How to find out the maximum engine speed

What is engine torque?

Car enthusiasts are well aware of the concept of engine power and that it is measured in “horsepower” (hp or simply “horses” and even “mares”).
They understand perfectly well that 100 horses is perfect for a small hatchback, but of course it will not be enough for something larger and heavier, for example, a sedan or SUV. Well, 600 horses is certainly too much for any car. The main indicator of an engine is power.
Power shows how strong the motor is. But the power, or rather the power reserve of the engine, directly depends on the speed. When the engine speed is 6,000 i.e. at medium speeds, a modern engine will produce the most power, but we don’t drive around the city at such speeds. For city driving, approximately 3,000 rpm on our tachometer is sufficient. It turns out that if the engine of our car produces approximately 100 horses at maximum speed, and if we move in the city at medium speeds, we will have 50 horses in reserve.

Examples[ | ]

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On gramophone records, the speed is indicated in revolutions per minute (rpm). The standard uses 16+2⁄3, 33+1⁄3, 45 or 78 rpm (5⁄18, 5⁄9, 3⁄4, or 1.3 rpm, respectively).
Modern dental drills have rotation speeds of up to 800,000 rpm (13,300 rpm).
The second hand of a watch rotates at a frequency of 1 rpm.
CD players read at a speed of 150 kB/s - and the rotation speed of the disk when reading closer to the center is approximately 500 rpm (8 rps), and at the outer edge - 200 rpm (3.5 rpm). With). CD drives operate at speeds that are multiples of these numbers, even when using variable read speed.
DVD players typically read discs at a constant linear speed. And the rotation speed varies from 1530 rpm (25.5 rps) when reading at the inner edge to 630 rpm (10.5 rps) on the outer side of the disk.[2] Also, DVD drives can start at speeds that are multiples of the above numbers.
During the spin cycle, the rotation speed of the washing machine drum can range from 500 to 2000 rpm (8–33 rpm).
The TPP generator turbine rotates at 3000 rpm (50 rps) or 3600 rpm (60 rps), depending on the country (see AC frequency standards). The generator shaft of a hydroelectric power station can rotate more slowly: up to 2 rps (in this case, the network frequency of 50 Hz is obtained due to the presence of a larger number of poles of the stator coils).
A passenger car engine usually operates at a rotation speed of 2500 rpm (41 rpm), at idle speed - about 1000 rpm (16 rpm), and maximum speed - 6000-10,000 rpm ( 100-166 rps).
An airplane propeller typically rotates at speeds between 2000 and 3000 rpm (30-50 rps).
A computer hard drive with ATA or SATA interfaces rotates at 5400 or 7200 rpm (90 or 120 rpm), and very rarely at 10,000 rpm. Server hard drives with SCSI and SAS interfaces use speeds of 10,000 or 15,000 rpm (160 or 250 rpm).
The engine of a Formula 1 car can develop 18,000 rpm (300 rps) (according to the regulations for the 2009 season).
A uranium enrichment centrifuge rotates at 90,000 rpm (1500 rps) or faster.[3].
A gas turbine engine rotates at tens of thousands of revolutions per minute. Model airplane turbines can accelerate to 100,000 rpm (1,700 rpm), and the fastest ones can reach 165,000 rpm (2,750 rpm)[4].
A typical 80mm computer fan spins at 800-3000 RPM and is powered by 12 DC.
The turbocharger can reach a speed of 290,000 rpm (4800 rpm), and during quiet driving 80,000–200,000 rpm (1000–3000 rpm) are used.
To simulate human-comfortable gravity, which would be similar to Earth's gravity, the rotation speed of the space station (such as the Stanford torus) should be 2 rpm or less to reduce the effect of motion sickness (this is caused by the Coriolis force).

Torque, what is it and why is it needed?

Each internal combustion engine is designed to produce a certain maximum power that it can produce at a certain number of crankshaft revolutions. However, in addition to maximum power, there is also such a value in the engine characteristics as maximum torque, achieved at speeds other than maximum power speed.

