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Nitrous: Pray or Spray?
Nitrous oxide systems have been a part of the performance scene for many years now, but thanks (or no
thanks) to the Fast & Furious franchise this staple of hot rod performance and power has been glorified
to mythical status and as such has become the subject of some misunderstanding and ill-conceived
information. So for this week’s article let’s delve into the realm of N2O!
Let's Cut to the Oxygen
To begin we should have a good understanding of the main component in question, oxygen. Oxygen in
the atmosphere only makes up about 23% (measured by mass) of the total components of the air we
breathe but is effectively the only component within the atmospheric air mix that does an engine any
good. Oxygen provides the necessary oxidizer for fuel to combust and burn. Without it a fire would go
out, such as with the use of a fire extinguisher where the effect is flooding the area to remove oxygen
and put out the fire. The same is done with welding gas on MIG and TIG welders to flood the area of the
weld and prevent oxygen from oxidizing the molten hot bead. An oxidizer can be simply defined as any
chemical necessary for a combustable to burn or chemically react.
Introducing... 50% More O2!
Nitrous oxide does effectively the same thing as a turbocharger or super charger, in fact it’s so similar
that it’s been referred to as chemical charging in the past. The similarity between nitrous oxide and
forced air induction is that both methods work to increase the oxygen capacity of the cylinder. However
nitrous oxide does this in a different way entirely. While turbo chargers and super chargers force
more air into the cylinder increasing total mass of oxygen, nitrous utilizes the very nature of its higher
chemical density of oxygen from the start. Unlike atmospheric air that is 23% Oxygen, nitrous Oxide
(chemically shown as N20) has 36% oxygen by weight. By injecting this into the air intake stream we can
increase the cylinder oxygen mass. Additionally since the N2O is stored under pressure in the bottle as a
liquid and sprayed into the motor as a gas, the state change from liquid to gas absorbs considerable heat
energy which is very desirable to further cool the atmospheric air entering the engine as well and reduce
The Simple Way
Nitrous in and of itself is not flammable, explosive, or unstable. Only when fuel is added to it can
it provide the gains we see glorified in so many movies. Just like the normal air fuel mix, nitrous
injected must have a matching fuel mass to maintain the ideal air fuel ratio. In ‘wet’ nitrous systems an
additional nozzle is attached to the fuel rail to then join the injected nitrous oxide into the intake tract.
This provides the added oxygen and fuel in a proper mix to increase power. ‘Dry’ nitrous systems do not
add this fuel by virtue of an additional fuel nozzle but instead rely on engine management to add the
additional fuel. This can be done by either a trigger input to the EMS to add fuel based on the quantity
of nitrous injected or in many ‘homebrew’ methods the nitrous is injected ahead of the MAF sensor so
that the MAF can detect the added oxygen and consequently add appropriate fuel. Unfortunately this
later method tends to be less precise, although since it is less costly and easier to install it’s becoming
more common to see it in the aftermarket.
Top, Bottom, & Longetivity
Proper use of nitrous depends on the application in question but commonly you’ll find more moderately
built engines use nitrous on the top end to help maintain power where a smaller turbo might start to
fall out of efficiency. For larger, more aggressive engine builds with larger turbo chargers, nitrous can be
used to help offset the lag that a larger turbo charger generally creates. Either way the added cylinder
pressure is something that should be considered regardless of engine type and build so that engine
longevity can be maintained.
Kits Rated by HP
Nitrous kits are typically rated by the horsepower they provide to the engine and you’ll see them
marketed as “50 shot” or “100 shot” which again is the measure of the BHP increase you’re likely to
see. Refilling nitrous tanks can be fairly cost effective depending on where you are but per pound will
run between $5.00- $7.00. Tank size can vary and amount of nitrous used per spray depends on you as
a driver so refill intervals will vary wildly from one person to another. Lately more convenience features
have been offered such as remote bottle opening via electric motor as well as bottle heaters to keep the
N2O from getting too cold during prolonged use and reducing cylinder pressure. These added features
help to keep nitrous as a useful and easy to operate performance product.
Further questions??? Post up in the comments!
Robert Lucky Arnold
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