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> Important N2Oinformation: Stuff you MUST understand if use any make or build your own Nitrous Kit!

John WilliamsonImportant Information for building Nitrous Systems

This page is heavy going but you really need to know it!

The scary bit of any home built or designed Nitrous System is testing it for the first time! This page is therefore ESSENTIAL reading. Before you do!

To generate more power, you need to add extra fuel, and extra oxygen (or rather Nitrous Oxide in this case, which amounts to the same thing) to burn this additional fuel.


The Nitrous system operates as all nitrous systems do, as follows:

The bottle (tank) which has around 750psi of vapour pressure normally on an average miserable cool day day here in the UK, (depends only on temperature) feeds liquid nitrous oxide (via an upside down bottle or a 'siphon' tube inside of it) to the electronic on/off valve or "Nitrous Solenoid" valve.

This is operated in an on / off fashion to switch the flow of Nitrous Oxide on and off, electrically, via a switch, or micro switch on the throttle. It should only work at full throttle (WOT) condition.

After the Solenoid valve and a flow control jet situated at the exit of the Solenoid valve it enters the inlet manifold via some 4mm Nylon tubing and one or two fittings.. We now have a means of switching a flow of Nitrous Oxide Liquid on and off blasting into the inlet manifold! If you do not understand this section please read it again!

At the same time: Fuel from the existing fuel pump, if big enough, or a new fuel supply pump entirely if you prefer! (or even gravity on some bikes) is fed to a second electronic Solenoid valve.

This is very similar to the one we fitted to control the Nitrous Flow. Only it allows fuel instead, to flow when energised. This is wired to operate when the Nitrous valve opens. Both the Nitrous, and the Fuel solenoid are connected together, electrically. So both fuel and nitrous are switched on and off together!  The fuel also leaves this fuel Solenoid when energised, via a small control jet.  It also flows via some 4mm Nylon pipe into the inlet manifold.  This gives the Nitrous Oxide some fuel to burn!

Inside the manifold, the flow of nitrous is arranged so that it hits the flow of fuel and finely atomises it. The Atomised fuel, and cold semi liquid/gaseous boiling nitrous are carried into the engines cylinders with the normal airflow in the port to the cylinder.

In summary... Since these 2 Solenoids are both wired together, they will always open and close together as one. The pipes are fitted into the engine in such a way that the Nitrous Oxide hits the stream of fuel entering the engine and finely atomizes it into droplets. This is important as you don't want un-atomized liquid fuel flowing through the motor for lots of reasons, the most important of which is that the stuff will not burn as it is in big droplets and gets spat out of the tailpipe! 

The extra power comes from the extra charge in the cylinders, of oxygen and fuel. The extra Oxygen comes from the breakdown of the Nitrous Oxide gas compound, into Nitrogen and Oxygen due to cylinder temperatures.  Additional power and a deal of "anti detonation" comes from  from the powerful charge cooling effect that the liquid Nitrous oxide has on the incoming charge as it turns to a gas from a liquid state. It does this partly inside the inlet tract, as it "boils" from liquid into gas as it emerges from the injection point.

This "point" may be a single point say at the throttle body on fuel injected cars, or directly into the inlet ports on most bikes, but the effect is the same. In all cases the charge is cooled, extra fuel is added, and atomized.

This additional Oxygen and fuel in each intake cycle increases cylinder pressures (and temperatures), and therefore engine torque and power, quite drastically! As we will see below.

First an idea of what is possible...

A friend - Gary Atkinson, added a system that I built for him, for a laugh at the drag strip. He didn't care about his engine at all so we started a bit "high" on the boost levels...  A slightly mental 140bhp extra on a single stage just to begin with, fitted to a standard Suzuki GSXR1100 N motor in a "competition drag bike" chassis (which means long, low, big fat slick etc)

His 1/4 mile times and speeds went from 11.23 secs @ 119mph (expected) to an astonishing 9.10 secs @ 156 mph, with only stronger clutch springs and a 6 degrees retarded ignition from standard engine! threw most of the oil out the breather (into a now much bigger catch can!) on every run. I suspect it needed a little less ignition advance still and this would have cured it - AND made it even faster.

Unfortunately the bike was just too long to fit on my Dyno (Dynamometer) so I have got no ridiculous power curves to show you. It was making a VERY strong 260BHP+ judging by its performance on the drag strip. With ENORMOUS torque levels. It certainly sounded extremely angry!  I don't suggest you go for as much extra power as this on a stock engine, but it just shows just how safe a  a small "40bhp+ dose" extra really is on these particular Suzuki engines. 140 bhp extra from about 3000 revs (where it normally has about 30bhp) is a 450 % boost at these revs! And over 100 percent at 9500rpm...

