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Nitrous Oxide Rover K-series / General Install

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Nitrous Oxide on a K Series Motor.  


Before getting into the ins and outs of a Nitrous Install and what you need to do to ensure reliability (let alone dispelling the myth that 'Nitrous blows up motors') it is worth defining what Nitrous Oxide is, how it works, what the ramifications are for your motor, how much extra power and torque you can reliably achieve, and what it will cost.


Nitrous is chemically N2O; it boils at minus 54 degrees C where it phase changes from liquid to gas. If kept in a pressurised container, then the Vapour Pressure will keep the Nitrous in liquid form at up to 36 degrees C - at this point the Vapour Pressure (1069psi) can no longer keep nitrous in liquid form and it starts to phase change. So, for all intents and purposes, at normal operating temperatures, Nitrous acts like a refrigerant in that it is always wanting to phase change. Anything that causes drop in local pressure within a Nitrous system (such as poor solenoid flow design, joints in braided line, poor bottle valve design, poor injector design and inefficient jets) will exacerbate phase change.


Note: for maximum efficiency we want to inject liquid nitrous (because of density) so we need a system that will keep phase change to a minimum up to the point of the injector.


More importantly, Nitrous breaks down into Nitrogen and Oxygen at 296 degrees C. Furthermore, Nitrous is, by weight, 36% Oxygen whereas air is only 23.6% Oxygen. Thus, by injecting Nitrous into a motor you can effectively burn a bigger fuel charge per cycle and, hence, produce more Torque; the stoichiometric ratio being 9.649:1 Nitrous to petrol.


In fact, whenever Nitrous is used you inject slightly more petrol so as to ensure the fuel/air mix doesn't run lean, since this would tend to induce detonation, which would (rapidly) destroy the motor - the extra petrol helps to slow the flame front and also acts as a heat sink to carry away the extra combustion heat caused by the bigger fuel/air charge.


There are 2 ways to achieve this extra over-fuelling:


A 'Wet System', such as I use, whereby the fuel or engine management settings on the vehicle don't have to be altered. Wet Nitrous systems being systems that inject metered amounts of Nitrous oxide and fuel at the same time through a common injector.


A 'Dry System', whereby Nitrous is injected through its own injector and the vehicle's ECU is signalled to cause it to over-fuel when the Nitrous is activated. This is probably the future of 'high end' Nitrous systems but is technically far harder to do (for various reasons it's how diesel engines are run on Nitrous).


Therefore I shall only be discussing a Wet System with respect to the K Series motor.


The other benefits of Nitrous (albeit small, and generally only with smaller shots) are that the phase change at the injector cools the fuel/air charge (owing to the effect of Latent Heat of Vaporisation) leading to a denser inlet charge. Additionally, the Nitrogen produced by the breakdown of Nitrous acts as heat sink to carry the extra combustion heat past the exhaust valve.


The major problem with running a Nitrous motor is the fact that the fuel/air charge burns faster (and hotter because there is more fuel being burned), and therefore requires less ignition advance. Indeed, too much ignition advance on a Nitrous motor (especially on larger shots) will result in the very rapid onset of detonation and a lunched engine. I re-iterate, Nitrous and Detonation are not good bedfellows!


It is detonation and/or pre-ignition that has resulted in the myth that Nitrous is dangerous and destroys motors. It doesn't, what destroys Nitrous motors is poor design and inappropriate use. keep a Nitrous motor out of detonation or pre-ignition, don't get too greedy with the amount of Nitrous you use and a Nitrous motor will last just as long as a NAsp motor.


Thus, the amount of Nitrous you can use in any given motor is dictated by piston strength, ignition advance, compression ratio, and fuel octane. That said, more Nitrous can be used on a progressive delivery system than in a single fixed hit.


Bearing the foregoing in mind, just how much Nitrous can be used in a K Series motor?


