A NOS tank is a pressurized bottle filled with nitrous oxide (N₂O) that connects to a car’s engine to deliver a quick burst of extra horsepower. “NOS” originally refers to Nitrous Oxide Systems, a specific brand, but the term has become shorthand for any automotive nitrous setup. The tank itself is just one piece of a larger system, but it’s the most visible and recognizable component, especially after the Fast and Furious franchise made it a pop culture icon.
How Nitrous Oxide Boosts Engine Power
Nitrous oxide works because of a simple chemical trick. When N₂O is heated to about 570°F inside an engine’s combustion chamber, it splits apart into nitrogen and oxygen. That extra oxygen allows the engine to burn more fuel per combustion cycle, and more fuel burned means more power. A basic nitrous kit can add anywhere from 50 to over 300 horsepower depending on the setup.
There’s a bonus effect, too. When liquid nitrous oxide vaporizes as it enters the intake, it drops the temperature of the incoming air significantly. Cooler air is denser, which packs even more oxygen into each cylinder. So you get a power increase from two directions at once: the oxygen released from the N₂O molecules and the denser intake charge from the cooling effect.
What the Tank Looks Like and How It’s Built
Most automotive nitrous tanks are cylindrical bottles made from aluminum or steel, typically holding 10 to 15 pounds of liquid nitrous oxide. They look similar to a small scuba tank or a CO₂ cylinder. Inside, the nitrous sits under pressure as a liquid, typically between 900 and 1,000 PSI at the ideal operating temperature. The bottles are engineered to handle much more than that. Working pressure ratings commonly reach 1,800 PSI, and burst discs (safety valves designed to release pressure before catastrophic failure) are rated around 2,200 to 3,000 PSI.
The tank connects to the rest of the system through a valve at the top, which feeds into high-pressure lines running to the engine. A siphon tube inside the bottle reaches down to the bottom, ensuring liquid nitrous (not just gas) gets pulled into the feed line when the system is activated.
The Full System Beyond the Bottle
The tank stores the nitrous, but several other components control how it reaches the engine. Electrically operated solenoids act as gatekeepers, opening and closing in milliseconds when the driver hits a button or a throttle switch triggers the system. Feed lines carry the pressurized nitrous from the bottle to the engine bay. At the engine, either a spray plate (mounted between the intake and throttle body) or individual nozzles (one per cylinder) atomize the nitrous into the airstream.
Calibrated jets, which are small discs with precisely sized holes, control exactly how much nitrous flows through. Swapping to a larger or smaller jet changes the power output of the system. This is how racers tune their setup for different levels of boost.
Wet Systems vs. Dry Systems
Since extra oxygen needs extra fuel to match, nitrous kits come in two configurations. A “wet” system delivers both nitrous and supplemental fuel through the same plate or nozzle. It uses a dedicated fuel solenoid and its own fuel supply, with jet sizes calibrated to keep the air-fuel ratio safe. Wet kits are popular on carbureted engines and many fuel-injected setups because they don’t require reprogramming the engine’s computer.
A “dry” system sprays only nitrous. It relies on the engine’s existing fuel injectors and computer (ECU) to add the extra fuel. The ECU detects the change in airflow or receives a signal from the nitrous activation switch, then increases injector output to compensate. More advanced ECU setups can pulse the nitrous solenoids, add progressive delays, and fine-tune the delivery based on parameters like RPM and throttle position. Dry systems are cleaner to install but require a capable engine management system to work safely.
Why Bottle Temperature Matters
Nitrous oxide pressure is directly tied to temperature. On a cold day, bottle pressure drops, which means less nitrous flows into the engine. On a hot day, pressure climbs. NOS systems are designed to operate with bottle pressure between 900 and 1,000 PSI, and straying outside that window creates problems.
Low bottle pressure is especially harmful. Less nitrous enters the engine, but the fuel side of a wet system still delivers the same amount of fuel regardless. The result is an overly rich mixture that kills power instead of adding it. This is why many serious setups include a bottle heater, an electric heating element that wraps around the tank and warms it to about 130°F. A built-in pressure switch automatically shuts off the heater once bottle pressure hits roughly 975 PSI, keeping things in the optimal range. Between runs, the heater also recharges the bottle’s pressure, since each use cools the contents as liquid nitrous vaporizes and exits.
Automotive-Grade Nitrous vs. Other Types
Not all nitrous oxide is the same. Medical-grade nitrous (U.S.P.) is the pure form used for dental anesthesia and as a propellant in whipped cream cans. It isn’t sold to the general public. Automotive-grade nitrous, sometimes labeled “Nitrous Plus,” contains trace amounts of sulfur dioxide specifically added to discourage recreational inhalation. The sulfur dioxide makes it unpleasant and unsafe to breathe, which is the entire point. For engine use, these trace additives have no meaningful effect on performance.
Refilling the Tank
Nitrous tanks are refillable, not disposable. When the bottle runs empty, you take it to a speed shop or racing supplier that offers fills. Pricing typically runs around $8 to $10 per pound, with small surcharges common. A standard 10-pound bottle costs roughly $80 to $100 to fill. How long a fill lasts depends entirely on how much nitrous you use per activation and how often you hit the button, but a 10-pound bottle on a moderate 100-horsepower shot might last 8 to 10 quarter-mile passes.
What Can Go Wrong
Nitrous oxide itself doesn’t damage engines. The problems come from the conditions it creates. The most common cause of nitrous-related engine failure is detonation, which happens when the fuel mixture ignites uncontrollably instead of burning in a smooth, controlled wave. This is almost always caused by running too lean (not enough fuel for the extra oxygen), using fuel with too low an octane rating, or having too much ignition timing advance.
A properly tuned nitrous system with correct jet sizing, adequate fuel supply, and appropriate ignition timing is reliable. Most horror stories trace back to people installing bigger jets than their fuel system can support, or skipping the tuning process entirely. Engines with forged internals handle nitrous better than stock components, which is why most builders recommend keeping power additions modest on a factory engine.
Legal Considerations
Nitrous legality varies by state and depends on how the system is configured. In Virginia, for example, it’s a misdemeanor to drive on public roads with a connected and readily accessible nitrous system. The bottle must be physically disconnected from the delivery system to be legal on the street. Many other states have similar rules, often requiring the bottle valve to be closed or the feed line to be disconnected when driving on public roads. At the drag strip or on a closed course, there are generally no restrictions. If you plan to run nitrous on a street-driven car, check your state’s specific vehicle code before installation.