Read the power at the speed you work at
An engine’s power is always stated at a given speed. If an engine delivers 55 kW at 2,600 rpm, it will not deliver the same power when the application holds it at 1,500 rpm. So we start from the machine’s working speed and the power needed at that speed, plus a margin for starting and load peaks.
An example from the Rehlko range: the KDI 2504 M delivers 36.4 kW at 2,600 rpm. The KDI 2504 TM, built on the same 2.5 l block but with a turbocharger, delivers the same 36.4 kW straight at 1,500 rpm, the fixed speed of a 50 Hz generator. Both belong to the KDI platform.
Torque
Torque shows how well the engine pulls under load, especially at low speed. On machines with variable loads (excavators, loaders, tractors, chippers), high torque low down means the engine speed drops less when the load rises suddenly. Two engines with the same power can look very different here. The VM Motori R753 IE5 (3 cylinders, 2.2 l) and R754 ISE5 (4 cylinders, 3.0 l) both deliver 55 kW at 2,600 rpm, but the first peaks at 250 Nm at 1,800 rpm and the second at 310 Nm at 1,100 rpm.
Air or liquid cooling
With air cooling there is no radiator, water pump or coolant. The engine is simpler and easy to maintain, which is why you often find it on motor pumps, small generators, walking tractors and compressors. In the Rehlko range, the air-cooled KD series covers 3.3–7.4 kW with the KD15 singles and 13–18.8 kW with the KD 425-2 and KD 625-2 twins.
Liquid cooling keeps the operating temperature steadier, reduces noise and allows higher outputs. The Rehlko KDW series (2–4 cylinders, 11.5–17.9 kW) is chosen for its quiet running, and the KDI, VM Motori and FPT Industrial platforms are all liquid-cooled.
Naturally aspirated, turbo or turbo with aftercooler
Turbocharging pushes more air into the cylinders, so you get more torque and power from the same displacement. You can see it clearly on the Rehlko KSD 1403 series (3 cylinders, 1.4 l). All three versions deliver 18.9 kW at 3,000 rpm, but peak torque rises from 90 Nm (NA, naturally aspirated) to 105 Nm (TC, turbocharged) and 120 Nm (TCA, turbocharged and aftercooled). The aspirated engine has fewer components, the turbo engine gives you more torque in a smaller package.
Emission standards: Stage V, Tier 4 Final and others
Non-road mobile machinery (construction, agriculture, materials handling) placed on the market in the European Union must meet EU Stage V. The US equivalent is EPA Tier 4 Final. Between 19 and 560 kW, Stage V also limits the number of particles, which is why many engines in this class have a particulate filter, for example the VM Motori R753 IE5 and R754 ISE5 (DOC + DPF). Others meet the standard without a DPF: the Rehlko KDI 3404 TCR-SCR uses SCR after-treatment. Below 19 kW the requirements are simpler, and some compact engines, such as the KSD 1403, are rated just under the threshold, at 18.9 kW.
Engines certified to earlier standards (Stage IIIA, Stage II), VM Motori’s “Fuel Optimised” versions and FPT engines marked “unregulated” are for applications and markets where Stage V is not required. Before ordering, check which standard applies to your machine.
The application: generator, pump or machine
- Generator sets: the engine runs at a fixed speed, 1,500 rpm for 50 Hz or 1,800 rpm for 60 Hz. Output is given as standby (back-up during mains failures) and prime (continuous running with variable load). For example, the VM Motori D754 TPE2.GEN is rated 63/57 kVA standby/prime at 1,500 rpm, and the FPT G-Drive range runs from the R24 (22–38 kWm standby at 1,500 rpm) up to the Cursor 16 (557 kWm).
- Pumps and motor pumps: constant speed and continuous load. VM Motori supplies MTP versions ready-equipped with radiator, fan and starter motor, from 33 to 105 kW, and F3S and FRP versions for fire pumps.
- Mobile machinery: variable load, low-speed torque, compact size. This is where the Rehlko KDI platform (1.9–3.4 l, up to 105 kW on the KDI 3404 TCR-SCR), the VM Motori R750 common rail series and the FPT off-road range fit, from the F28 (37–75 kW) through the NEF and Cursor families up to the 670 kW V20.
When you ask us for a quote, it helps to know the application, the power and working speed, the emission standard required, the installation space and the coupling type (SAE flywheel housing, PTO). If you are replacing an engine, send us the model and serial number of the existing one too. From there we propose options from the Rehlko, VM Motori and FPT Industrial ranges.
