NOS Nitrous Oxide Systems Technical Information
What is NOS? NOS is an abbreviation for Nitrous Oxide System and also the brand name for the company Holley NOS. NOS is quite often incorrectly used to describe Nitrous Oxide.
What is Nitrous Oxide?
For the purposes of automotive use, Nitrous oxide when in its desired state of compressed liquid can be thought of as an extremely dense form of oxygen.
Chemical Properties of Nitrous Oxide
Nitrous oxide molecules consist of 2 atoms of nitrogen bonded to 1 atom of oxygen. By weight it is 36% oxygen, whereas the oxygen content in air is only 23.6%. At 70° F it takes 760 PSI of vapour pressure to hold nitrous oxide in liquid form. When liquid nitrous is released from the pressure it's contained at in a bottle, it drops from 760 PSI + to 14.7 PSI (normal atmospheric pressure), very quickly and in the process it boils and rapidly expands, resulting in a substantial temperature drop as nitrous boils at 129.1°F below zero.
The Effects Of Nitrous Oxide Systems On Intake Temperatures
Cooler intake air is denser and therefore contains more oxygen, which will allow more fuel to be burned and in turn make more power. Just a 10 degree drop in temperature has the potential to increase an engines power by up to 1.5%. Nitrous oxide boils at -129°F and it begins to do that as soon as it’s injected into the intake manifold. To boil, the nitrous has to absorb heat from the intake charge and in so doing has the potential to reduce the intake air temperature by up to 80°, which means that if we were dealing with say a 400 hp engine, we could see a gain of over 30 hp from the cooling effect alone and as a bonus, this cooling effect also helps the engine stay below the detonation threshold.
To achieve such a good cooliing effect the nitrous must be injected as a liquid. Only The Wizards of NOS 'Street Blaster' Systems are capable of injecting such dense liquid as to take maximum advantage of this effect.
The Affect Of Adding Nitrous Oxide To An Engine;
Activating a NOS nitrous oxide system adds nitrous oxide & fuel to the original inlet charge and although the nitrous oxide itself does not burn, it is an oxidiser which provides more oxygen to allow the additional fuel to be burned, and therefore produce more power. At 565 degrees F (less than the temperatures of normal combustion), the molecules of nitrous oxide break down, releasing the oxygen atoms from the nitrogen atoms. Once free from the nitrogen, the oxygen supports the combustion of the additional fuel, while the released nitrogen suppresses detonation. The increased amount of oxygen & fuel in the combustion chamber results in the assorted molecules being more tightly packed than normal, which leads to a quicker burn rate, that requires less timing advance for optimum results. Without retarding the timing appropriately, the quicker burn rate would cause peak cylinder pressure to occur too soon and this would lead to detonation and engine damage.
Up to a point, adding nitrous oxide to an engine will reduce the risk of detonation (especially on forced induction engines) but after that point when larger power increases are wanted it will increase the risk. One of the reasons for this is the extra heat generated and the easiest way to overcome this being a problem, is to add excess fuel which will act as a coolant. All nitrous systems are supplied with rich jetting to give you a safe starting point, which means this issue is already dealt with to some extent and as long as an engine is not pushed to the extreme, running slightly richer should be all you'll need to control detonation. Whilst running richer than optimum will reduce the power output slightly, the advantage of raising the detonation limit will allow more nitrous to be used to get more power more safely.
With all the above in mind it is obviously essential to supply the engine with precise amounts of additional fuel, to match the amount of nitrous oxide being added (to ensure the engine doesn’t run lean) and to retard the timing to an optimum setting, to achieve successfully and reliable results. When all three (fuel, nitrous and timing) are controlled accurately, your engine can safely and reliably generate exceptional power increases.
How a nitrous oxide system works
The most essential part of a nitrous oxide injection system is the supply cylinder containing pressurised liquid nitrous oxide. This cylinder is connected by means of a delivery hose to a normally closed electric solenoid valve. The control solenoid valve (which is usually mounted in a cool area under the bonnet), is opened and closed by means of a sequence of two switches, one activated by the throttle and the other a manually activated arming switch. A fuel solenoid (controlled by the same switches as the nitrous solenoid), takes a feed from a 'T' piece, which is tapped into the fuel delivery line. The nitrous oxide and fuel that is to be delivered to the engine is supplied via two delivery pipes, to one or more injectors mounted in the inlet manifold.
The Difference between Wet & Dry Nitrous Systems
A 'wet' nitrous system delivers nitrous and fuel under the control of the nitrous system. In contrast a 'dry' nitrous system only controls the delivery of the nitrous oxide, while the fuel is delivered via the existing fuel injection system by increasing either delivery pressure or by extending the injector open time. Single injector dry systems are sometimes referred to as 'dry manifold system' because the additional fuel does not pass through the manifold as it does with a single injector wet system.
|A typical wet system||A typical dry system|
Take a look at some of our typical wet nitrous kits here
And our dry nitrous kits here
Nylon Lines vs. Braided SS
IMPORTANT: The purpose of the following information is not to deny the ‘general’ qualities of stainless steel braided hose, it is only for the two following reasons;
1) To make the facts known as to why ‘our’ nylon pipe, is better suited to nitrous use for optimum results.
2) To dispel all the ill informed claims that ‘our’ nylon pipe is inferior to braided pipe.
