Ideal petrol and diesel engine speed

Optimum speed of the diesel engine

A diesel unit equipped with a turbocharger is on longer routes at a constant load probably the most economical choice. The earlier ones were not too complicated and they liked understeer, which unfortunately the dual-mass flywheels of modern engines do not tolerate. The effort to save can thus turn into an expensive service operation.

Of course, individual engines have a little different power and torque curvesthey are also not all the same size and the same controlled turbochargers. In general, however, we do not recommend driving permanently below 1200 rpm, which, after all, will show the aggregate itself strong vibrations passing through the entire body. The optimum can be found on some longer straights, where it is enough to engage the highest gear and then watch how the instantaneous consumption changes with the revolutions. Most diesel engines have a “sweet spot” somewhere in between 1500-2000 revolutions.

If you’re going uphill and you’re hesitating whether to downshift or leave it in fifth gear, it is better to leave the higher gear, if the car can handle it (it doesn’t have to accelerate, it’s enough when it doesn’t slow down). If it would be too much for the car, i.e. the engine, lower it sooner rather than later.

Optimum revolutions of the petrol engine

Here it is a little more complicated, because gasoline engines have gone through a dramatic development, mainly consisting in reducing the volume and number of cylinders. Nevertheless, we can only recommend a similar procedure as in the case of diesel – just try it. For older petrol units, the consumption is usually the lowest in the range 2000-2500 rpm in a minute.

The very latest engines, meeting the standard Euro 6d, they already work the vast majority of the time with a lean mixture. So it doesn’t make much sense to try for some gentle and very smooth acceleration. On the contrary, it is better to leave the intersection more briskly and get to the desired speed faster and then maintain it, rather than accelerating decently.

What about hybrids?

For full hybrid engines automatic transmission shifts, variator, possibly not listed there at all (typically Honda). The combustion engine and electric motor combination system is built for maximum efficiency and maximum fuel economy, so the driver cannot directly influence the revs there. They are maintained for him by a system that knows well when the engine is most efficient. Toyota can work well with this, where the engine often runs at a constant speed and the shifter takes care of smooth gear changes (e-CVT transmission), so the car accelerates. Some hybrid cars can be forced to the maximum Eco mode or some other way of preferring the battery over the incinerator, which will increase the efficiency a little more.