Details
A 70kW B3.9 Engine Built Around Performance Curve FR94625
The Cummins 4BTA3.9-G11 is the largest engine in the 3.9L B-Series generator range that HekoPower lists. It is a four-cylinder, turbocharged and aftercooled diesel built by Dongfeng Cummins (DCEC), and it belongs to the 4BT generator family. At 1500 RPM it is rated at 70kW prime and 80kW standby. At 1800 RPM the figures rise to 80kW and 90kW.
We supply it as an engine assembly for generator builders, rental fleets and owners replacing a worn power unit. It is not a finished generator. That difference matters when you size alternators, radiators and protection, and it shapes much of what follows.
Tech Specs of Cummins 4BTA3.9-G11 Diesel Generator Engine
General Engine Data
Engine Model: Cummins 4BTA3.9-G11-70kw
Type: 4 Cylinders in Line, 4 Stroke Diesel
Displacement: 3.9 L
Bore * Stroke: 102 * 120
Net Weight: 350 Kg
Overall Dimension: 867mm*544mm*988mm
Key Performance Data
Rated Power/Standby Power(1500 rpm): 70 kW/93 HP, 80 kW/107 HP
Rated Power/Standby Power(1800 rpm): 80 kW/107 HP, 90 kW/120 HP
Rated Speed: 1500/1800 rpm
Low Idle Speed: 950-1050 rpm
Fuel Consumption @ Running: ≤ 244 g/kW.hr
More Technical Data
Aspiration: Turbocharged/Aftercooled
Fuel System: BYC A Pump/GAC Governor
Electrical System (Starter Motor/Alternator): 12V/24V
Lowest Starting Temp Without auxiliary system: -12℃
Cooling Method: Water cooled
Engine Cooling Fluid Volume: 8.3 L
Governor Type: Electronic, Regulation ≤5%
How the G11 Compares With Its Nearest Relatives
G11 or the 58kW G2?
The two engines look similar on paper. Both are 3.9L, turbocharged and aftercooled, with an electronic governor. The difference is rating and calibration.
At 1500 RPM, DCEC rates the 4BTA3.9-G2-A at 58kW prime and 64kW standby. The G11-A is rated at 70kW and 80kW. At 1800 RPM the gap is wider: 67kW for the G2-B against 80kW for the G11-B.
So the choice starts with your largest realistic load, not with the displacement. If your generator will rarely pass 55kW, the G2 may be the more economical match. If you expect sustained load near 60kW or more, the G11 leaves useful margin.
Same engine, different kVA labels
Look at generator sets built around this engine and the kVA figures do not agree. One catalogue lists 80kVA prime and 88kVA standby. Another lists 73kVA prime and 80kVA standby. A 60Hz set from a third maker is rated 85kVA prime and 94kVA standby.
The engine did not change. Differences like these usually come from the alternator, cooling and safety margin each builder chooses. This is why we quote the engine rating in kW and leave electrical ratings to the package designer.
1500 RPM or 1800 RPM
The 1500 RPM version suits 50Hz sets. The 1800 RPM version suits 60Hz sets. Both use the same basic engine, but they are not the same rating and should not be treated as a switch you can flip.
One detail is easy to overlook. The DCEC data shows higher exhaust gas temperature at 1500 RPM than at 1800 RPM. At standby load it reaches 548°C, against 405°C at 1800 RPM. At prime load the figures are 526°C and 393°C. Lower speed moves less air through the engine, so ventilation and exhaust routing deserve attention on 50Hz installations.
What the fuel figures show
The performance sheet gives fuel use at several loads for the 1500 RPM prime rating. At full 70kW the engine uses 17.6 litres per hour. At 75% load it uses 13.2 litres. At 50% it uses 9.1 litres. At 25% it drops to 5.3 litres.
Efficiency is best between half and full load, at about 208 to 214 g/kWh. At 25% load it worsens to 251 g/kWh. A 1,000 litre tank would last roughly 57 hours at full prime load, or about 75 hours at 75% load. These are test figures, so treat them as planning numbers, not guarantees.
Where the G11 Fits in Practice
A factory on an unreliable grid
Plants with frequent outages often need a generator that runs for days, not minutes. Under Cummins prime-power rules, average load should stay at or below 70% of the prime rating. For this engine that means planning around 49kW of average load, even though it can peak higher.
