Fuel Injector Size Calculator

Find the injector size for your target power — or the max power your injectors support.


Reverse: max HP from injector size

How it works

1

Enter target power

Use crank/flywheel HP. BSFC defaults: 0.50 N/A petrol, 0.60 boosted, 0.65 for E85.

2

Set injectors & duty

Number of injectors and a safe max duty cycle (80–85% is typical).

3

Get the size

We give the required cc/min and lb/hr per injector — round up to the next available size.

Frequently asked questions

How are injector sizes calculated?

Total fuel flow (lb/hr) = HP × BSFC. Per injector cc/min = (HP × BSFC × 10.5) ÷ (injectors × duty cycle). We use BSFC 0.50–0.65 depending on fuel and boost.

What duty cycle should I use?

Keep maximum injector duty around 80–85% at peak power. Running closer to 100% leaves no headroom and risks a lean condition.

Do E85 injectors need to be bigger?

Yes — E85 needs roughly 30–40% more fuel volume than petrol, so injectors must be sized up accordingly. Select the E85 option for the right BSFC.

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