Nitrous oxide (N₂O) isn't magic — it's a chemical oxygen carrier. At room temperature it's a stable liquid under pressure (~750 psi in the bottle). Injected into the intake, it flashes to gas and — critically — decomposes at around 570°F during combustion, breaking into nitrogen and free oxygen. That oxygen is what lets you burn more fuel. The horsepower comes from the extra fuel, not the nitrous itself.

Why bother? Because ambient air is only 21% oxygen. Nitrous, once decomposed, delivers roughly 36% oxygen by mass — a ~70% richer oxidizer stream. As a bonus, the phase change from liquid to gas cools the intake charge by 60-75°F, densifying it further. That's why a "100 shot" can actually make 110-120 hp of measurable gain.

Dry systems inject only nitrous into the intake tract; the extra fuel comes from the OEM injectors, which the ECU commands to open longer (via a MAP signal spoof or piggyback). Simple, clean install — but you're relying on the fuel pump and injectors to have enough headroom. Best for shots under 75 hp.

Wet systems inject nitrous and supplemental fuel together through a dedicated fogger nozzle or plate. The fuel/nitrous ratio is set mechanically by jet sizing, independent of the ECU. This is what you need for 100+ hp shots because you're not asking the OEM fuel system to do something it wasn't designed for.

Rule of thumb: Nitrous-to-fuel mass ratio should be about 5:1 to 5.5:1 for gasoline (compared to air-to-fuel's ~14.7:1). For a 100 hp shot flowing roughly 0.75 lb/min of nitrous, you need about 0.14 lb/min of extra fuel — call it 8.4 lb/hr, or a #45 jet at 43 psi.

Real-world example: A Fox-body Mustang 5.0 with a 150-shot ZEX wet kit. Bottle at 900 psi, nitrous jet #63, fuel jet #34, timing retarded 4° from the base map. The car makes ~270 rwhp naturally and jumps to ~410 rwhp on the button. Timing retard is non-negotiable — nitrous accelerates flame speed, and running stock timing on a 150 shot will hammer pistons like a jackhammer. General rule: retard 2° of ignition timing per 50 hp of nitrous.

Failure modes are dramatic: lean-outs melt piston crowns (fuel solenoid opens late, nitrous solenoid opens on time), and detonation snaps ring lands. Always use a bottle pressure gauge, a purge valve, and a WOT-only activation switch.