Holset 6628740 Turbocharger For Sinotruk National VI Natural Gas Engines: Boost Pressure Closed-Loop & Gas Injection Synergy

Natural gas engines certified to China National VI operate under a different combustion regime than diesel. Methane has a slower laminar flame speed, higher autoignition temperature, and a narrower flammability range. The turbocharger must therefore supply boost that is not only sufficient but precisely matched to the gas injection rate to avoid misfire, knock, and excessive NOx. The Holset 6628740 is engineered for Sinotruk National VI natural gas platforms, where it works in closed loop with the gas rail and ECM. Although the fuel delivery system differs from diesel common rail, the ECM's boost control logic shares the same core principle: target air mass, fuel pressure, and injection duration must remain synchronized. This article examines the 6628740 from a gas-engine boost control and thermal management perspective.

The 6628740 is a Holset turbocharger specified for Sinotruk National VI natural gas engines, commonly deployed in heavy-duty trucks and buses. Fitment is governed by engine serial number (ESN), original turbo number, and boost control configuration. National VI gas engines often use cooled EGR and a three-way catalyst, which imposes specific exhaust temperature and lambda requirements. The turbo must match the EGR strategy and catalyst light-off behavior. Before ordering, verify the wastegate or VGT actuator type, mounting flange, and oil line connections. A unit that physically bolts on may still have the wrong boost curve for the ECM's gas injection map.

Model Reference: 6628740

Brand: Holset

Engine Platform: Sinotruk National VI natural gas

Boost Control: Wastegate or VGT (verify by OEM number)

Turbine Housing: High-nickel alloy for elevated exhaust temperature

Compressor Wheel: Precision-machined aluminum alloy

Lubrication: Engine oil pressure feed; low-ash oil recommended to protect catalyst

Emissions Target: China National VI

These specifications reflect the thermal demands of natural gas combustion. Stoichiometric natural gas engines with EGR produce higher exhaust temperatures than diesel, especially during catalyst regeneration or high-load operation. The turbine wheel and housing must resist heat soak without warping. The compressor wheel is matched to the engine's volumetric efficiency and the gas injection strategy, which may be port injection or direct injection.

In a National VI natural gas engine, the ECM calculates the required gas injection duration from gas rail pressure, boost pressure, intake air temperature, and lambda target. The 6628740 must deliver the commanded boost quickly. If actual boost is lower than target, the ECM reduces gas flow to prevent rich misfire, which cuts torque and may set a P0299 underboost code. If actual boost is higher than target, the ECM may retard spark timing or reduce gas flow to avoid knock, raising exhaust temperature and reducing efficiency. This closed-loop strategy mirrors diesel common-rail boost control: target air mass, fuel pressure, and injection duration must remain synchronized. Fault codes P0234 or P0299 often indicate a boost deviation, not necessarily a failed turbo.

Natural gas engines run higher exhaust temperatures than diesel, particularly with stoichiometric combustion and cooled EGR. The 6628740 turbine wheel and bearing housing must withstand these cycles. If the oil return is restricted or the oil is degraded, the bearing can coke, leading to shaft play and seal failure. Oil ash can also poison the three-way catalyst if the turbo seals leak. Before replacing the turbo, check EGR cooler flow, catalyst backpressure, and gas injector condition. A restricted catalyst can raise exhaust backpressure, forcing the wastegate to operate outside its design parameters and mimicking turbo failure.

1.Does Holset 6628740 fit all Sinotruk National VI natural gas engines?
No. Verify ESN, original turbo number, and actuator type. Production revisions may alter wastegate or VGT configuration.

2.Can this turbocharger be used on a diesel engine?
No. It is calibrated for natural gas exhaust temperatures, boost curves, and lambda targets. Diesel applications require a different turbine and compressor match.

3.What causes low boost on the 6628740?
Common causes include a stuck-open wastegate, boost leak, restricted catalyst, EGR cooler blockage, or incorrect actuator preload.

4.Is electronic calibration required after installing the 6628740?
If the unit uses an electronic VGT actuator, yes. Mechanical wastegate units require physical preload adjustment only.

5.How does natural gas affect turbocharger longevity?
Higher exhaust temperature and oil ash are the main risks. Use low-ash oil, maintain oil changes, and ensure the oil return line is unrestricted.

6.What is the typical boost pressure for the 6628740?
Boost pressure depends on ECM calibration and engine rating. Always refer to OEM specifications and verify with a diagnostic tool under load.