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Nitrous Oxide Basics

by Bob McClurg

Nitrous oxide is recognized as one of the most flexible, affordable, and reliable forms of power adder that exist for automotive engines. Just about any vehicle can experience a noticeable increase in power and performance with the addition of a properly engineered nitrous oxide injection system.

The most basic type of nitrous oxide injection is defined as a plate system, where nitrous oxide and fuel are simultaneously added through tubing mounted to a plate, which is sandwiched between the existing carburetor/throttle body and the inlet manifold.

The nitrous oxide plate itself looks like a standard 1/2- to 1-inch-thick 4-barrel carburetor spacer plate. In fact, I wouldn’t be surprised if that’s what its inventor originally adapted it from. Then along came the addition of fuel and N2O jet ports accompanied by brass, aluminum, or stainless-steel spray bars. They feature a series of finely drilled holes running either north/south, or east/west, depending on carburetor type and throttle linkage design. When you activate the N2O system, this combination of gasoline and N2O gets mixed with the atomized fuel from the carburetor, and is distributed throughout the intake runners to the combustion chambers. Once lit, the byproduct is an instant and dramatic burst of power!

nos plate

Over the past 40 years, the crossbar-design N2O plate has been accepted as the standard of the industry

Not all single-stage carburetor plates are alike. In an ongoing attempt to improve on the basic 40-year-old design and perhaps gain a larger market share, some manufacturers (like Nitrous Express and ZEX Nitrous Products) have introduced advanced design nitrous plates, such as the ZEX Perimeter Plate, as standard equipment.

You may be asking, “Why a fuel port when there’s already a carburetor?” The most obvious reason is the power adder concept itself, keeping in mind that N2O enters the intake runners of an internal combustion engine at 127 degrees F.

The molecular density of N2O is such that you need an additional shot of fuel—using a properly matched gasoline jet—to offset the nitrous charge and fire the cylinder. Otherwise, you have to run a huge carburetor jet, which affects overall fuel mileage and driveability under normal driving conditions.

Nitrous Oxide and Fuel Jets

Nitrous oxide and fuel jets are both power-matched to complement a particular N2O kit or application. For example, with Edelbrock Corporation’s 50- to 100-hp Universal Big-Block Chevrolet Square Flange Kit (PN 70001), the N2O and fuel jets (three per grouping) are perfectly matched to their counterparts, such as: Nitrous/Fuel 38/38 = 50, 46/46 = 75, 57/57 = 100 hp.cnc manufactured

N2O and fuel jets are both CNC manufactured from either brass or stainless-steel and are drilled, or inner-contoured, per each N2O manufacturers’ specifications in order to arrive at what is perceived to be the ideal rate of flow. Jet size ranges from .014 to .136 inch on average. Per application, a series of pre-selected jets are typically included in a single-carbureted street N2O kit.

However, that may not always be the case. For example, with Nitrous Supply’s Power Star Holley carburetor nitrous kit for the carbureted 350-ci small-block Chevrolet (PN 8001), jetting favors the nitrous side of the equation: Nitrous/Fuel 42/47 = 75, 47/53 = 100, 55/61 = 125, 63/71 = 150. Always pay close attention to the manufacturer’s recommended jet specification sheet.

As a rule, nitrous jets are all CNC machined out of brass or stainless steel. Why both? Originally, it was to visually determine the difference between fuel (brass) and N2O (stainless). However, in recent years some N2O kit manufacturers have exclusively switched to precision-machined stainless steel jets to avoid corrosion issues. Sized or upgraded nitrous and fuel jets are available in master jet packs through participating N2O kit manufacturers and/or retailers.

Nitrous Oxide Solenoids

Simply put, a solenoid is an electrically activated on/off valve that controls fuel flow (which could be either gasoline or alcohol) and nitrous oxide flow at the flick of a switch. When it comes to actual construction, some solenoids are manufactured out of stainless steel or aluminum. The higher quality the materials, the less trouble you’re going to have in the long run, so it is always wise to check with the manufacturer first when buying a single-stage N2O kit.

If there is such a thing as a heart and soul of a solenoid, it is the electric coil used to open and close the fuel orifice (see the illustration on page 14). Generally speaking, the coil is designed to operate at 20 percent of the maximum fuel operating pressure at WOT. The duty cycle of a high-pressure solenoid (which would always be the nitrous side) is generally no more than 30 seconds at 33 percent. Low-pressure solenoids (typically used on the fuel side) have a duty cycle duration of 5 seconds at 50-percent duty cycle.

Amperage draw varies. Most single-stage kits feature 8.5- to 10-amp nitrous and 4-amp fuel solenoids, which combine for a system draw of 12 amps. But a higher amperage draw is going to allow the coil to open at a higher pressure. However, the longer a coil is open, the more amperage it draws, and the hotter it gets.

Orifice size is also very important because it dictates flow capacity. Think of a solenoid as a huge jet. You want the solenoid to flow at maximum PSI. In fact, its flow rating should always be larger than the combined metering jets throughout the rest of the fuel system.

Plunger quality and seal quality, which control the hit (or intensity) is also very important and has a lot to do with the longevity of the solenoid(s). Again, be sure to consult with your manufacturer of choice before selecting a kit. Remember, a bargain kit may not be such a bargain when you balance it against long-term component reliability.

Never use the wrong solenoid for an application. That is the quickest way to cause serious damage to an engine. Generally speaking, fuel and nitrous solenoid mounting brackets on a single-stage-plate N2O kit typically have the fuel solenoid located at the left rear carburetor stud, in the general vicinity of the fuel supply line and the N2O solenoid being located at the left front carburetor stud. Mounting brackets vary depending on the level of sophistication and cost of the kit in question. Of course, you can always upgrade. Just to cite one example, Edelbrock Nitrous’ optional CNC-machined Two-Solenoid Bracket(s) for square-flange Edelbrock Performer, Holley 4500, and Dominator carburetors are some of the nicest solenoid brackets I’ve seen.

When installed and tuned correctly, a basic nitrous oxide plate system can provide a reliable and safe performance boost. The nitrous system is driver-activated and, when wired according to the manufacturer’s instructions, is only functional when the engine is operating at wide-open throttle. A properly jetted system does not push the engine beyond its capabilities, and should provide an entertaining and satisfying performance boost.

When installed and tuned correctly, a basic nitrous oxide plate system can provide a reliable and safe performance boost. The nitrous system is driver-activated and, when wired according to the manufacturer’s instructions, is only functional when the engine is operating at wide-open throttle. A properly jetted system does not push the engine beyond its capabilities, and should provide an entertaining and satisfying performance boost.nos system2

Nitrous Oxide Systems’ non-adjustable Powershot N20 kit (PN 05001NOS) for the Holley flange, and Q-Jet–type spread-bore flange (PN 05004NOS) offer up to 125 hp at the touch of a button. Note that there is also a Powershot Universal kit application (PN 05000NOS). For those who want more power and controllability, there’s the 100-125-150-hp Super Powershot nitrous kits available in standard Holley 4V flange (PN 05101NOS), Q-Jet-type spread-bore flange (PN 05104NOS), and even a Holley 2300 2-barrel-flange application (PN 051056NOS).


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