All About Nitrous Oxide
paul_huryk Mar 31 2006 - 4:47pm
I have to admit, I love Nitrous Oxide for use in dual purpose street cars. The reasons are simple:nitrous kits are cheap,it is easy to hide,and it is easy to tune and maintain. These reasons coupled with understanding how Nitrous works,and how to use it CORRECTLY make it a good performance booster.
Nitrous Oxide is a gas,but under pressure in a closed vessel,it is a liquid. Nitrous Oxide was first discovered in 1772 by Joseph Priestly,an English scientist. Nitrous Oxide's uses were not found until many years later when it was discovered it was a good anesthetic for medical use. Nitrous Oxide molecules consist of two nitrogen and one oxygen atom. In this molecule,oxygen accounts for 33% of the molecule and 36% of the molecule weight,compared to 23% content in the air we breathe. If you used pure gaseous Nitrous Oxide in your motor,you would gain about 40% more hp because of the increased oxygen content. Nitrous really shines when it is a liquid,it takes up much less space than the gas,plus it "cools" the intake mixture when it is injected. Nitrous takes up 8.7 cubic feet per pound as a gas at 70 degrees farenheight; at a liquid state you can stick 10.56 lbs into .133 cubic feet, that is a lot denser.
Nitrous adds power by adding extra oxygen in a compact form into an engine. Of course,to combust this extra oxygen you need a corresponding amount of extra fuel to accomplish this. Nitrous also cools down the intake charge,making it denser,thereby allowing more molecules per cylinder-making more power. There is no limit in how much liquid Nitrous Oxide you can get into a motor,but the motor itself can only take so much stress before it breaks something. Because nitrous increases cylinder pressure-a product of stuffing more oxygen into a cylinder,rods usually bend before anything else breaks. Running a Nitrous engine lean will cause "hot spots" on the pistons that may destroy them in a few short seconds. Nitrous pumps up the torque curve immensely,this is how it adds more power to an engine. It also keeps this added torque to the power peak,increasing hp immensely also.
Nitrous kits are easy to install and service,but they need careful tuning and maintainence in order to work properly and not cause any premature engine problems/failures. You have to pay strict attention to the instructions included in a kit,as some kits differ from others.
Nitrous kits demand fuel pressure under load (engine load) to be a certain psi,usually 5 psi in carb systems,I have no idea what injected systems are run at. Most cars with carbs have a block mounted,or mechanical fuel pump,and FI cars usually have an electric pump in the fuel tank. The FI guys are OK,unless the pump is weak then you must replace it. The guys with carbs will have to buy an electric pump,because even a performance mechanical pump can't pump enough fuel at low engine rpms. You have to mount it as close to the fuel tank as possible,while still being inline with the fuel lines of the car. Mallory,Carter and Holley make excellent pumps for street use.
In order to get fuel to the Nitrous kit,you must tee your line in order to get fuel. FI guys use the Shrader valve on TPIs or LT1s. The carb guys must use a tee cut into the fuel line,which are included in most kits. You then set pressure to the kit at the psi called for in the manual under load,you may or may not need a fuel pressure regulator to do this.
If your motor makes a lot of hp-over 400 by itself,or if you run a lot of nitrous-200 hp or more,it is smart to run two seperate fuel pumps. One should be for the motor and one for the nitrous kit. You may even have to run two 1/2" fuel lines depending on how much hp your motor and kit can produce. If you run into this situation,expect to spend a lot of time and money in order to get enough fuel into your engine.
Nitrous is run from your bottle-usually in the rear of the car,to the front using braided stainless steel AN lines,usually 4AN size. You mount the bottle in your hatch-or trunk and drill a hole through the floor to run the line under the car. You can run the line along the brake lines (I did),or along the fuel lines. You must keep it away from the exhaust,as it will heat the liquid Nitrous into gas-a no-no.
You connect it to the solenoid,and boom your'e done. A good item to add is a filter in line for the nitrous-the kit comes with a screen filter that clogs easily.
Nitrous is easy to hook in electrically to your car,but it must be done neatly and properly. You must connect the power end into a switched terminal in the fuse box-one that is hot only when the key is on. It is a double-safety switch system,one switch is the main power to the system switch,the other is a pushbutton that activates the system only when it is depressed. You have to ground the main switch and solenoids,not the push button-a word of early advice. Also use a decent size wire,as the kit may pull as many as 15 amperes of power-be overly conservative with this. Otherwise it is very simple to hook a kit up,put grommets if you wire through the firewall as a safety measure.
