Car engine power calculator

Let's look at 5 popular methods how to calculate car engine power using data like:

engine speed,
engine volume,
torque,
effective pressure in the combustion chamber,
fuel consumption,
injector performance,
machine weight
acceleration time to 100 km.

Each of the formulas used to calculate the power of a car engine is quite relative and cannot determine with 100% accuracy the real horsepower of the driving car. But by making calculations for each of the above garage options, based on certain indicators, you can calculate at least the average value, whether it’s a stock or tuned engine, literally with a 10 percent error .

Power is the energy generated by the engine, it is converted into torque on the output shaft of the internal combustion engine. This is not a constant value. Next to the maximum power values, the speed at which it can be achieved is always indicated. The maximum point is reached at the highest average effective pressure in the cylinder (depending on the quality of filling with fresh fuel mixture, combustion completeness and heat losses). Modern engines produce the greatest power on average at 5500–6500 rpm. In the automotive industry, engine power is measured in horsepower. Therefore, since most results are displayed in kilowatts, you will need a kW to hp conversion calculator.

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.

Asynchronous motor

An asynchronous unit is a device whose peculiarity is that the rotational speed of the magnetic field created by its stator is always greater than the rotational speed of its rotor.

The operating principle of an asynchronous machine is similar to the operating principle of a transformer. The laws of electromagnetic induction are applied (the time-varying flux linkage of the winding induces an EMF in it) and Ampere (an electromagnetic force acts on a conductor of a certain length through which a current flows in a field with a certain induction value).

An asynchronous motor generally consists of a stator, rotor, shaft and support. The stator includes the following main components: winding, core, housing. The rotor consists of a core and a winding.

The main task of an asynchronous motor is to convert electrical energy, which is supplied to the stator winding, into mechanical energy, which can be removed from the rotating shaft.

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:

KM = (O x D)/0.0126

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.

To calculate power through revolutions, use the following formula:

M = (KM x OD)/9549

KM is torque (the formula for calculating it can be found in the previous paragraph).
RO - engine speed (expressed in revolutions per second).
9549 is the correction factor.

Please note that this formula is suitable for calculating the maximum engine power .

Unfortunately, during operation of the internal combustion engine, part of the power is “eaten up” by certain elements of the car (transmission, transfer case, air conditioning, and so on).

Therefore, in fact, the actual engine power indicator will be 10-15% less, depending on the type of car and the nature of its operation at the moment.

The scattered herd

We carry out measurements together with our good friends from the AGP Motorsport workshop - on a modern Dynomax 5000 AWD dynamometer with running drums, which is designed for any type of drive. Before driving the cars onto the drums, a few words about the test methodology.

Now all manufacturers measure power at the engine flywheel with all auxiliary equipment. Naturally, we cannot remove the engine from every car. It is clear that the bench power “from the wheels” when accelerating in direct gear from 1500–2000 rpm to maximum speed will be significantly less than the net power at the flywheel. Because transmission losses are inevitable. That is why any modern stand can recalculate the results taking into account all losses.

Another coefficient automatically applied by the stand concerns test conditions. According to UNECE rules No. 85 and ISO 1585, the ambient temperature should be +25 °C, atmospheric pressure - 99 kPa.

However, the stand still gives an error that does not exceed 5%. As our experience shows, this error is always not in favor of the motorist. But if the obtained data fits into these percentages, we consider that the engine power and torque are indicated honestly.

To confirm the results of the stand, we will also measure the dynamics, that is, the acceleration time from standstill to 100 km/h.

NET AND GROSS

How is engine power measured when compiling technical data for a new car? Once upon a time, manufacturers operated with gross power, or so-called laboratory power, which was removed from the engine without attachments. It is clear that in this case the indicators are higher, but these data have nothing to do with the real return on wheels. Therefore, such measurements were gradually abandoned in favor of net power measured at the engine flywheel with all auxiliary equipment.

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.

Checking at a car service center

A surefire way to learn everything about a car and its engine if you don't consider yourself a good expert to inspect it yourself. For a reasonable fee, service specialists will inspect the car completely, consider it a computer (if the car has a diagnostic connector), check all the technical components of the car and even find out whether there has been interference in the memory of the on-board computer, whether the mileage has been changed through it and whether errors have been erased.

It is better to contact either official dealers or specialized centers that work with one brand of car, or with a narrow range of car brands. As a rule, such services know better all the typical “sores” of cars and are very well versed in the engines presented on the brand’s models.

In this case, you only need to choose a service that has a large number of positive reviews and a long history of work, pay for the service and wait until the diagnostics are completed, after which you will be given a work order. Whether you buy a car after that and pay for spare parts and repairs, or hand over the document to the seller and refuse to buy the car, is up to you. This method of checking a car engine is very effective and, as a rule, error-free - if the car is faulty or requires significant investment, specialists will report this based on the diagnostic results.

Advantages of using a car service:

You will know for sure all the ins and outs of the car and its components: they will tell you whether the car’s mileage was low, whether there were any accidents, what exactly needs to be replaced or repaired at a given time, etc.
They will issue an order on the spot and tell you where to purchase spare parts and consumables. If you purchase a car right on the spot, you can begin to work on fixing problems without going anywhere.

Disadvantages of working with a car dealership:

It is necessary to pay for the services of a specialized service; prices vary depending on the region and the qualifications of the servicemen. On average, for services specializing in foreign cars, one standard hour is estimated at 900 to 2000 rubles, diagnostics last an hour and a half, these costs are borne by the potential buyer.
You will have to spend time on the road to the service, diagnosing the car and then on the way home, you also need to agree on a time that is convenient for all parties: you, the seller and the car service center. Due to the complexity of the organization, the process can take weeks.
If you choose an inexpensive service “behind garages,” there is a risk that the diagnostics will not be carried out efficiently, which will result in additional expenses for you after purchasing the car.

If you have enough time and are willing to spend several thousand rubles to definitely avoid mistakes, then the service is your option. But be careful when choosing the service itself; saving here is not the best way; it is better to spend more money on the services of high-level specialists.

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.

Mechanical loss error

As mentioned above, when determining a number of parameters, mechanical losses are not taken into account, which do not allow obtaining an accurate result of engine power. Such losses are:

Friction. The main losses that occur are crankshafts, pistons, cylinders, bearings, bushings. The indicator increases with increasing load, deterioration of engine condition, rotation speed, surface treatment, disruption of lubrication and cooling systems, and the use of low-quality oil.
Pumping. Losses for pumping strokes of the piston. Determined by the resistance value of the exhaust/intake pipelines. The indicator changes depending on the degree of opening of the throttle valve and an increase in the crankshaft speed.
Auxiliary. These are various manisms (pumps, fan, generator, and so on). the level of losses depends on the design of the units, their condition and size.
Supercharger. Refers to the mechanical drive of the compressor in a supercharged internal combustion engine (turbocharged engines do not apply). Such a compressor is rarely used and has minor losses.
Hydraulic. Overcoming the resistance to movement of parts is taken into account.

Internal losses of indicator power are the sum of all the above types of indicators.

It is not necessary to know all the specified data for the calculation.
You can find out the power of the power unit in separate ways. The value is that it is designed for those models that have undergone tuning of the body and power unit. To obtain the most accurate results, it is better to contact qualified specialists. They will help not only determine engine power, but also identify faults in the power unit, make the necessary adjustments and give valuable advice. Looks like you have blocked notifications!

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:

M = (PF x CF x SC)/(CT x TD)

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:

M = M(LS) x 0.735

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”.