The Brake Mean Effective Pressure Calculator is here to help you calculate BMEP for your engine.
Read on to learn what BMEP is and why it’s important in engine performance.
We’ll also explain how to find BMEP in exercises using the BMEP formula. At the end, we also illustrate how BMEP relates to engine efficiency with an easy example.
If you want to calculate BMEP for a specific engine, this calculator can make it quick and easy:
Brake Mean Effective Pressure (BMEP) Calculator
BMEP, or Brake Mean Effective Pressure, is the average pressure in the engine cylinders that actually pushes the pistons to produce power.
And, as you see from the BMEP formula, the greater the power, the higher the BMEP.
So, if an engine produces more power at a certain speed, it can generate a stronger push inside the cylinders. This pressure is proportional to the engine’s power and inversely proportional to its displacement and RPM.
Another way to look at it is through the terms in the formula:
- Power is like the strength of the engine; the more power it has, the more pressure it can create.
- Displacement is the total volume of all the cylinders. A bigger engine spreads the pressure over a larger volume, so for the same power, BMEP is lower.
- RPM is how fast the engine is running.
- Factor adjusts for engine type: 120 for 4-stroke engines and 60 for 2-stroke engines, because 4-stroke engines produce power every two revolutions while 2-stroke engines produce power every revolution.
Example BMEP Calculation
• Power = 240 kW
• Displacement = 8.5 liters
• RPM = 1800
• Factor = 120 (4-stroke engine)
BMEP = (Factor × Power) / (Displacement × RPM)
BMEP = (120 × 240) / (8.5 × 1800)
BMEP = 28,800 / 15,300
BMEP = 1.88 bar
The BMEP of 1.88 bar (approximately 27.3 psi) indicates good efficiency for a diesel engine.
BMEP Reference Table
| Engine Type | BMEP (bar) | Efficiency/Notes |
|---|---|---|
| Small Diesel Engine | 1.5 – 2.0 | Good efficiency |
| Medium Diesel Engine | 1.8 – 3.0 | Typical BMEP |
| Large Diesel Engine | 2.5 – 3.5 | High efficiency |
| Turbocharged Diesel | 3.0 – 4.5 | Very high efficiency |
| Gasoline Engine | 0.8 – 1.2 | Normal range |
| High Performance Gasoline | 1.2 – 1.8 | Sport / racing engines |
FAQs
What is BMEP?
BMEP stands for Brake Mean Effective Pressure. It is the average pressure in the engine cylinders that produces torque. BMEP lets you compare engines of different sizes. For example, a small engine and a large engine might make the same power.
Is BMEP the same as engine power?
No. Engine power measures how fast the engine does work. BMEP measures the pressure that produces torque. For example, two engines might both produce 240 kW.
Does BMEP show engine efficiency?
Yes. Higher BMEP usually means the engine converts fuel into torque more efficiently. For example, a diesel engine with BMEP of 1.88 bar is doing well for its size.
Can BMEP be negative?
No. BMEP measures the effective pressure producing torque. It is always positive in normal operation. Even when the engine is braking or slowing down, the calculation is based on effective work, so BMEP stays positive.