Timing and Nitrous Oxide
Behind fuel,timing is the most important area of Nitrous use to understand and follow. To get maximum power from a naturally aspirated or forced induction motor,you run the timing as high as detonation allows-you get max power there. By using better gas,you can put in more timing and get more power. Nitrous doesn't work that way. You must retard the timing when using Nitrous. Why? Because it pumps up cylinder pressure so much that detonation may occur,resulting usually in broken pistons and bent rods. You definitely don't want to do that!How to set timing:For every 50 hp in Nitrous you add to a motor,you must retard timing by 1-1/2 to 2 degrees in order not to damage parts. For a 150 hp kit,you would take 4-1/2 to 6 degrees of timing out. Since taking timing out when the car is not using Nitrous hurts power,you can either move the timing maually every time,or buy an ignition system that is controlable from inside the car when you want to.
Ignition power and systems
You must, at the minumum have an ignition system that puts out as much power as a stock system. Those cars with better ignition sytems will make more power on and off Nitrous. You can upgrade your ignition in a few ways:wires-buy new high performance wires and put then in.
Plugs- nitrous likes the use of plugs one heat range colder then stock,also gap plugs according to stock or nitrous kit specifications (if there are any);Coil-use a coil with more power;Ignition box-use a quality box with a built in motor rev limiter,it increases spark power to the coil. By doing all of these upgrades,you will greatly increase ignition power and can gain up to 15 hp alone.
What does Nitrous work best with?
Nitrous needs a few things in order to work to its full potential. First,you need a free flow exhaust system-headers,3" cat (f-bodies),and a good 3" cat back exhaust. Second,you need good tires,because Nitrous pumps up torque so much you may burn the tires for blocks.
Some parts that hold back normal motors may actually help nitrous motors go faster. For example,if you have 2.73 gears in your car,it is most probably slower than having 3.73 gears. With nitrous,you will not burn as much rubber with the 2.73s,and may even be able to activate the system sooner in your run-making better ETs with lower mph. Torque converters with high stall speeds on street tires with nitrous are a guarantee that you will either burn rubber,or not be able to activate the system as early.
You will need to have a new high performance clutch put in manual cars,autos need a trans prepped for race conditions because the extra torque will kill clutches and other parts very quickly. You should also have a limited slip rear,because the power will certainly overpower a 'one-legger'.
Nitrous also works best with motors that are stock or mildly modified. Those with more modified motors will not see as great an increase in power as non-modified ones. Nitrous works the same in different size motors,depending on kit size.
Building a Nitrous Motor
Guys who use Nitrous or build Nitrous motors professionally have a motto:
Build a nitrous motor as strong as one that would make the same power on the motor only.
This is how to build a motor for Nitrous that will outperform and outlive motors not built only for Nitrous use. It is expensive,as you need parts that are stronger than anything the factory ever put out. You will need pistons,rods,crankshaft,and block for the bottom end.
Nitrous motors need to be built for strength,not high rpms. Lightweight,"loose" motors will not last under Nitrous-you need strong,tight engines in order for you to thrive. First,take the motor apart,clean it and have it machined by a machine shop that specializes in race engines,rebuilding places don't cut the mustard. Second,since you will be spending almost all of your money on a crank,rods,and pistons,you should get a 400 to replace that 305 or 350. Third,get only premuim parts-pink rods,TRW pistons and GM steel cranks are NOT premuim parts. Get 4340 rods-as long as possible-usually 6". Get a stroker crank made out of premuim steel-since the extra cubes only cost a little bit more. Get good pistons-J&E,Wiseco,Manley...etc matched to rod length and crank stroke. Have it balanced and thrown in with the proper parts. Also it is a good idea to have a splayed four bolt main,since the two bolt caps can be weak-stud it also.
The top end is where the power is,bottom end work is only to increase strength,durability,and cubic inch displacement. You need to have the proper intake,heads,and cam in order to make big power. It is best to closely match the cam and heads first,as there are less choices-and possible mistakes,in intake manifolds.