Gary's bike ran all season like this without any problems. Other than annoying all the other competitors who spent thousands on "conventional engine tuning" in the accepted sense. It simply is not really necessary, other than to fit stronger transmission parts in extreme cases with really big power  increases. And on some engines maybe some stronger "forged" type pistons.

OK... now a more "normal" sensible 50bhp increase on a completely stock bike engine (Mine).

Below is a normal power curve(s) with, and without N20 from my own otherwise completely standard road going Suzuki GSXR1100 WP (Factory power restriction "plates" removed) with its stock, quiet exhaust system and everything. Bottle was hidden. This will give you an idea of how much of a 'hit' that it's relatively small l 50 bhp extra really gives you!  It's plenty...

The BLUE line is with the N20, GREEN line without, all at 400 miles old!!! (I never had any mechanical sympathy!) The Nitrous button was pushed as the revs hit 7400 rpm on this particular dyno run. Power is up from 137 BHP standard figure, up to 190 BHP at the rear wheel for the price a few beers!  Now that's cheap performance. This engine had never even had a spark plug out so far. It was brand new! (Obviously, an open free flowing exhaust, and cooler plugs would see it well over 200BHP mark as the stock exhaust system is obviously restrictive at 190BHP. Remember this was stock timing, stock EVERYTHING!

The "perfect" fuel mixture setup is slightly rich for engine safety reasons, and as can be seen on graph, it is set up a little richer than optimum on purpose. There is more to be had even with this nitrous jet by leaning the mixture off a touch. But why try, when the last few BHP mean huge temperature rises, and greater peak pressures and possible detonation problems.

Look at the curves. The nitrous gets to the engine faster than the fuel does so if set up a touch rich the power rises as can be seen on the initial hit at 7400 rpm and then settles back a fraction as the fuel flow arrives and stabilises and the curve is then a little uneven, instead of exactly the same shape as the stock curve but simply higher up the page as it should be with a smaller fuel jet. This shows me its a fraction rich without even plugging the Gas analyser in. This is how it SHOULD be on a safe set up road bike.

I did actually try a smaller fuel jet just out of interest and the bike made only 5bhp more, without a safety cushion of the excess fuel. Simply not worth the risk. Click the graph to see what happened with a much bigger fuel jet making it richer still. All of this was with stock ignition timing and exhaust system etc, in fact it was not even run in although it probably is by now!

Click here or on this graph to see another graph of rich mixture e
and to find out how to set up Nitrous / Fuel mixture ratio!

Click to see a richer run as well as these two

The torque curves below, (same GSXR1100WP with and without Nitrous operated) show the rather drastic "sudden go" effect much more clearly!  Whilst this looks good on the graph its extremely sudden on the road... You may want to start with 25BHP extra! (Sudden means it feels like someone just hit your bike up the back with a Cricket Bat) You get longer arms and the front wheel comes up even in 3rd gear by mistake.

Torque is directly comparable to acceleration, it is actually a measure of acceleration "directly" or "actual thrust at the back wheel" on the dynamometers roller, so this is exactly what you would actually 'feel' through your backside as you hit that button. Remember this is only a relatively small shot on a stock quiet standard bike! This does not compare to what my old 1100 EFE Suzuki had (GS1100 if you are an American). That had two stages of Nitrous so you got one on the throttle, and the second one on a button! That one was very lively!


Torque is up by 50+ percent at the push of a button - at the rpm that the vertical blue line shows 7798rpm, which on the road is all rather sudden! The front end comes up very fast in most gears, which I just love! (I am power crazed OK?)

If the button is pushed at a lower rpm, engine damage is more likely (or at least possible) due to the enormous torque that would be produced as the Nitrous Oxide tries to make its + 50BHP extra completely regardless of the engines revs!  Great if you fancy driving over the crankshaft... Notice that the torque increase, which is directly proportional to the pressure in the cylinders, is greater at lower revs, just look at the graph, and try to mentally draw the line back in your mind. Imagine how high the torque increase would be at say 4000 rpm!

The Reason

Imagine a string chopping machine -- the "string" (your Nitrous & fuel mix) goes in at constant rate or speed because it is regulated only by a fixed jet, and constant pressure. Like a hose pipe!  The Nitrous Flow and extra fuel flow is CONSTANT, and not RPM dependent. 

If the string chopper (your engine) is going at high speed it chops off lots of little bits. (so your engine is safe - small bites!)

 If your string chopper slows down it takes bigger bites at a time! So the torque increase and cylinder pressure climb as the revs are reduced. If its turning really slowly, its like setting a bomb off in the cylinder! Because its got a HUGE dose of Nitrous/Fuel in there...

If you relate this to a bike or car engine taking a huge dose of Nitrous and Fuel (because the revs are too low) then the cylinder pressures are enormous. This means greater torque increases as rpm's drop. See torque graph. Or if its easier Nitrous has much more drastic effects and MORE effect at lower RPM's. So it makes cars ACCELERATE much harder! And you do not need much...

