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What is NOS and how does it work?

Ashok George  | Updated: May 28, 2013, 03:29 PM IST

Too fast too Furious final race

Remember that little red button that Brian presses to keep up with Dom's Charger in the last scene of the Fast and the Furious? We've all used it in all of the Need for Speed games since Underground. We know it as NOS. For the uninitiated, it stands for Nitrous Oxide System. NOS of course is just a brand. But what is a nitrous injection system? Quite simply it is a way to give your engine a brief few hundred horsepower boost when you need it. But how does the nitrous boost work?

Everything needs oxygen to burn. This is true whether you're burning firewood, paper, petrol or aviation fuel. The more oxygen you supply, the more efficient your combustion is. One way to increase oxygen content is to force more air into the combustion chamber which will allow the fuel injection system to increase the amount of fuel being injected, hence making a bigger "bang" possible. But what if you want still more power. This is where nitrous oxide comes in. The regular air we breathe contains a little over 20 per cent of oxygen. In an internal combustion engine, at 20 percent oxygen, there is only so much fuel you can burn. So how do you increase oxygen content in the combustion chamber? Nitrous oxide of course!

There are two kinds of nitrous systems – wet and dry.

A dry nitrous oxide system injects nitrous oxide into the intake manifold. When the nitrous oxide is introduced into the intake manifold it cools down the air that is being inducted. This causes a rise in air density which is picked up by the sensors in the intake and conveyed to the ECU. The ECU then supplies more fuel to the injectors. When the mixture of air fuel and nitrous gets to the combustion chamber, the high ambient temperature causes the nitrous oxide to break up into nitrogen and oxygen (one oxygen atom per every two nitrogen atoms). This allows the mixture to burn more efficiently. It also allows the fuel mixture to be richer leading to a bigger "bang". The nitrogen that is generated is merely let out with the rest of the exhaust gases. The problem with running a dry nitrous system is that it is hard to tune the stock fuel injection system to adapt to when you're using nitrous. You will need stronger injectors that won't pack up under the high injection pressure required and a fuel pump that will be able to supply that kind of pressure as well.

A wet nitrous oxide system sprays not only nitrous oxide into the intake manifold, there is a secondary jet that injects fuel as well. When nitrous is activated, the jets in the intake manifold spray both nitrous oxide and fuel. The extra fuel makes for a super rich mixture which the extra oxygen from the broken down nitrous oxide helps ignite. Hence more power.

But there is a problem with either of the nitrous systems. With great power comes great mechanical stress. Remember what happens when Brian's Eclipse is racing against Dom's RX-7 in the first race in the movie? Too much nitrous quite literally kills his engine. And you can see him rolling back to the starting line with smoke billowing out from under his hood. The rule of thumb is that you can keep the nitrous going for a maximum of 15 seconds at a stretch. Oh, and if you're expecting to see blue flames from your exhaust when you push the tiny red button, you're mistaken. That my friends is the most famous myth about nitrous.

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