Fuel Injector Size Calculator

Fuel Injector Size Formula:

\[ Size = \frac{HP \times BSFC}{Number \times Duty Cycle} \]

HP (hp):

BSFC (lb/hp-hr):

lb/hp-hr

Number (injectors):

injectors

Duty Cycle (decimal):

decimal

Size (lb/hr):

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1. What is the Fuel Injector Size Calculation?

The fuel injector size calculation determines the required flow rate for fuel injectors based on engine horsepower, brake specific fuel consumption, number of injectors, and duty cycle. Proper injector sizing is crucial for optimal engine performance and fuel delivery.

2. How Does the Calculator Work?

The calculator uses the fuel injector size formula:

\[ Size = \frac{HP \times BSFC}{Number \times Duty Cycle} \]

Where:

\( Size \) — Injector size (lb/hr)
\( HP \) — Horsepower (hp)
\( BSFC \) — Brake specific fuel consumption (lb/hp-hr)
\( Number \) — Number of injectors
\( Duty Cycle \) — Injector duty cycle (decimal)

Explanation: The equation calculates the required fuel flow rate per injector to support the engine's power output while maintaining proper fuel delivery efficiency.

3. Importance of Proper Injector Sizing

Details: Correct injector sizing ensures optimal fuel delivery, prevents lean or rich conditions, maintains engine reliability, and supports maximum performance potential. Undersized injectors can cause fuel starvation, while oversized injectors can lead to poor idle quality and drivability issues.

4. Using the Calculator

Tips: Enter horsepower in hp, BSFC in lb/hp-hr (typically 0.45-0.65 for naturally aspirated engines, 0.55-0.75 for forced induction), number of injectors, and duty cycle as a decimal (typically 0.80-0.85 for safe operation). All values must be valid positive numbers.

5. Frequently Asked Questions (FAQ)

Q1: What is BSFC and how do I determine it?
A: Brake Specific Fuel Consumption measures fuel efficiency. Typical values range from 0.45-0.65 lb/hp-hr for NA engines and 0.55-0.75 for forced induction. Conservative estimates are recommended for safety.

Q2: What duty cycle should I use?
A: For street applications, 80-85% duty cycle is recommended for safety margin. Racing applications may use up to 90-95% but with increased risk.

Q3: How does injector number affect the calculation?
A: More injectors distribute the fuel load, allowing smaller individual injectors. The calculation divides total fuel requirement by the number of injectors.

Q4: Should I account for future power upgrades?
A: Yes, it's recommended to size injectors for your target horsepower rather than current power to avoid needing upgrades later.

Q5: How do I convert lb/hr to cc/min?
A: Multiply lb/hr by 10.5 to get approximate cc/min (1 lb/hr ≈ 10.5 cc/min).