Before considering the following information, please consider the following facts. It is now almost universally accepted, that WON Pulsoids are vastly superior to ‘generic’ solenoids, as supplied in all other brands of nitrous kits. Does it therefore not make sense that we’d also supply the ‘best’ pipe for the job?
We'd also like to point out that when higher flow rates are required than the nylon is capable of flowing, we do supply braided hose between the bottle and nitrous solenoid.
Misconception 1) Braided hose can handle more pressure.
Truth; At ambient temperatures under 30 degrees that is not the case, as ‘our’ nylon pipe is capable of approx. 6,000 psi. However, even if it were true, what is the point of using pipe that is capable of handling more pressure than it will ever be subjected to? Furthermore, as it is very dangerous to your engine to supply it with nitrous above 1,000 psi, it would be safer to use a pipe that would burst just above that pressure, to act as a safety switch/fuse and warning indicator.
Misconception 2) The stainless steel outer braid shields the hose contents from heat.
Truth; The outer braid actually ‘conducts’ and ‘holds’ heat in closer proximity to the contents, than would be the case without it. This misconception has lead to some extreme instances, where people have secured the hose to the exhaust system, which has vaporised the liquid nitrous into gas and resulted in NO extra performance.
In contrast, WON pipe is made of nylon that is a very good ‘insulator’ and therefore ‘does’ shield the contents from heat.
Misconception 3) Braided hose is indestructible.
Truth; The interwoven strands are the only protection the inner hose has but if only ‘one’ strand gets damaged, the whole hose integrity is lost, because the inner plastic (PTFE) hose has no strength. Contrary to people’s expectations, it is very easy to snag more than one strand on a sharp edge, especially when routing the hose through the car.
Misconception 4) All braided hose is high flow
Truth; Braided hose end fittings go ‘inside’ the hose and the bore of these fittings is much smaller than the bore of the hose itself and as a consequence the flow rate is much lower than the pipe bore along would support.
Detrimental consequences of this hose assembly design/technique are as follows;
1) The steps created by the fittings cause the nitrous liquid to phase change to gas, as it passes through the fittings.
This does not apply to WON nylon pipe, as the fittings are external to the pipe.
2) The much larger bore of the braided hose acts as a large reservoir for the initial gaseous (not liquid) nitrous build-up prior to activation, that will result in a ‘dramatic’ loss in performance unless it’s purged to atmosphere and wasted before every operation.
This is not a problem with WON nylon pipe, as the ‘very’ small bore means there is minimal build-up so purging (waste) is not needed to achieve optimum results.
3) In competitor's kits the braided hose is supplied in a fixed length, which means the surplus hose has to be coiled up, which results in an even bigger unnecessary waste of nitrous.
WON nylon pipe can be cut to the ‘minimum’ length required to avoid this waste.
For even more reasons to use WON nylon pipe rather than braided hose, please read the following forum thread;
Spark plugs & nitrous performance
The simplest way to appreciate if a spark plug is suitable for nitrous or not is to consider the following; When you add nitrous to an engine you’re subjecting the spark plug to more heat and as a consequence it will be more likely to melt. The more metal that the spark plug consists of, the more metal there is to melt. By minimising the length and number of electrodes, you are reducing the amount of metal that can melt and lead to the destruction of your engine. Consequently long ground electrodes (as in the case of projected nose plugs) and multiple ground electrodes (both of which are commonly used as standard in most cars), are to be avoided at all costs. Also to be avoided (but not for the same reason) are surface discharge plugs, which although they seem ideal for nitrous (due to not having any ground electrode), are most certainly not suitable, because the spark gap is too big and can’t be reduced.
The vehicles standard he
at range plug should be increased by one step for every 50 HP increase. In the case of NGK this would mean changing a 6 for a 7 etc. and where possible a plug with the letters ECS after the number are best suited to nitrous use as they have a shorter than normal ground strap.
Why Not Pure Oxygen?
The simple and most relevant answer is because we couldn’t get enough into the engine for it to be as effective as nitrous oxide. Air has only 23.6% oxygen by weight, the rest is made up largely of nitrogen. Although nitrogen does not aid the actual combustion process it does absorb heat, as well as damping what would otherwise be a violent explosion, rather than a controlled burn. When you add nitrous, it has 36% oxygen with the rest being nitrogen. So the more nitrous oxide you add, the less percentage of nitrogen is available to absorb heat. That’s one of the reasons why adding more nitrous increases the heat of combustion very rapidly. If we were to add pure oxygen (which has been tried), the percentage of nitrogen would progressively decline to a much greater degree than with nitrous, as more and more oxygen was added. Consequently an engine wouldn’t be able to handle much pure oxygen before the increase in heat lowered the detonation level to unusable levels. Furthermore, oxygen can only be ‘readily’ stored in a compressed ‘gaseous’ form, without being stored in a special cryogenic thermos cylinder (a cylinder within a cylinder with a vacuum between the two walls) and as a gas it loses the cooling effect that nitrous offers by being available as a liquid. Adding the oxidiser as gaseous oxygen would displace more air than adding nitrous in liquid form, resulting in a lower total power capability. In other words; by using nitrous oxide we can squeeze in more oxygen atoms in a more beneficial form, containing substantial amounts of detonation suppressing nitrogen, than would be the case with gaseous oxygen.