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BMEP Calculator (Brake Mean Effective Pressure Calculator)

Created by Madhumathi Raman
Reviewed by Hanna Pamuła, PhD and Jack Bowater
Last updated: Jan 18, 2024


The BMEP calculator helps in finding the BMEP (Brake Mean Effective Pressure) of an engine, which is a useful metric to compare the performance of different engines of similar types. Here, we will see what BMEP is, how to calculate the BMEP of an engine and also learn more about the BMEP formula that's used to calculate this value.

Knowing what BMEP is, is pretty important, since the Brake Mean Effective Pressure value gives you a sense of how efficient your engine is.

What is BMEP?

BMEP stands for Brake Mean Effective Pressure. Our BMEP calculator measures the average pressure applied across the pistons to produce torque at the crankshaft. We can use this performance metric to compare different engines.

It's also interesting to note that the engine efficiency also depends on the amount of air-fuel that is handled by the carburetor, and the carburetor CFM metric provides a measure of that volume.

BMEP formula

The formula used to calculate BMEP is as follows:

BMEP=2πnTD\mathrm{BMEP} = \frac{2π n T} {D}

where,

  • n - Number of revolutions per power stroke;
  • T - Torque; and
  • D - Displacement (volume) of the engine.

It is to be noted that the value of n is standard -

  • n = 1 for a two-stroke engine; and
  • n = 2 for a four-stroke engine.

If you're curious, you may even try converting torque to horsepower, or use a power converter to convert the horsepower value into various other units.

How do we calculate the BMEP of an engine?

Let's say we have a 4-stroke engine with a volume (displacement) of 2000 cc and an indicated torque of 160 Nm. This is how we calculate the BMEP of the engine -

  1. In the BMEP calculator, set the type of the engine to 4-stroke. Once this is selected, n is automatically set to 2.
  2. Set the torque value as 160 Nm160 \ \mathrm{Nm}.
  3. Set the displacement value as 2000 cc2000 \ \mathrm{cc}.
  4. Voila! The BMEP calculator gives a result of 1,005.3 kPa1,005.3 \ \mathrm{kPa}.

Conversely, if we know the BMEP value, we can convert BMEP to torque by using the same formula and rearranging it to solve for torque. Converting BMEP to torque is especially useful since torque is an important metric that represents the load that the engine can handle.

Additionally, if you're curious about how horsepower can help in comparing engine efficiencies, you may try calculating the horsepower of different engines! You may also be interested in knowing about the various factors that affect the piston speed and the piston force using our piston speed calculator and piston force calculator.

FAQ

Why is the BMEP important?

BMEP is responsible for the torque produced by the engine. If we can increase the BMEP of a given engine, we can observe a proportional increase in its output torque!

What is the difference between two-stroke and four-stroke engines?

During one power stroke, the two-stroke engine has one revolution of the crankshaft and generates more torque, while a four-stroke engine has two revolutions of the crankshaft and generates less torque. A four-stroke engine tends to emit less smoke and is more efficient compared to a two-stroke engine.

How can BMEP be increased?

Some things you can try to increase the BMEP of an engine:

  1. Increasing the compression ratio.
  2. Increasing the quantity of air-fuel mixture in the chamber by supercharging or turbocharging.
  3. Shorter stroke length.
  4. Enriching the air-fuel mixture.

Does the BMEP of a diesel engine vary from that of a petrol engine?

Generally, diesel engines have higher compression ratios than their petrol counterparts and hence have higher BMEP. However, note that BMEP comparison is usually reserved for similar engines. For example, we can compare the BMEP of different diesel engines, but not with petrol engines.

Madhumathi Raman
Engine type
Four Stroke Engine
Engine displacement (Volume)
cu in
Torque
lbf·ft
Brake mean effective pressure
psi
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