The ZR 160, TF160 and F Trophy engines have the strongest pistons and can handle more than their brethren (albeit they have slightly weaker con-rods than the earlier engines). I would suggest that no more than a 25bhp shot can be used safely in a fixed hit (I used a fixed 25bhp shot on the Drag Strip in 2006 with no problems). A 50bhp shot can be used but only along with using a Progressive Controller to control the rate of injection (I'd suggest a 50% start level with a 2 second build time). I wouldn't advise using more than a 50bhp shot (and then really only on the ZR160, TF160 or F Trophy engines because of piston strength; with the other models stick to a 25bhp shot) unless you swap out the pistons for forged replacements (and at the same time I'd suggest you fit an uprated multi-shim head gasket). I have trialled a 75bhp shot but there were some issues that needed to be addressed and I haven't yet got around to trying it again.


Note, in terms of the quoted the size of any given shot, this is an (close) estimate since it will depend on the efficiency of how any given motor will utilise Nitrous. For example, on a 50bhp shot my TF produces an extra 55bhp at the wheels (and, more importantly, an extra 75 ft-lbs torque).



So what do we actually need in terms of equipment in order to run a Nitrous injection system?



Simplistically this breaks down into 6 areas:


1. A storage system for the Nitrous, ie a pressure bottle.


2. A means of controlling how the Nitrous and fuel are injected, ie some sort of controllable 'valve' for both the Nitrous and the petrol. Current thinking is to use solenoids to control both the Nitrous and the fuel since this allows a simple 'ON - OFF'system (for fixed hit delivery) or a pulsed 'ON - OFF' system for progressive delivery (qv later). A 'rotary valve' system, known as the 'REVO' is currently being developed by the British company 'Wizards of Nos' (WON) which will be far more efficient (and reliable) than any solenoid based system but it is yet to be released for general use.


3. A means of metering the quantities of Nitrous and fuel to be injected, ie metering jets.


4. A means of mixing the Nitrous and petrol in the inlet manifold (or plenum) to ensure good distribution, ie an injector (or 'fogger').


5. A means of getting the Nitrous and fuel to the injector in such a way that 'phase change' is kept to a minimum until the point of injection, ie pipework.


6. A means of activating / deactivating the Nitrous system.


7. Some means of maintaining bottle pressure. In any Nitrous bottle at any given pressure there is an equilibrium between the %age of Nitrous in liquid form and the %age in gaseous form (because of vapour pressure). As liquid Nitrous flows from the bottle, in order to maintain this equilibrium some of the bottle contents phase change. This results in a drop in bottle temperature (Boyle's Law: Pressure x Volume / Temperature = Constant), leading to a drop in bottle pressure. This effect is exacerbated especially with bigger shots or with longer periods of Nitrous usage. In order to counteract this effect we have an electric heater  'blanket' connected to a bottle pressure sensor, which cycles to keep the bottle at a constant temperature, and therefore, pressure.



So, schematically:




Now, obviously that is a basic schematic and the details will vary dependant upon whether you are using Fuel Injection with a plenum (in which case you will use a single injector upstream of the throttle body), Fuel Injection with Multiple Throttle Bodies (in which case you'd go Direct Port [DP], ie a distribution block and an injector per inlet runner; or a Nitrous and Fuel solenoid plus an injector per runner), or Carburettors (in which case you might use a 'spray plate' down stream of the carb, or a DP set up per runner). Additionally the kit will vary between FI and Carbs (mainly the metering jets) owing to the different fuel pressures involved.


OK so that's the basics, now we need to address just how we control the Nitrous and Fuel flows. Currently this is done using solenoids. We can use a 'fixed hit' for smaller shots of Nitrous, ie the solenoids open, and remain open, until such time as you wish to stop using the system, when they close. The problem with a 'fixed hit' is that it is unkind to the motor and drivetrain because of the shock it causes, additionally it can cause the tyres to break traction suddenly. Thus the size of the shot that can be used on any given motor is limited - 25bhp on a K Series is my maximum recommendation.


