Deatschwerks Fuel Injector Calculator

Injector Size Formula:

\[ Injector_{lb/hr} = \frac{HP \times BSFC}{n_{injectors} \times duty\_cycle} \]

Horsepower (HP):

Brake Specific Fuel Consumption (BSFC):

lb/HP-hr

Number of Injectors:

count

Duty Cycle:

fraction (0-1)

Required Injector Size:

Unit Converter ▲

Unit Converter ▼

From:	To:

1. What is the Injector Size Calculation?

The injector size calculation determines the required fuel flow rate for your engine based on horsepower, fuel consumption, number of injectors, and their duty cycle. Proper sizing ensures your engine gets adequate fuel without overworking the injectors.

2. How Does the Calculator Work?

The calculator uses the standard injector sizing formula:

\[ Injector_{lb/hr} = \frac{HP \times BSFC}{n_{injectors} \times duty\_cycle} \]

Where:

\( HP \) — Engine horsepower
\( BSFC \) — Brake specific fuel consumption (typically 0.45-0.60 for NA engines, 0.60-0.75 for forced induction)
\( n_{injectors} \) — Number of fuel injectors
\( duty\_cycle \) — Maximum injector duty cycle (typically 0.80-0.85 for safety margin)

Explanation: The equation calculates the required fuel flow per injector based on total engine fuel demand divided by the number of injectors and their operating percentage.

3. Importance of Proper Injector Sizing

Details: Correct injector sizing prevents lean conditions (too small) or poor idle quality (too large). It's critical for engine performance, reliability, and emissions.

4. Using the Calculator

Tips: Enter realistic HP numbers (dyno verified if possible). Use conservative BSFC values (higher for safety). Keep duty cycle ≤85% for reliability. All values must be positive numbers.

5. Frequently Asked Questions (FAQ)

Q1: What's a typical BSFC value?
A: Naturally aspirated gasoline engines: 0.45-0.50. Turbocharged/supercharged: 0.55-0.65. High boost applications may require 0.65-0.75.

Q2: Why limit duty cycle to 80-85%?
A: Provides safety margin for temperature variations, fuel pressure changes, and prevents injector lock-up at 100% duty.

Q3: Should I round up my injector size?
A: Yes, round up to the nearest available injector size. It's better to have slightly more capacity than needed.

Q4: How does fuel pressure affect this calculation?
A: This calculation assumes standard fuel pressure. If changing pressure, injector flow changes by square root of pressure ratio.

Q5: What about E85 or other fuels?
A: For E85 (30% more fuel required), multiply result by 1.3. For methanol, multiply by approximately 2.0.