Calculate Nitrous and Fuel Jet Orifice Sizes for Target Horsepower
Single Nozzle / Plate
Direct Port (Per Cylinder)
Recommended Orifice Sizes
Nitrous Jet.000
Fuel Jet.000
*Always start with a richer fuel jet and smaller nitrous jet to safely tune your engine.
Understanding Nitrous Jetting
In a nitrous oxide system, the "jet" is a precision-drilled orifice that restricts the flow of nitrous and fuel. Achieving the correct horsepower increase requires balancing the flow of both components to maintain a safe Air/Fuel Ratio (AFR). Improper jetting can lead to "lean" conditions, causing catastrophic engine failure.
The Physics of Jet Flow
Nitrous jetting isn't linear. Flow is determined by the area of the hole and the pressure differential. A .040 jet does not flow double what a .020 jet flows; it flows significantly more because the area increases with the square of the radius.
Jetting Formula and Factors
Nitrous Pressure: Most systems are designed for 900–1000 PSI. If your bottle pressure drops, the system runs rich; if it's too high, it runs lean.
Fuel Pressure: Carbureted systems usually run low pressure (5–7 PSI), requiring very large fuel jets. EFI systems run high pressure (40–60 PSI), requiring much smaller fuel jets.
The Ratio: We calculate the flow area required for the target HP and then determine the fuel jet size based on the specific gravity of the fuel and the pressure available.
Example Tuning Chart (Single Nozzle)
HP Gain
Nitrous Jet
Fuel (EFI 45 PSI)
Fuel (Carb 6 PSI)
50 HP
.035
.020
.032
100 HP
.052
.033
.047
150 HP
.063
.038
.055
Safety Guidelines
1. Start Small: Never jump to a 200HP shot without testing 50HP and 100HP first.
2. Read Spark Plugs: Plugs are the best indicator of combustion heat and mixture.
3. Fuel Pump: Ensure your fuel pump can handle the extra volume required by the nitrous system.
function calculateNitrousJets() {
var targetHP = parseFloat(document.getElementById("targetHP").value);
var n2oPressure = parseFloat(document.getElementById("n2oPressure").value);
var fuelPressure = parseFloat(document.getElementById("fuelPressure").value);
var systemType = document.getElementById("systemType").value;
if (isNaN(targetHP) || isNaN(n2oPressure) || isNaN(fuelPressure)) {
alert("Please enter valid numeric values.");
return;
}
// Horsepower per jet calculation
// If direct port, HP is divided by 8 (assuming 8 cylinder) for the jet size per nozzle
var hpPerNozzle = targetHP;
if (systemType === "direct") {
hpPerNozzle = targetHP / 8;
}
// Base Nitrous Calculation (Simplified Orifice Flow)
// Formula derived from standard Holley/NOS flow tables
// Area proportional to HP. Jet Diameter = sqrt(HP / Constant)
// Constant for N2O at 950 PSI is approx 0.04
var baseN2OJet = Math.sqrt(hpPerNozzle / 0.038);
// Pressure Correction for Nitrous (Flow proportional to sqrt(pressure))
var n2oCorrection = Math.sqrt(950 / n2oPressure);
var finalN2OJet = baseN2OJet * n2oCorrection;
// Fuel Jet Calculation
// We need to maintain a roughly 5:1 to 8:1 N2O to Fuel mass ratio
// High pressure EFI requires smaller jets, Low pressure Carb requires larger jets
// Fuel flow = Area * sqrt(Pressure)
// Area_fuel = (Area_n2o * sqrt(P_n2o)) / (Ratio * sqrt(P_fuel))
// Constants used here represent typical mass flow requirements
var ratioConstant = 7.5; // Tuning ratio factor
var n2oArea = Math.pow(finalN2OJet, 2);
var fuelArea = (n2oArea * Math.sqrt(n2oPressure)) / (ratioConstant * Math.sqrt(fuelPressure));
var finalFuelJet = Math.sqrt(fuelArea);
// Format results to standard jet sizes (thousandths of an inch)
document.getElementById("n2oJetResult").innerHTML = "." + Math.round(finalN2OJet).toString().padStart(2, '0');
document.getElementById("fuelJetResult").innerHTML = "." + Math.round(finalFuelJet).toString().padStart(2, '0');
document.getElementById("resultArea").style.display = "block";
}