What does the concept of torque mean?

Scientifically speaking, torque is equal to the product of force and the arm of its application and is measured in Newton meters. This means that if we apply a force of 1 Newton (perpendicular to the end of the wrench) to a wrench 1 meter long (arm), we will obtain a torque equal to 1 Nm.

For clarity. If the nut is tightened with a force of 3 kgf, then to unscrew it you will have to apply a force of 3 kg to a wrench with an arm length of 1 meter. However, if you put an additional 2-meter piece of pipe on a 1-meter long wrench, thereby increasing the lever to 3 meters, then to unscrew this nut you will only need a force of 1 kg. This is what many car enthusiasts do when unscrewing wheel bolts: either they add a piece of pipe, and in the absence of one, they simply press the key with their foot, thereby increasing the force applied to the wheel key.

Speed and revolutions: fuel savings and engine life

So, you can often hear from drivers that as soon as the car accelerates to 60 km/h, you can engage, for example, 5th gear (if the gearbox is 5-speed). In this case, the speed will drop to 1900-2000 thousand rpm and in this mode fuel consumption will be minimal. In other words, the most economical option is to drive when the highest gear is engaged and the speed is low.

If you study the theoretical part a little, accelerating to a certain speed will require energy expenditure. The more intense the acceleration occurs, the more energy is consumed. After reaching a constant speed (cruising), fuel consumption becomes less, but it must be taken into account that the car also overcomes air resistance.

Without going into mathematical calculations, an increase in speed, for example, from 50 km/h to 100 km/h will mean that air resistance increases not by 2 times, as many might think, but by as much as 8 times. That is, to maintain the current speed, you will need to expend 8 times more energy. It is to overcome air resistance that engine power is expended.

It turns out that to maintain a speed of about 50 km/h, you need about 30-35 hp, while when accelerating to 120-130 km/h, 80-90 “horses” are needed to overcome resistance to air flows. To this you need to add the mass of the car itself, which is different for each vehicle, make allowances for road conditions, etc.

You also need to remember that piston internal combustion engines demonstrate the best efficiency in the zone of maximum torque, and not maximum speed. At the same time, it should be taken into account that the gearboxes are also different and have different gear ratios.

It becomes clear that the most economical mode is actually achieved when the car is moving in top gear at a low speed, but the optimal speed in such a gear will be different for each car.

Another important point is, let’s say, the feasibility of saving fuel in this way. In the manual, many car manufacturers specifically indicate that you need to switch to the highest gears not at 50, but at 80 or even 100 km/h. The fact is that the lower the engine speed, the more the consumption drops, however, such driving at low speeds and in high gears can harm the engine.

For example, a 2.0 liter engine in a car weighing about 2 tons, which is moving in high gear at a speed of about 60 mph, will operate at low speed. In this case, the load on the motor will be very large. The fact is that the oil pressure at low speeds is also low, that is, the wear of parts and components of the power unit is maximum.

To reduce the load, you need to either add speed and increase the speed, or switch to a lower gear. If a car with the same engine weighs, for example, 1.3 tons, the load on the internal combustion engine will be less than in the case of a two-ton car, but accelerated engine wear will still be present.

If we summarize the information received, then it becomes clear that the lower the speed and the higher the gear, the lower the fuel consumption. At the same time, driving at low speeds “kills” the engine. This results in very dubious savings on fuel, which in no way covers the costs of engine repairs in the future.

Optimal engine speed.

Every driver should know what speed is optimal for the engine of his car, this knowledge will not only help save some money on fuel and repairs, but possibly also save a life, because without knowing the capabilities of your car, without knowing how to use its engine, you can put yourself in danger and its passengers.

Let's start with the fact that there are no universal speeds for all operating modes

. To warm up the engine, certain revolutions are required, for overtaking others, and for measured movement around the city, others.

Let's start with, of course, starting the engine, immediately after turning the key, the engine starts running at higher speeds (compared to idling). In this situation, this is the optimal speed for warming up the engine.