To use larger shots of Nitrous we need a system whereby we can control the initial charge delivery size and the rate of increase in delivery. To do this we use a 'Progressive Controller' that is a box of 'electrickery' that can control the solenoids and cause them to pulse at a pre-determined rate so as to control the delivery. Typically such controllers allow you to set the initial %age shot size, final %age shot size, as well as the build time of the shot. So, for example, you might set the controller to 50% initial delivery rising to 100% over a build time of 2 seconds. This gives you a much smoother hit and allows the use of more Nitrous. One should be wary, however, of assuming that it is this simplistic. For example you might think you could fit, say, 100bhp jetting, but set the controller up such that the 'end power' is 50% and assume that you will get a 50bhp shot. This is, in fact, not the case! Because we are using pulsed solenoids (which are effectively merely ON-OFF 'switches') what actually happens in this case is that the motor receives very short 100bhp shots over a shorter time.


So how do we activate/deactivate the system?


Basically we have an 'Arming Circuit', in order to make the system live, and a trigger. The arming circuit should be wired through a gated switch via the Ignition II part of the Ignition circuit since this will ensure that the Nitrous can only flow when the motor is running. Injecting Nitrous into a non running motor is a very bad idea since, owing to the fact that the Inlet and Exhaust valves are not cycling, you have no way of knowing just how much Nitrous has built up in each cylinder (and it will be too much, believe me!). If you now start the engine you will get an almighty 'Nitrous burp' (backfire) which, at the very least will probably blow your entire inlet manifold off (trust me, I've seen it happen!), and at the worst totally lunch your motor.


With regards to the way you trigger the system most (non-Nitrous users) seem to believe you do it with a push button as seen in films like 'The Fast and the Furious' or 'Gone in Sixty Seconds'.


Ladies and Gentlemen, Hollywood knows about the square root of bu**er all about how Nitrous systems work! You cannot learn from such fictions!


To understand why I say this we have to think about why we would use Nitrous and when we would use Nitrous. Nitrous is a 'Power Adder', actually it primarily generates torque, which is used for acceleration.


Therefore you use Nitrous whenever you want to accelerate at the maximum rate. In fact, Nitrous is most efficient at lower rpm because the valves are open longer per unit of time, so you get better cylinder filling (so you tend to 'short shift' compared to NAsp motors). Thus, we want the Nitrous to flow at 'Wide Open Throttle' (WOT). Yes you can use Nitrous to improve the vehicle's top speed (in certain cases) by being able to pull maximum rpm in top gear, but that occurs at WOT anyway! For example, my TF will only normally pull a maximum of 137mph, but will achieve maximum rpm on Nitrous, equating to 155mph.


Now, given that injecting Nitrous into an engine at too low an rpm in too high a gear is a bad idea since it is likely to induce detonation; and given that injecting nitrous into an engine that is 'off load' (such as during a gear shift) is a bad idea as it will cause the engine to over rev; if we think about it, we can see several potential problems using a button to trigger the Nitrous:


If the button is 'non latching' then we need to hold it down in order to use the system. This could cause problems with steering the car if the button is not on the steering wheel. If the button is on the steering wheel and we have a momentary 'aberration' and forget to release the button as we shift gear, then we will over rev the motor = BANG!


If the button is 'latching' then we have to remember to switch off the system every time we shift gear and then switch it back on. Aside from being a PITA, this puts us in the potential situation of making a 'switch pigs' = BANG!


A much simpler (and safer) system is to use a Throttle Position Switch (TPS). This could be an after-market TPS, a TPS fitted by the car manufacturer as standard (eg Fuel Injected vehicles), or something as simple as a microswitch fitted such that it picks up on the throttle cam.


This way, in order to use the system (assuming that you have opened the bottle valve and armed the system!) is merely to bury your right foot - no thinking is needed!





