Nitrous Jet Selection Calculator

Flow through a fixed jet orifice scales with the square root of the pressure pushing fluid through it, so a bottle running at a higher pressure than the 900 PSI reference the jet number was sized against will actually flow more nitrous per hour through that same jet -- and a bottle at lower pressure flows less. Because bottle duration depends on how fast the bottle actually empties, this calculator uses that pressure-corrected flow rate rather than the idealized reference-pressure figure to estimate duration and passes per bottle.

A wet nitrous system injects both nitrous and additional fuel together at the nozzle, so it needs its own dedicated fuel jet sized to keep the air-fuel ratio safe under the added oxidizer. A dry system injects only nitrous and instead relies on the engine's ECU to add fuel through the injectors, so there is no separate physical fuel jet to size -- which is why this calculator reports a fuel jet size of zero whenever Dry is selected.

E85 contains a much higher percentage of ethanol, which has a lower energy density than gasoline and burns at a different stoichiometric air-fuel ratio, so reaching the same safe mixture under a nitrous shot requires flowing meaningfully more fuel by weight than gasoline would need for an equivalent horsepower gain. This calculator applies a higher brake-specific fuel consumption figure when E85 is selected to reflect that difference.

No -- jet numbering scales and actual flow rates vary by manufacturer (NOS, ZEX, Nitrous Express, and others all use different orifice-to-number mappings), so treat this calculator's jet numbers as a rough starting estimate to cross-check against your specific kit's own flow chart. Final jetting should always be verified with a wideband air-fuel ratio gauge under real load, not selected from a calculator alone.

Nitrous oxide raises cylinder pressure and combustion temperature substantially, which increases the risk of detonation (uncontrolled, damaging pre- ignition) at a given ignition timing setting. Retarding ignition timing reduces peak cylinder pressure during the critical part of the combustion event, so larger shots -- which raise cylinder pressure more -- call for more timing retard as a safety margin against detonation.