This calculator helps you determine the required flow rate for your fuel injectors based on your engine's horsepower. Proper injector sizing is crucial for optimal engine performance, fuel efficiency, and preventing lean or rich conditions. Too small injectors may not supply enough fuel, leading to detonation and engine damage, while injectors that are too large can lead to poor atomization at low pulse widths, causing rough idling and inefficient combustion.
The calculation is based on a commonly used formula that factors in your engine's maximum expected horsepower and a safety margin (duty cycle). A typical duty cycle for gasoline engines is around 80% to account for injector opening and closing times, as well as ensuring the injector isn't operating at its absolute maximum capacity continuously.
Required Injector Flow Rate:
function calculateInjectorFlowRate() {
var maxHorsepower = parseFloat(document.getElementById("maxHorsepower").value);
var injectorDutyCycle = parseFloat(document.getElementById("injectorDutyCycle").value);
var fuelPressure = parseFloat(document.getElementById("fuelPressure").value);
var fuelSpecificGravity = parseFloat(document.getElementById("fuelSpecificGravity").value);
var resultDiv = document.getElementById("result");
var injectorFlowRateLPH = document.getElementById("injectorFlowRateLPH");
var injectorFlowRateCC = document.getElementById("injectorFlowRateCC");
var injectorFlowRateLBS = document.getElementById("injectorFlowRateLBS");
if (isNaN(maxHorsepower) || isNaN(injectorDutyCycle) || isNaN(fuelPressure) || isNaN(fuelSpecificGravity) ||
maxHorsepower <= 0 || injectorDutyCycle 100 || fuelPressure <= 0 || fuelSpecificGravity <= 0) {
resultDiv.innerHTML = "
Error: Please enter valid positive numbers for all fields.
";
return;
}
// Calculate required fuel flow in pounds per hour (PPH)
// This formula assumes 1 HP requires approximately 0.5 lbs of fuel per hour for naturally aspirated gasoline engines.
// For forced induction, this multiplier might need adjustment or a more complex formula.
var fuelConsumptionPerHP = 0.5; // lbs/hp/hr
var totalFuelFlowPPH = maxHorsepower * fuelConsumptionPerHP / (injectorDutyCycle / 100);
// Convert PPH to Liters Per Hour (LPH)
// 1 lb of gasoline is approximately 0.453592 kg. Density of gasoline is ~740 kg/m^3 (using specific gravity).
// So, 1 lb of gasoline is ~0.453592 kg / 740 kg/m^3 = ~0.000613 m^3 = 0.613 Liters.
// A more precise conversion factor for gasoline from PPH to LPH at 43.5 PSI (which implies around 3 bar gauge) is approximately 10.5
// However, a direct conversion using density and pressure is more robust if specific gravity is known.
// Let's use a known conversion factor for gasoline at ~43.5 PSI, which is roughly 1 PPH = 0.0105 LPH.
// For a more accurate calculation based on fuel pressure and specific gravity, we'd need more complex fluid dynamics.
// The common "rule of thumb" LPH calculation from HP is often simplified.
// A direct common method for LPH from HP is often cited as:
// LPH = (HP * BSFC * 1.25) / injector_duty_cycle
// Where BSFC (Brake Specific Fuel Consumption) for gasoline is around 0.4 to 0.6. Let's use 0.5 for a general estimate.
// However, the PPH calculation is a more fundamental starting point.
// Let's stick to converting PPH to LPH using a density-based approach and then demonstrate CC.
// 1 US Gallon of gasoline is approx 6.3 lbs. 1 US Gallon = 3.78541 Liters.
// So, 1 lb gasoline = 3.78541 / 6.3 Liters ≈ 0.6008 L.
var lbsToLitersConversion = 0.6008; // L per lb of gasoline
var totalFuelFlowLPH = totalFuelFlowPPH * lbsToLitersConversion;
// Convert LPH to Cubic Centimeters per minute (CC/min)
// 1 Liter = 1000 CC. 1 Hour = 60 Minutes.
var lphToCcmConversion = 1000 / 60; // CC/min per LPH
var totalFuelFlowCCM = totalFuelFlowLPH * lphToCcmConversion;
injectorFlowRateLPH.innerHTML = "Flow Rate: " + totalFuelFlowLPH.toFixed(2) + " LPH (Liters Per Hour)";
injectorFlowRateCC.innerHTML = "Flow Rate: " + totalFuelFlowCCM.toFixed(2) + " CC/min (Cubic Centimeters Per Minute)";
injectorFlowRateLBS.innerHTML = "Flow Rate: " + totalFuelFlowPPH.toFixed(2) + " PPH (Pounds Per Hour)";
}