Selecting The Right Nitrous Jet For High Fuel Pressure

Sizing a nitrous jet with high fuel pressure is a complex process that requires careful consideration of several factors. The jet size is determined by specific nitrous and fuel pressures, as well as the desired horsepower level. The relationship between fuel pressure and jet size is directly proportional, meaning that increasing fuel pressure will result in a larger jet size. However, it's important to note that this also depends on the type of fuel system in use. For instance, a closed-end or dead-head nitrous fuel system experiences fuel pressure creep due to the fuel pump pushing against a closed valve. This results in a significant pressure drop when the nitrous system is activated. To accurately set the fuel pressure, a high-quality gauge is necessary to measure fuel pressure under simulated load conditions. Additionally, the air-to-fuel ratio plays a crucial role in determining the nitrous jet size. While opinions vary, it is generally recommended to run slightly rich, with an air-to-fuel ratio between 11.5:1 and 12.5:1 for engines up to 250 hp. For higher horsepower engines, the ratio should be richer, such as 10:1 for a smaller motor or 11.5:1 for a bigger engine.

Characteristics and Values Table for Sizing a Nitrous Jet with High Fuel Pressure

Nitrous oxide jet calculator

A Nitrous Oxide Jet Calculator is a useful tool for those wanting to calculate fuel jet sizes and horsepower from nitrous and fuel pressure and nitrous jet sizes. This is particularly helpful for those who don't want to manually calculate the nitrous/fuel jet sizes and combinations.

Air/Fuel Ratio

Most sources recommend running slightly rich, generally between 11.5-12.5:1, but this is not a universal agreement. Some sources recommend going even richer under certain circumstances. At 250 hp and under, you can run the same as the engine's air/fuel ratio. However, at 450-500 hp, run 11.5:1 as a safety factor. The exact air/fuel ratio can be adjusted according to engine displacement.

Bottle Temp to Bottle Pressure Ratio

Raising nitrous-bottle pressure makes the system perform harder off the line but at the expense of an inconsistent taper-off at the top. To avoid problems, it is recommended to stick to the system manufacturer's recommended bottle operating pressures, which is usually 900-1,000 psi. The pressure will drop during a run, but it should still have 880-900 psi at the end.

Nitrous Oxide Horsepower Chart

Nitrous Express provides jetting charts for single and dual nozzle jetting by fuel pressure, as well as a nozzle selection guide. These charts cover all makes and models.

Fuel Jet Hi-output Pump

This is just a guideline, and variables such as nozzle type and distribution block type can change a particular set-up. It is recommended to consult an engine builder for fine-tuning tips.

Air/fuel ratio

The air/fuel ratio is a crucial factor in determining the performance and reliability of a nitrous system. The optimal air/fuel ratio for complete combustion of gasoline (known as the stoichiometric ratio) is 14.7:1. However, gasoline engines typically produce maximum power at an air/fuel ratio of 12.5:1-13:1.

When using nitrous oxide, which is more oxygen-rich than air, the chemically correct air/fuel ratio becomes approximately 9.65:1. This ratio is calculated as 9.65 parts of nitrous to 1 part of fuel.

To prevent detonation and engine damage, it is recommended to add additional fuel beyond this chemically correct ratio, with an ideal range of 8:1-8.2:1. Running slightly rich (between 11.5-12.5:1) is generally recommended, but this is not universally agreed upon, and some sources suggest even richer ratios under certain circumstances. For example, at 250 hp and under, the same air/fuel ratio as the engine can be used, while at 450-500 hp, a ratio of 11.5:1 is recommended as a safety factor.

The exact air/fuel ratio can be adjusted based on engine displacement. For instance, a smaller engine may require a richer mixture, such as a ratio of 10:1. Additionally, the ratio of nitrous power to engine power should be considered, as it affects the accuracy of O2 sensors used for tuning.

The nitrous-to-fuel ratio in most commercial kits is typically set in the 5.5-6.0 range, providing a generous safety factor. Increasing this ratio to 7.0-8.0 will generate more power, but it is important to monitor the air/fuel ratio to ensure it stays within the optimal range. If the measured air/fuel ratio values are below 11.5-12.0 when the system is activated, a smaller fuel jet can be used to adjust the ratio.

The metering jets play a critical role in determining the amount of fuel and nitrous supplied to the engine. By selecting the appropriate jet sizes and maintaining the correct ratio of nitrous to fuel, optimal performance and engine reliability can be achieved.

