55-60 mm	~65-70 mm
Turbine housing A/R	0.83 to 12 cm² common	12 to 16 cm² common
Practical airflow ceiling	~250-350 HP	~350-450 HP
Best-fit engine	3.9L 4BT, low-output 6BT	5.9L 6BT

Exact wheel sizes and housing A/R vary by part number and application, so always verify the casting numbers on the unit you are replacing. Holset built dozens of HX30 variants for on-highway, marine, ag, and industrial use.

Small Block B-Series Applications

The HX30 was fitted across a wide spread of Cummins small-block installations. Knowing which family your engine belongs to tells you what compressor map and turbine housing you should be matching.

• 3.9L 4BT (four-cylinder): The classic HX30 home. Common in step vans, delivery trucks, shuttle buses, and thousands of 4BT swap projects. The small A/R turbine housing gives crisp low-end spool that suits the 3.9L’s limited displacement.
• 5.9L 6BT (low-output industrial/ag): Some lower-rated 6BT engines in equipment, gensets, and irrigation pumps ran the HX30 for tighter response where peak power was capped.
• Marine 4BT/6BT: Marine-rated small blocks frequently used HX30 chargers with specific housings and water-cooled provisions on certain variants.
• Repower and conversion builds: 4BT swaps into Jeeps, older pickups, and off-road rigs almost universally keep or upgrade to an HX30 because it wakes the engine up quickly.

If your project has grown into a 5.9L platform, our 5.9L Cummins turbocharger guide covering the HX35, HY35, and HE341VE will help you step up to the right unit.

Common Holset HX30 Turbocharger Failure Modes

The HX30 is a tough charger, but every turbo has a service life. Most failures come down to oil supply problems, foreign object damage, or worn journal bearings after high hours. Catch these early and you save the engine, not just the turbo.

Symptoms Ranked by Severity

Severity	Symptom	Likely Cause
Early warning	Slight whistle change, minor oil film in charge pipe	Seal wear, early shaft play
Moderate	Blue smoke on startup, rising oil consumption, sluggish spool	Worn seals, bearing wear, restricted drain
Serious	Loud grinding or siren noise, visible shaft wobble	Failed journal or thrust bearing
Catastrophic	Metal in intake, sudden power loss, oil dumping into intercooler	Wheel contact, shaft failure, FOD

Before condemning any HX30, check the basics. Restricted air filters, a clogged oil feed line, and coked oil drains kill more turbos than manufacturing defects ever will. A quick shaft-play check by hand tells you a lot: light radial movement is normal, but any contact between the wheel and housing means the bearings are gone.

Actuators and Wastegate Components

Many on-highway HX30 variants ran a wastegated turbine housing to control boost, and the pneumatic actuator is a common wear item. A leaking diaphragm or a seized actuator rod will cause overboost, underboost, or erratic boost that a boost gauge will reveal quickly.

When an actuator diaphragm splits, boost control goes out the window, and on a small block that shows up as sluggish spool or boost creep at cruise. Replacing the actuator is far cheaper than replacing the whole charger, so it pays to diagnose it correctly.

PT Turbo stocks pneumatic actuators across the Garrett and Mitsubishi ranges for turbos that use wastegated housings and matching actuator geometry. Depending on your unit and any hybrid setup, options include:

• Garrett Pneumatic Actuator 757979-5102, available from PT Turbo for $240.94 – view the Garrett Pneumatic Actuator 757979-5102 here.
• Garrett Pneumatic Actuator 445963-0040, a higher-capacity unit at $465.52 – view the Garrett Pneumatic Actuator 445963-0040 here.
• Mitsubishi TD03 Pneumatic Actuator 49S3118761 for smaller frame applications at $104.33 – view the Mitsubishi TD03 actuator here.
• Mitsubishi Pneumatic Actuator 4918918935, the budget-friendly option at $83.99 – view the Mitsubishi Pneumatic Actuator 4918918935 here.

Always match the actuator by rod length, mounting bracket, and boost preload spring rating. If you are unsure which actuator fits your housing, contact PT Turbo with your casting numbers and our techs will spec it for you.

New vs Remanufactured HX30: What to Buy

You have three paths when your HX30 gives up: buy new, buy remanufactured, or rebuild the core you already have. Each has a place depending on budget, downtime, and how original you need to stay.

Option	Typical cost	Best for	Notes
New Holset HX30	$650 to $1,100	Fleets wanting max service life	Full factory tolerances, longest warranty
Remanufactured HX30	$350 to $600	Best value for most owners	New CHRA components, balanced, tested
Rebuild your core	$250 to $450	Keeping original housings/casting numbers	Preserves matched housings, fast turnaround

A quality remanufactured unit is the sweet spot for most owner-operators. Our remanufactured turbochargers are torn down completely, fitted with new bearings, seals, and balanced rotating assemblies, then flow and balance tested before they ship.

If you want to keep your original housings, our turbocharger rebuild service restores your core to spec with a fast turnaround. You can also

Cross-Reference & Superseded Part Numbers

The turbochargers covered in this article match or supersede the following OEM and manufacturer part numbers. If you are searching by part number, these are the units stocked by PT Turbo for this application:

3539846H  •  3580573H  •  3590025H  •  3590027H  •  3590029H  •  3591890  •  3592016H  •  3592016HX  •  3592018H  •  3592020H  •  3592104H  •  3592108H  •  3592110H  •  3592117H  •  3592119H  •  3592122H  •  3592126H  •  3592128H  •  3592205H  •  3592207H  •  3592309H  •  3592312H  •  3592316H  •  3592773  •  3593408H  •  3593409H  •  3593410H  •  3596329H  •  3598273  •  3598483  •  4027065H  •  4030045  •  4030227H  •  4030269  •  4030273  •  4030715  •  4030720  •  4030736  •  4030747  •  4030757  •  4030763  •  4030767  •  4030780  •  4030782  •  4030784  •  4030786  •  4030793  •  4030806H  •  4030831  •  4030835  •  4030845  •  4030847H  •  4030858  •  4030861  •  4030870  •  4030877H  •  4030892  •  4030894H  •  4030914  •  4030915  •  4030916  •  4030918H  •  4030923  •  4030926H  •  4030930  •  4030935  •  4030945  •  4030963  •  4030967  •  4031254H  •  4031315  •  4031327  •  4031345H  •  4031381  •  4031435  •  4031461  •  4031488  •  4032006  •  4032029  •  4032046  •  4032219  •  4032238H  •  4032259  •  4032262  •  4032265  •  4032277  •  4032284  •  4032292  •  4032294H  •  4032304H  •  4032305  •  4032306  •  4032605H  •  4032664  •  4032706  •  4032721  •  4032739  •  4032769  •  4032869H  •  4032975  •  4033075H  •  4033294H  •  4033301H  •  4033321H  •  4033367H  •  4033397H  •  4033406H  •  4033776H  •  4033791H  •  4033983H  •  4033984H  •  4034013  •  4034055H  •  4034144H  •  4034145H  •  4034150H  •  4034256H  •  4034294H  •  4034320H  •  4034322H  •  4034356H  •  4034384H  •  4034387H  •  4034464H  •  4034499  •  4035465  •  4036469H  •  4036553  •  4037504  •  4038545  •  4038889  •  4039339H  •  4040080H  •  4040391  •  4042573  •  4042956H  •  4043168  •  4043564  •  4044633  •  4044721  •  4044722  •  4044830  •  4047073H  •  5324279H  •  5503312H  •  6454763H

Can’t find your number above? Contact PT Turbo — our team has been matching part numbers since 1978.