Hospital and commercial building standby
Standby ratings are meant for real outages. Cummins limits standby operation to 200 hours per year, with no overload capability. The 80kW standby figure is therefore a ceiling for emergencies, not a daily working rating.
Remote pumping and rental fleets
At 867 x 544 x 988mm and about 350kg, it is compact enough for skid-mounted sets and towable units. The starter is available in 12V and 24V versions, so check the battery and cable arrangement before ordering.
Maintenance and Replacement Tips
Checks that catch problems early
Record oil pressure from the first day. The normal range runs from about 207kPa at idle to 345kPa at rated speed. A slow downward drift tells you more than a single reading.
Keep the air intake honest. Restriction should stay near 3.7kPa with a clean element and should not pass 6.2kPa when dirty. Exhaust back pressure should stay under 10kPa, so check any new silencer or pipe run.
Valve lash on B-Series engines is commonly given as 0.25mm intake and 0.51mm exhaust, set cold. Confirm the figures against the manual for your serial number before adjusting.
Before replacing an older engine
As a replacement engine supplier, we start with the data plate. Photograph it and send us the engine serial number. We check the CPL and performance curve against what you plan to install. The DCEC sheet we work from lists the G11 under CPL 4562 and performance curve FR94625.
Then compare the physical interfaces: flywheel housing, drive-disc size, mounting feet, exhaust outlet, radiator position and wiring. A model name alone does not prove that a replacement will bolt in.
Coolant capacity is another trap. The 8.3 litre figure applies to the engine only. Your radiator and hoses add more, so size the filling quantity for the whole system.
Common Misconceptions Regarding the 4BTA3.9-G11
Misconception: 80kW means extra capacity every day
It does not. Standby power is for emergencies only. For regular work, size the generator against the 70kW prime rating.
Misconception: any 3.9L Cummins will do
The physical size is similar across the B3.9 family, but power ratings, governors and fuel systems differ. A 36kW engine cannot be tuned into a 70kW engine.
Misconception: light load is gentle on the engine
Long periods at little or no load can cause wet stacking, where unburned fuel and carbon build up in the exhaust. Cummins recommends regular loaded exercise, with test runs at no less than one-third of the nameplate rating.
The Rest of the B3.9-G Family
If the G11 is larger than you need, the lower-rated models in the same family may suit you better. The comparison above explains the step from the 58kW G2 to the G11. The links below take you to the smaller engines, each with its own rating and specifications.
Cummins B3.9-G Series, original products from Dongfeng Cummins Engine Plant (DCEC), Cummins Joint Venture Plant since 1986, 50% shareholding by Cummins USA. This series mainly includes 4B3.9-G1-24kw, 4B3.9-G2-24kw, 4BT3.9-G1-36kw, 4BT3.9-G2-36kw, 4BTA3.9-G2-50kw, 4BTA3.9-G2-58kw, 4BTA3.9-G11-70kw.In accordance with the criteria of Machinery Safety Directive 2006/42, movable elements such as distribution belts, fans, and parts that acquire high temperatures during operation, such as exhaust manifolds, have their respective safeguards. Before being delivered, the generator is thoroughly checked at the factory. Voltage, frequency, and load are all tested, as well as the appropriate operation of warnings and the influence of engine oil temperature on stop.
Frequently Asked Questions
What is the original genuine Cummins 4BTA3.9-G11 engine price?
Pricing fluctuates based on global steel costs and specific accessory configurations (e.g., radiator type, 12V vs 24V starting system). As a direct China Cummins 4BTA3.9-G11 supplier, HekoPower bypasses middleman markups. Contact our sales engineering team at sales@hekopower.com for a current FOB wholesale quote.
Can this engine run continuously at 80kW?
No. 80kW is the standby rating, designed strictly for emergency use during grid outages for a maximum of 1 hour per 12 hours of operation. For continuous 24/7 operation without grid backup, the load must not exceed the prime power rating of 70kW.
Does HekoPower export the complete engine assembly?
Yes. We are a licensed Cummins 70kW diesel engine exporter. The engine assembly is shipped on a fortified steel skid, fully shrink-wrapped, and coated in an anti-corrosion layer suitable for extended ocean freight. All export documentation, including origin certificates, is handled in-house.
