BMEP lets you compare how hard engines of different sizes work. Naturally aspirated petrol engines reach about 10–13 bar; turbocharged ones 20–30 bar; truck diesels around 20+ bar.
How to use the Brake Mean Effective Pressure
- Engine type
- Engine displacement
- Torque
Results update as you type, every field has its own unit menu, and everything is calculated in your browser.
How it works
Choose the engine cycle, enter the displacement and torque (at the same rpm).
Inputs explained
| Field | What to enter |
|---|---|
| Engine type | Choose one: Four-stroke, Two-stroke |
| Engine displacement | Units: cm³ (cc), L, in³ (CID), m³ |
| Torque | Units: N·m, lbf·ft, kgf·m, N·mm |
What each result means
- Brake mean effective pressure = 2×pi×[Engine type]×[Torque]÷[Engine displacement]
- Specific torque = [Torque]÷([Engine displacement]×1000)
Example values
How the main result changes when Engine displacement changes and everything else stays at the example values above:
| Engine displacement (cm³ (cc)) | Brake mean effective pressure (bar) |
|---|---|
| 1,000 | 25.1327 |
| 1,500 | 16.7552 |
| 2,000 | 12.5664 |
| 2,500 | 10.0531 |
| 3,000 | 8.3776 |
| 4,000 | 6.2832 |
Formula
BMEP = 2π·n_c·T / V_d (n_c = 2 for four-stroke, 1 for two-stroke)
Worked example
Inputs — Engine type: Four-stroke; Engine displacement: 2,000 cm³ (cc); Torque: 200 N·m.
Results — Brake mean effective pressure = 12.5664 bar; Specific torque = 100 N·m/L.
Key terms
- Displacement
- Total swept volume of all cylinders.
Frequently asked questions
What is a good BMEP?
10–13 bar for naturally aspirated petrol engines; 20+ bar turbocharged.
Why use BMEP?
It removes engine size, so efficiency of different engines can be compared.
Is BMEP a real pressure?
No – it is a theoretical average over the cycle.
How does turbocharging raise BMEP?
More air per cycle allows more fuel and torque.