Cams for Nitrous motors will not make peak power at different rpms than motor only cams,but special considerations must be made. The cam controls valve motion,key to power or lack of it. Since Nitrous goes in as a compact liquid and escapes as a pressurized gas,steps must be taken in cam selection in order not to create backpressure that will cut power. If your heads flow better than 80% intake to exhaust,you can use a single pattern cam. If your heads flow under 80%,the backpressure of a single pattern cam is too much,a dual pattern is needed. A single pattern cam has the same duration and valve lift on both intake and exhaust. Dual pattern cams have more exhaust duration and valve lift than intake,allowing more exhaust gas out. The selection should also consider that heads that flow good at higher lifts should use that advantage,roller cams allow a lot more leway in lift vs duration.
Heads must be matched to the cam closely,a head meant for 7500rpm use will be useless on a 5500rpm motor,it will actually hurt power. For advice on how to pick heads for power,look at the sections on motor work and cam selection at this web site. Heads make more power if the ratio of intake to exhaust flow is 80% or greater,otherwise the cam must be a dual pattern to make the max power.
Intakes are also important. If you have a carb motor,you can either get a dual plane or single plane manifold. Each has its own strengths and weaknesses. Dual plane intakes are meant to pump up bottom end torque offsetting the loss of hp high up. You can buy dual plane intakes for high or low rpm duty,still keeping low rpm torque. Those individuals with engines 350 ci and smaller should use a dual plane in order ro pump up torque. Single plane intakes are menat to pump up high rpm hp without considering the loss of low end torque. If you have a large-383 ci or bigger engine that has too much torque to hook up,a single plane is for you,as it will kill some torque and give you more hp on the top end. Nitrous is not picky with type of intake,but the motor is-do the right thing. TPI cars have less choices and therefore less opportunities to pick the wrong intake. If you have a low revving,or small size motor,a stock or ported stock style TPI intake will work best. If you have a higher revving,or larger ci motor that needs all the torque it can get,buy an Accel Superram intake. The Superram will increase high rpm breathing without hurting low end torque. If you have a very high revving,or a motor with too much low end torque,get a TPIS miniram. The Miniram is the same principle as the single plane intake,and GM's LT1 intake is a clone of this.
Types of kits
There are three major styles of kits: The plate system,the dry manifold system,and the direct port system. Each style has its advantages and disadvantages.
Plate systems are the cheapest,easiest to install,and are the least accurate in Nitrous metering to the cylinders. The 'plate' fits under the carb or between the TB and intake in FI cars. It introduces the Nitrous/Fuel mixture all at that point,but distribution to the cylinders is not equal. The carb cars are better suited,as all intake runners are directly under the carb. Those with TPI or LT1 cars have large differences in how much fuel and nitrous each cylinder gets,as some runners are a foot further back than others. Kits range from 50 to 300 hp.
Most 'dry manifold' kits are aimed toward FI cars-TPI and LT1 especially. Instead of the fuel and Nitrous both being introduced in the same point as the plate system,the fuel is injected using the fuel injectors the motor uses-the Nitrous is still injected in the same manner as the plate systems. This style offers several advantages over the plate system:it is easier to install,fuel is more evenly distributed to each cylinder,and it is less messy to install-no fuel teeing. It also has severl distinct disadvantages:it is more expensive,it attempts to combine engine and Nitrous fuel requirements into one system,it uses a pre-set computer chip to meter fuel under Nitrous-if the chip is out of adjustment with the requirements of the Nitrous may cause heavy engine damage. It does not work well with carb motors because of design. Kits run from 100 to 175 hp.
Direct port systems are the most accurate in fuel and Nitrous metering,are the most expensive,require heavy fabrication/modification,and are not easily hidden. Direct port systems put both a fuel and Nitrous line to each intake runner on an engine. Since each runner is individually tuneable,equality can easily exist between cylinders. To do this,each cylinder needs both a Nitrous and Fuel line run it-8 fuel and 8 Nitrous-all bent and installed precisely. It is obvious you should either take the intake off the car first,or better yet,have a pro do it. The kits also are expensive,starting at $700,not including pro intallation. These kits are the safest and most powerful when using Nitrous Oxide. Kits add from 200 to 500+ extra hp.
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