Our fuel injector calculator helps you estimate the right injector size for your engine.
Fuel injectors are key to delivering the right amount of fuel into the engine cylinders for efficient combustion. If the injectors are too small, your engine may starve for fuel. If they’re too big, you risk wasting fuel and losing performance.
Do you want to know how to calculate fuel injector size, the role of brake-specific fuel consumption (BSFC), and how horsepower links to injector flow rate?
Are you curious about how injector duty cycle affects performance? Look no further because you’ve come to the right place!
🔬 Viscosity Index Calculator
📘 Viscosity Index Formulas Explained
Method 1: Traditional Formula (VI ≤ 100)
VI = [(L – U) / (L – H)] × 100
- U → Measured kinematic viscosity of the oil at 40°C
- L → Reference viscosity at 40°C (VI = 0)
- H → Reference viscosity at 40°C (VI = 100)
Method 2: Extended Formula (VI > 100)
N = (log(H) – log(U)) / log(v₁₀₀)
VI = [(10^N – 1) / 0.00715] + 100
- U → Measured viscosity at 40°C
- H → Reference viscosity at 40°C (VI = 100)
- v₁₀₀ → Measured viscosity at 100°C
- N → Derived constant for VI > 100
📝 Worked Example of Viscosity Index
Step 1: Given Data
- U = 50.0 cSt (Viscosity at 40°C)
- L = 100.0 cSt (Reference oil at 40°C, VI = 0)
- H = 70.0 cSt (Reference oil at 40°C, VI = 100)
Step 2: Formula
VI = [(L – U) / (L – H)] × 100
Step 3: Substitution
VI = [(100 – 50) / (100 – 70)] × 100
Step 4: Simplification
VI = (50 / 30) × 100 = 166.67
✅ Final Answer
The viscosity index of this oil is 166.7, which indicates that the extended method (Method 2) is needed for accuracy.
📊 ASTM Reference Values (L and H)
| Viscosity at 100°C (cSt) | L (VI = 0) at 40°C (cSt) | H (VI = 100) at 40°C (cSt) |
|---|---|---|
| 2.0 | 6.6 | 3.8 |
| 3.0 | 10.5 | 6.3 |
| 4.0 | 14.6 | 8.7 |
| 5.0 | 19.0 | 11.0 |
| 6.0 | 23.5 | 13.3 |
| 8.0 | 32.7 | 18.0 |
| 10.0 | 42.0 | 22.5 |
| 12.0 | 51.5 | 27.0 |
| 14.0 | 61.0 | 31.5 |
| 16.0 | 70.0 | 36.0 |
*Adapted from ASTM D2270 tables (sample values for understanding).
FAQs
What is a fuel injector?
A fuel injector is a tool that injects fuel into the engine’s intake air stream, or directly into the cylinder. It keeps the correct mix of air and fuel in place to optimize engine performance.
Why do I need to calculate injector size?
Because wearing the wrong size isn’t just uncomfortable — it can also mess up your performance! Too large, and there won’t be enough fuel for your engine. A hair too rich and it will flood and waste fuel.
What is injector duty cycle?
Injector duty cycle informs us the amount of time the injector is open relative to that period of time.engine cycle. Running injectors at 100% all the time is risky. Ideally, we keep them around 80–85% for safe and reliable performance.
How does horsepower affect injector size?
Horsepower is directly linked to how much fuel your engine needs. More horsepower = more fuel = larger injectors. That’s why horsepower is a key input when calculating injector size.