(usually 1100-1200 rpm), to supply frozen oil and thermal expansion of the connecting rod and piston group to the working size (you can read more here). If you want to extend the service life of your engine, you should not try to get rid of them, reflash the ECU, apply gas to warm up faster, but it is not recommended to start driving at warm-up speeds.

How to achieve fuel efficiency without harming the engine

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First of all, you need to determine at what speed in each gear the engine speed on a particular vehicle drops below 1800-2000 rpm. As a rule, for most engines, 1.8-2 thousand revolutions are the “minimum” when the pressure in the lubrication system is already sufficient to avoid increased wear.

Secondly, you must take into account road conditions. For example, a car moves at a speed of 60 km/h in 5th gear on a flat road, but then it begins to rise. The driver can either press the gas harder to maintain the speed, or shift to a lower gear.

So, in the first case, the load on the engine will be very large, and there is also a risk of detonation. At the same time, there is no longer any fuel economy, since you have to press the gas harder to maintain the selected speed. It turns out that the gasoline in the cylinders burns more intensely, and there is no traction in high gear, while the car overcomes the climb with great difficulty.

If you study the basic recommendations of experts regarding what revolutions, speed, gears and other factors affect fuel consumption and the life of the internal combustion engine, then for gasoline engines the following can be distinguished:

It is extremely undesirable to constantly drive at speeds below 2000 thousand;
it is necessary to select the gear in accordance with the road conditions;
movement in the highest gear should occur at optimal speed;

As for diesel engines, the optimal speed, speed and gear selection will differ from their gasoline counterparts. For this reason, the subtleties and features of economical driving on a diesel engine should be studied separately.

It should also be noted that to save fuel it is very important to learn how to maintain inertia. In practice, this means that you should not use the brake unless necessary, be able to use engine braking, change gears in a timely manner, taking turns with minimal loss of previously gained speed, etc.

We also recommend reading the article about what engine speed is best to drive at. From this article you will learn about what engine speed can be considered optimal for everyday use of a car.

Please note that such driving requires an understanding of all the processes taking place, that is, an inexperienced driver first needs some professional training (contingency driving), only after which can the acquired knowledge be applied in practice!

Calculation of engine power: methods and necessary formulas

Engine power is the energy that is generated inside the internal combustion engine during its operation. This indicator is key for any car, and many motorists rely on it when choosing a car. It can be defined in various ways. Let's list the main methods:

Through revolutions and torque.
By volume of internal combustion engine.
By air flow.
In terms of weight and acceleration time to 100 kilometers per hour.
According to the performance of injection nozzles.

The main unit of measurement for power is watts, but it is sometimes expressed in terms of horsepower. There is a simple relationship between these units of measurement, so if necessary, horsepower can be easily converted to watts (and vice versa).

In our article, we will look at the basic formulas for determining power, and also learn how to convert horsepower to watts.

Calculation formulas for electric motors

Calculation formulas for electric motors
Current in the stator of a three-phase electric motor at rated load, and

where P n is the rated power of the electric motor, kW, η is the efficiency of the electric motor, cos φ is the power factor, U is the voltage at the motor terminals, V.

Synchronous motor speed

where p is the number of pole pairs of the stator winding of the electric motor, f is the frequency.

Rated speed of an asynchronous electric motor

Slip of an asynchronous electric motor, %

Nominal torque of the electric motor, kg m

where D is the pulley diameter, m; F - force transmitted by the belt, kg.

Amount of heat generated by the electric motor in 1 second, kcal/sec

Where

kW - the amount of losses in the electric motor.

Peripheral speed (pulley, shaft, commutator, rotor), m/sec.

where D is the diameter of the corresponding machine element, m.

Efficiency coefficient (efficiency) of an asynchronous electric motor when speed is controlled by a rheostat in the rotor circuit

where p reg is the reduced engine speed per minute;

η reg - efficiency at reduced speed.