With regards as to which kit to use, well, we need one that is purpose designed to be:


1. Reliable.

2. Hit smoothly so as to minimise risk to the engine and driveline.

3. Efficient, ie maintain the Nitrous in liquid form right up to the point of injection.


IMHO the only kits that do this are those produced by WON.




Yes they are somewhat more expensive (especially given the current US/UK exchange rate) but they are the only kits that are lifetime guaranteed. Furthermore WON give 100% customer support.


Why do I say this?


Well (at the risk of upsetting our American cousins) it's a bit of a 'No Brainer' really. If you take a look at any US system, Holley-NOS, NX, Nytrex, etc, they all use generic solenoids that are not specifically designed for Nitrous. This means that they do not flow particularly well and exacerbate phase change, which leads to inefficiency and the requirement to use more Nitrous in order to get a given level of power increase. More worryingly, these solenoids are not lifetime guaranteed, in fact they require a scheduled rebuild every 'x' amount of times they have been used. More worrying still is the fact that the manufacturers advise the fitting of a back up solenoid - in other words they expect the solenoid to fail! This is a potential disaster area; consider what would happen if you were running on Nitrous and the fuel solenoid failed shut - you would get instant lean out leading to detonation, and a blown motor before you even had time to react to the situation.


WON solenoids (known as 'Pulsoids') are specifically designed for Nitrous use. Furthermore they are lifetime guaranteed and never fail.


US systems use metal braided 'aeroquip' type hose. While this may look 'Gucci' (ooooh, shiny things!), and while it is said to be abrasion resistant (it isn't), this causes 2 problems: Firstly, metal braided hose absorbs heat. Secondly, metal braided hose is not of constant bore - you get 'step' at the point the hose enters any olive. Both these factors exacerbate phase change, which, again, leads to inefficiency and the requirement to use more Nitrous in order to get a given level of power increase. As a result, US kits require an extra 'Purge' solenoid in order to purge the system of gaseous Nitrous. While venting gaseous Nitrous may look all 'cool' and 'boy racerish' it is a waste of Nitrous and therefore a waste of money!


WON hoses are made from a specially designed high-pressure nylon pipe and don't suffer from these effects. WON systems are thus more efficient and don't need purging.


US systems place the Nitrous and fuel metering jets in the injector (fogger). This means that you get a build up (or 'reservoir') of Nitrous and fuel in the lines upstream of the injector. Because these are at different pressures, 900psi Nitrous 30psi fuel (less on carburettor engines), this mean that, as you activate the system, the Nitrous gets through the injector faster than the fuel and you get initial 'lean out'. As a result, US systems hit hard.


WON systems place the metering jet in the base of the Pulsoid, as a result no reservoir builds up and the system hits in a far softer way and delivers the torque in a far more progressive manner.


US systems utilise particularly poor fogger designs that do not ensure good flow distribution and mixing of the Nitrous and fuel. Again this leads to a system that hits harder but, more worryingly, can have major effects on the distribution to each cylinder with potentially catastrophic results.


The WON 'Crossfire' injector is specifically designed to ensure even flow distribution.


US bottles have a 'rupture disc', which blows out if the bottle over-pressurises (leading to the loss of the total bottle contents). Aside from the danger from such a disc, these bottles do not meet European safety standards. They are not 'E' marked and many refill stations will not service them.


WON bottles are 'E' marked and have a 'Safety Pressure Reducing Valve' instead of a rupture disc. Therefore, if the bottle over-pressurises, there is a gradual loss of contents until the safe working pressure (950psi) is reached.



So, as I said, a 'No Brainer', WON systems are lifetime guaranteed, more efficient and hit softer. WON give 100% Customer Support (unlike any other Nitrous company). Furthermore WON will design the system around your motor's needs.




On my TF the kit I use is the Streetblaster 150i, which is a single injector system for a fuel injected car (because I am still using a plenum). This kit comes initially jetted for a 25bhp shot. In terms of Progressive Controllers, I initially used the 'Minimax' (which is a basic controller and perfect for a street car). The total cost of this set up (for a 25bhp increase) was around £930. To move up to a 50bhp shot was merely a matter of changing the metering jets (about £15 a pair).