Bottle temp to bottle pressure ratio

The relationship between nitrous bottle temperature and pressure is a critical factor in maintaining optimal performance in nitrous oxide systems. This is because the amount of nitrous delivered by the system is directly dependent on pressure, and any deviation from the ideal pressure can result in reduced power output or even damage to the engine.

Nitrous oxide is a gas at standard temperature and pressure, but when pressurized above approximately 735-750 psi, it becomes a liquid. This liquid form is far more dense and thus more potent as a power adder. Therefore, maintaining the ideal bottle pressure, typically around 900-1000 psi, is crucial for maximizing the system's effectiveness.

The temperature of the nitrous bottle has a direct impact on its internal pressure. As the temperature increases, so does the pressure, and vice versa. This relationship is not linear, and the specific pressure-temperature correlation depends on various factors, including the initial amount of liquid nitrous in the bottle and the ambient temperature. However, as a general rule, keeping the bottle temperature at around 85-92 degrees Fahrenheit will result in a pressure of approximately 950 psi, which is the sweet spot for most nitrous systems.

To achieve and maintain the desired bottle temperature and pressure, various methods can be employed:

• Using an electric bottle heater with a thermostat to keep the bottle at the optimal temperature.
• Utilizing a bottle blanket and an electric heating device to warm the bottle in cold climates.
• Applying a cold towel and ice to cool the bottle in hot weather.
• Storing the bottle in a container with warm water to quickly raise the temperature.

It is important to monitor both temperature and pressure to ensure they remain within safe and optimal ranges. While temperature can be measured with an infrared temperature gun, measuring the actual pressure with a nitrous pressure gauge is the most accurate method.

Additionally, it is crucial to never use an open flame to heat a nitrous bottle, as this can cause stress fractures and lead to a dangerous explosion.

Nitrous fuel pressure creep

To address this issue, it is important to set the nitrous fuel pressure by creating a system fuel flow. This can be achieved by using tools like the Zex kit, which includes a high-quality gauge to measure fuel pressure under simulated load conditions. Plumbing the Zex gauge in line with the same gas jet used in the nitrous system will allow for accurate fuel pressure adjustments.

Another way to stabilize fuel pressure in a nitrous system is to use fuel bleed fittings. Fuel bleeds help to speed up the flow of fuel when the solenoids are activated and prevent fuel regulator pressure creep. Without fuel bleeds, the regulators can creep up to the fuel pump pressure, causing issues such as over-ranging sensors and a rich nitrous hit at initial activation.

Additionally, maintaining the nitrous bottle at a consistent temperature is crucial for stable nitrous pressure. A bottle blanket or an electric bottle heater can help stabilize the bottle temperature, ensuring the desired pressure is maintained throughout the run.

By understanding and addressing nitrous fuel pressure creep, you can keep your nitrous engine healthy, powerful, and functioning optimally.

Jetting charts

Step 1: Choose the Right Chart Group:

Start by selecting the group of charts designed specifically for your nitrous system. This includes considerations such as the make and model of your vehicle, the type of nozzle, and the number of nozzles (single or dual).

Step 2: Match Your Fuel Type and Configuration:

Next, choose the chart that corresponds to your fuel type (gasoline or E85, for example) and your system configuration. This ensures that the jetting recommendations align with your specific setup.

Step 3: Determine Your Horsepower Level:

Decide on your desired horsepower level. This is an important factor in selecting the appropriate nitrous and fuel jet sizes.

Step 4: Select the Nitrous Jet:

Refer to the chart and find the row that corresponds to your desired horsepower level. Under the “N2O” column, you will find the recommended nitrous jet size.

Step 5: Choose the Fuel Jet:

On the same row as your desired horsepower level, look for the column that matches your fuel pressure. The fuel pressure is the pressure at which the fuel is supplied to the solenoid. Select the fuel jet size listed in this column.

It's important to note that jetting charts provide a baseline for your setup, but there may be variations depending on other factors. These factors include nozzle type, distribution block type, and engine characteristics. Always consult an expert or your engine builder for fine-tuning tips specific to your vehicle and setup.

Additionally, when working with nitrous systems, it's crucial to follow safety guidelines. Stick to the system manufacturer's recommended bottle operating pressures to avoid potential issues. The recommended bottle pressure is typically around 900-1,000 psi, but it can vary slightly between manufacturers.

Frequently asked questions