Relationships between work units

Relationships between power units

Calculation via torque

This method of counting is the main one. To measure power, you need to know two technical parameters - torque and engine speed. Therefore, the calculation is carried out in two stages.

What is torque

Torque is the force that acts on a rigid body during rotation. The higher this indicator, the more powerful the engine of your vehicle will be. The following formula is used to calculate torque:

The formula is deciphered as follows:

KM is torque.
O is the total engine volume, expressed in liters.
D is the pressure in the combustion chamber, expressed in MPa.
0.0126 is the correction factor.

How are engine speeds calculated?

To calculate operating power, we need not only torque, but also engine speed. In simple terms, RPM is the speed at which the engine crankshaft rotates. The relationship here is also direct - the higher the rotation speed, the more powerful and productive your car will be.

Calculation of power by engine volume

The attentive reader probably noticed that the first formula can be directly substituted into the second to simplify the calculations. The power in this case can be expressed as follows:

M = (KM x OD)/9549 = (O x D x OD)/(9549 x 0.0126) = (O x D x OD)/120.3.

The decoding of this formula will be standard:

O - engine volume.
D is the pressure in the combustion chamber.
OD - revolutions.
120.3 is the new correction factor.

Please note that the pressure in the combustion chamber (variable D) in the case of a standard gasoline engine is usually in the range from 0.8 to 0.85 MPa . In the case of a reinforced forced engine, this figure will be 0.9 MPa , in the case of a diesel engine - from 1 to 2 MPa .

Air flow calculation

If your car is equipped with an on-board computer and auxiliary sensors, then the power can also be determined by air consumption.

This is done as follows:

Place your car on the platform for tire fitting work, securely fix the car, and check the quality of the fixation.
Turn on the engine and accelerate the car to 5.5-6 thousand rpm . Determine air consumption using the on-board computer.
Calculate the final power using the following formula: M = PB x 0.243 . RV is the air flow rate, and 0.243 is the correction factor.

Photo of electric motor speed

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Calculation of weight and acceleration time from zero to hundreds

You can also determine how engine power is measured by the total weight of the car and the time it takes to accelerate to 100 kilometers per hour. Unfortunately, this method has one major drawback - the final formula is quite complex and it can vary greatly depending on the technical features of the car (type of drive, nature of the transmission, and so on).

Therefore, we recommend that you calculate power by weight and acceleration time not manually, but using a ready-made calculator on our website.

Optimal algorithm of actions:

Accelerate your car from 0 to 100 kilometers per hour. Determine the acceleration time in any convenient way (usually this is done using the on-board computer).
Find out the weight of your car - you can do this using the same on-board computer, using technical documentation, and so on.
Use our calculator - enter the mass and acceleration time, select the drive type, specify the transmission.

Calculation of injector performance

Injectors are spray parts that supply fuel to the cylinders of the internal combustion engine. The nature of the injectors’ operation directly affects the engine’s operating format, so the engine power can be calculated based on the performance of the injectors.

The following complex formula is used for calculations:

PF is the performance of 1 injector. This parameter is usually indicated in the technical documentation for the engine (although in the case of a new car, this information can be found from the on-board computer).
KF is the number of injectors. This parameter can also be found from the technical documentation or using the on-board computer.
KZ - injector load factor. For most passenger cars this parameter is equal to 0,75-0,8.
TT - type of fuel mixture. For highly purified gasoline, this coefficient is usually 12-13.
TD is a type of engine. For an atmospheric engine this parameter is 0.4-0.5, for a turbo engine - 0.6-0.7.

This calculation method is quite inaccurate, since the formula contains many correction factors, many of which do not have an exact digital expression. Therefore, the real power may differ from the formula power by 10-15% (however, this is a small error).

Horsepower calculation

If you know the amount of horsepower of your engine, then you can easily find out and calculate the engine power. A simple formula is used to calculate:

It deciphers like this:

M(LS) - power of an internal combustion engine, expressed in horsepower.
0.735 is a correction factor by which you need to multiply the number of your “horses”.