Our injector calculator enables you to find the right size injector for your application work.
All engines require the proper amount of fuel at the right timing, and this is where injectors are important.
By knowing the horsepower of your engine, fuel flow rate (BSFC), and amount of injectors it is very easy to calculate simplified differential pressure in the injector.
And would you like to learn the math behind injector sizing, its terms and how it relates to NA alive? Look no further—you’ve landed on the right tool!
Fuel Injector Calculator
Injector Flow Rate (lb/hr) =
(Engine HP × Brake Specific Fuel Consumption) ÷ Number of Injectors
BSFC is typically:
• ~0.45–0.55 for naturally aspirated engines
• ~0.60–0.75 for turbo/supercharged engines
Understanding the Formula
The Fuel Injector Flow Rate tells us how much fuel each injector must supply to support the engine's horsepower. The formula is:
- Engine HP: Power output of the engine (how much work it can do).
- BSFC (lb/hp/hr): Fuel required to produce 1 horsepower for 1 hour.
- Number of Injectors: Total injectors dividing the fuel load equally.
Worked-Out Example
Suppose you have a 400 HP naturally aspirated engine. The typical Brake Specific Fuel Consumption (BSFC) for such engines is about 0.50 lb/hp/hr. The engine uses 8 fuel injectors. Let’s calculate the required injector flow rate.
• Engine HP = 400
• BSFC = 0.50 lb/hp/hr
• Number of Injectors = 8
Step 2: Recall the formula
Injector Flow Rate = (Engine HP × BSFC) ÷ Number of Injectors
Step 3: Substitute values
= (400 × 0.50) ÷ 8
Step 4: Calculate
= 200 ÷ 8 = 25 lb/hr
✅ Final Answer: Each injector must flow 25 lb/hr.
Fuel Injector Reference Table
This table shows sample calculations of required injector flow rates for different engine setups.
| Engine HP | BSFC (lb/hp/hr) | Injectors | Flow Rate per Injector (lb/hr) |
|---|---|---|---|
| 150 | 0.45 | 4 | 16.9 |
| 200 | 0.50 | 4 | 25.0 |
| 250 | 0.55 | 6 | 22.9 |
| 300 | 0.60 | 6 | 30.0 |
| 350 | 0.55 | 8 | 24.1 |
| 400 | 0.50 | 8 | 25.0 |
| 450 | 0.65 | 6 | 48.8 |
| 500 | 0.70 | 8 | 43.8 |
| 600 | 0.65 | 8 | 48.8 |
| 700 | 0.75 | 8 | 65.6 |
FAQs
Q1: What is a fuel injector flow rate?
A fuel injector flow rate tells you how much fuel each injector needs to deliver per hour to meet your engine’s power demand.
Q2: How do I use the formula for injector sizing?
Simply multiply your engine’s horsepower by the BSFC, then divide by the number of injectors. That gives you the flow rate per injector.
Q3: What is BSFC and why does it matter?
BSFC stands for Brake Specific Fuel Consumption. It tells you how much fuel the engine uses to produce 1 horsepower for 1 hour. It’s key for choosing the right injector.
Q4: Can this calculator be used for turbocharged engines?
Yes! Just use the BSFC value for turbo or supercharged engines (usually higher than naturally aspirated) and the calculator will give the correct injector flow.