Indicated Power Calculator

What Is Indicated Power?

Indicated power (IP) is the total power generated inside the engine cylinders. It is calculated from combustion pressure acting on the piston.

It does not include:

• Friction losses
• Pumping losses
• Accessory drag
• Drivetrain losses

In simple words:

Indicated power is the raw power created by combustion before anything steals energy from it.

Engineers use this value to understand combustion efficiency and engine performance potential.

What Is IMEP?

The calculator uses Indicated Mean Effective Pressure (IMEP) as a core input.

IMEP is the average pressure inside the cylinder during the power stroke. It is not peak pressure. Instead, it represents usable average combustion pressure.

Higher IMEP usually means:

• Better cylinder filling
• Stronger combustion
• Higher torque
• More power

Typical IMEP ranges:

Indicated Power Formula

The calculator uses this formula:

[
Indicated\ Power\ (HP) = \frac{IMEP × Displacement × RPM × Cylinders}{792000 × Power\ Factor}
]

Where:

• IMEP is in psi
• Displacement is in cubic inches
• RPM is engine speed
• Power factor = 1 for 2-stroke, 2 for 4-stroke

The constant 792000 converts units into horsepower.

For kilowatts:

[
kW = HP × 0.7457
]

How the Indicated Power Calculator Works

The calculator asks for six main inputs:

1. Indicated Mean Effective Pressure (IMEP)

You can enter IMEP in:

• psi
• bar
• kPa

The calculator automatically converts the value to psi internally.

Example:

• 10 bar = 145 psi
• 1000 kPa ≈ 145 psi

2. Engine Displacement

You can enter displacement in:

• Cubic inches (CID)
• Cubic centimeters (cc)
• Liters

The calculator converts everything to cubic inches.

Examples:

• 350 CID
• 5.7 liters
• 5700 cc

All represent roughly the same engine size.

3. Engine Speed (RPM)

Enter engine speed in revolutions per minute.

Typical values:

• Idle: 700–900 RPM
• Street engines: 2000–6500 RPM
• Race engines: 7000–10000+ RPM

Higher RPM increases power, but only if IMEP remains strong.

4. Engine Cycle

You choose:

• 2-Stroke
• 4-Stroke

Important difference:

• 2-stroke fires every revolution
• 4-stroke fires every two revolutions

This directly affects the power calculation.

5. Number of Cylinders

Enter total cylinders in the engine.

Examples:

• 4 cylinders
• 6 cylinders
• 8 cylinders

More cylinders generally increase total power if IMEP stays the same.

6. Mechanical Efficiency (Optional)

Mechanical efficiency accounts for friction and pumping losses.

Typical values:

• 80–90% for most engines
• 85% is a common average

If left blank, the calculator assumes 85%.

This allows the tool to estimate:

• Brake horsepower (power at crankshaft)
• Friction losses

What the Calculator Outputs

After clicking Calculate Power, the tool provides:

1. Indicated Power (Gross)

Displayed in:

• Horsepower (HP)
• Kilowatts (kW)

This is the raw combustion power.

2. Engine Classification

Based on IMEP, the calculator categorizes your engine as:

• Low Performance
• Production Street
• Performance Street
• Racing / High Boost
• Extreme Performance

This helps you quickly understand where your engine stands.

3. Torque

Torque is calculated using:

[
Torque (lb-ft) = \frac{HP × 5252}{RPM}
]

Also converted into Newton-meters.

Torque tells you how strong the engine feels under load.

4. Piston Speed

The tool estimates average piston speed in feet per minute (FPM).

High piston speed means:

• More stress
• Increased wear
• Reduced durability

Race engines operate at much higher piston speeds than street engines.

5. Brake Power Estimate

If mechanical efficiency is entered, the calculator estimates:

• Brake horsepower
• Friction horsepower

Example:

If indicated power = 500 HP
Mechanical efficiency = 85%

Brake power = 425 HP
Friction losses = 75 HP

This gives a realistic performance expectation.

Indicated Power vs Brake Power vs Wheel Power

It is important to understand the difference:

Wheel power is usually 10–15% lower than brake power.

So if your calculator shows 400 HP brake power, you might see 340–360 HP at the wheels.

Example Calculation

Let’s use real numbers:

• IMEP: 150 psi
• Displacement: 350 CID
• RPM: 6000
• 4-stroke
• 8 cylinders
• 85% efficiency

The calculator would estimate roughly:

• Indicated Power ≈ 530 HP
• Brake Power ≈ 450 HP
• Friction Loss ≈ 80 HP

This is typical of a strong naturally aspirated V8 street engine.

Why Indicated Power Matters

Understanding indicated power helps you:

• Compare engine designs
• Evaluate combustion efficiency
• Analyze forced induction gains
• Tune engines more precisely
• Predict performance before dyno testing

It separates combustion performance from mechanical losses.

For engine builders and tuners, this is valuable data.

Who Should Use an Indicated Power Calculator?

This tool is useful for:

• Engine builders
• Performance tuners
• Automotive engineering students
• Racing teams
• Anyone designing custom engines

It gives a fast theoretical estimate before real-world testing.

Limitations of the Calculator

While helpful, it is still an estimation tool.

It assumes:

• Uniform pressure distribution
• Stable combustion
• No abnormal losses
• Ideal volumetric efficiency

Real engines vary due to:

• Heat
• Fuel quality
• Valve timing
• Boost variations
• Air density

Always confirm final results with dyno testing.