So I've increased my K Series' power by 55bhp and 75 ft-lbs torque (at the wheels) for less than £1000!


I should point out that I now run a more advanced controller (the 'Max Extreme Race') since it allows me far more functionality both on the Drag Strip and on Track Days. Specifically: it can control my bottle heater, it is tied in to the crank sensor so that I can set minimum and maximum rpms for Nitrous use, it can be tied to my ECU such that the ECU changes ignition maps (ie retards) whenever the Nitrous flows, it has 5 user definable 'power steps' that can be set for each gear, it can monitor both fuel and Nitrous pressure (and kill the system if these parameters go outside defined limits), eventually it can be tied into my rear wheel ABS sensors to cut back the Nitrous if wheel spin occurs.



Some pictures of my install:


Fuel take off



11lb Nitrous Bottle




Pulsoids. Blue = Nitrous, Red = Fuel.




Crossfire Injector




Progressive Controller






Arming Switch




Full Set Up




Note: These photo's were taken with the Minimax controller and before I swapped ECU's.




With regards to any install, you need to keep the Nitrous and fuel feed lines from the solenoids to the injector as short as possible (to prevent heat soak inducing phase change). Furthermore I would suggest that you make the Nitrous line about an inch longer than the fuel line (unless you have a Nitrous Controller that can build in a small delay in Nitrous delivery), the reason being that the Nitrous injects at 900psi while the fuel (in my case) is at around 30psi so the nitrous will get to the injector faster than the fuel. This could cause initial lean out and the extra length in the line helps counteract this effect. The injector needs to be about 2 inches upstream of the throttle body for best flow distribution into the plenum.


If we remember what I said earlier about the fact that it is detonation and/or pre-ignition that kills Nitrous motors then there are a number of things we can do to ensure reliability:


On an engine with a distributor we can retard the ignition to prevent detonation (about 2 degrees per 50bhp shot), however on a standard K Series the MEMS ECU doesn't give us this facility. Those with aftermarket ECU's like me (DTA S60) can have a dedicated 'Nitrous Map' - those with Megasquirt / Megajolt systems would probably need to re-program. Therefore when running on Nitrous, if we can't retard the ignition, we need to use higher octane fuel (since it is more detonation resistant) - this means we are running effectively retarded with respect to the fuel octane with ignition maps set up for 95 RON.


So, if running a 25bhp shot (on a stock TF) you must use a minimum of 97 RON fuel, if running a 50bhp shot use 99 RON (Tesco 99 or Shell V Power).


Another thing you can do to protect your motor is to run cooler grade spark plugs. These are harder and deal better with the increased combustion chamber temperatures when running on Nitrous, ie they help to prevent pre-ignition by not getting so much 'heat soak'. For a 25bhp shot use NGK BKR 7EIX, for a 50bhp shot use NGK BKR 8EIX (the standard plugs NGK PFR 6N-11 [or equivalent] should not be used with Nitrous since they will end up glowing and cause pre-ignition. They will also probably melt!).


Finally, if you are using Nitrous, stay off the rev limiter! Rev limiters work by cutting back the spark - if this happens on Nitrous then the fuel/air charge won't be fully burnt and you will get an excessive build up of Nitrous in the cylinder - when the rev limiter cuts out and the spark returns you will get too lean a mixture leading to detonation  and one almighty 'Nitrous Burp' that is liable to destroy your motor.

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You forgot ONE very important element.


WHERE do you buy your laughing gas, and how much does it cost today.


Last time I filled up it was £35 a charge, but I suspect it must be about 50 now.


That's about 4mins of fun.

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I will make some attempts to repair this thread some time.


It seems Debs, in some bitter, pathetic effort to get the last word has removed the images from her photobucket site...


All a bit pathetic if you ask me.


Any further technical articles will require images uploaded onto my server.

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