Its also the reason why you don't want to hit the Nitrous button at low rpm in top gear... This would be OK in low gears (like off the line at the drag strip) as the revs jump up sky high, tyre lets go a little and you bugger off at high speed, so no problem - But in top in town it can't do this, so you could damage your engine if you try it? Depends on the Amount...

Try and draw an imaginary nitrous line on the torque graph back to say 2000 rpm and you will get the idea!

Anyone wanting a copy of this (My own) Dyno Software with these and other runs included can get it from here, because I build dyno systems as well!  Or rather I provide the software and electronics and you build the rest.. Get software

Mixture Settings

Effect of nitrous/fuel mixture on power
This Dyno print out shows the same two curves as before, but now in different colours, and with a third additional dyno run added - green line... This was the Fuel rich  curve, caused by going up a size in the Nitrous systems Fuel jet.

1. The blue power curve shows the stock bike without the nitrous system in operation.

2. The red curve shows the same bike with the nitrous system set up with the correct or very slightly rich nitrous and fuel ratio. The extra 'richness' prevents detonation, and danger of burning the motor internals.

3. The green curve shows the same bike with the nitrous system set up fuel rich, to show the effect on the power curve, The system was operated earlier this time during the run at 6400rpm, and the richer mixture lowers the peak power produced, and gives a 'wiggly' looking curve. It ran cleanly as far as you could tell however with no misfires or anything. Power was still 180bhp peak and set up this rich it would be very safe to use on a daily basis on the road with no danger ever of any engine damage. If the bottle is cold in winter for example, a similar thing happens anyway as the pressure is lower in the bottle, but this time the rich mixture is caused by less Nitrous, rather than too much fuel so even less power would be produced too.

Click graph to enlarge!

Ideally you would set the Nitrous system up to be like the red curve (just a little too rich) on a hot day so that it will be very safe on any other day even if not completely optimal. At least if you care about your engine.

A full throttle 'plug chop' on Nitrous, will also give a good idea if you have the mixture correct, if no dynamometer is available. Just run flat out through 3rd, 4th, 5th gear and then release the Nitrous button hit the 'kill' switch and disengage the clutch and coast or brake to a halt without letting the motor turn over. Simultaneously...

When stopped pull out all the plugs, and look carefully at the outside ring first - not the electrodes. It should be a nice dark tan colour with some slight traces of black or spots of soot on it. No traces of soot or black means that there is no un-oxidized (excess) fuel present which means not enough fuel for "safety". 

Nitrous is like oxygen, if you have too much of it with no fuel to burn, it will burn your valves and pistons instead which is not good!  Too much fuel will give less or even no power increase or even misfiring but it will not damage your engine. The correct amount is somewhere in between!



Rough Guide to mixture setting - Nitrous / Enrichment fuel ratio - WITHOUT a handy Dyno and before you try a plug chop!

I suggest you try this only with systems jetted at the solenoids not with US style Systems, because they are a bit unpredictable to put it mildly...

OK... Make sure you have both fuel, and Nitrous firing out of the solenoids, or from the pipes that feed the injector's (Disconnect first to test for flow!)

DO NOT allow any Nitrous/fuel to be fired into a stopped engine ever!
The stuff sits there just waiting for something to ignite it inside the intake system.
When you switch on, or when you crank the engine it will explode! This often just makes a huge and scary bang, but it CAN wreck your intake system, and cause fire or injury.

If you even suspect a solenoid has been fired by mistake, or has leaked into your engine, then you MUST remove the HT coil lead, or disconnect the power to your ignition system and then turn the engine over on the starter to clear it out! Now reconnect and start normally.

Now the scary bit...

Run your engine at about 1/3 of maximum allowable RPM's in neutral. (Example 9000 redline? Test at 3000 RPM's...) Hold throttle very still and do not move it...

Now operate N20 system, and the engines RPM's should rise rapidly, and then after a second or so should drop back to around 2/3 max rpm (say 5 to 7 thousand RPM in this case, and sound a little uneven and a bit spluttery at the exhaust. It may be misfiring and coughing a bit!  But obviously rich with traces of black smoke maybe visible at the exhaust. If it does exactly this then you can go and try it out now on the road/track!

If the revs rise then fall back and it runs too slow and/or it stops completely, it's far too rich!
If the revs rise sky high and stay there! It's too lean, Add fuel! (Bigger fuel jet) Don't go try it out...

If however it sounds metallic, harsh, or strange, stop! and send me an email!
If it sounds like "big end" or "cranky" (ask an older mechanic!) then it may be in need of a few degrees of retard on the ignition. Or could be a bit lean for some reason. Or both.

Make sure you try this test because it almost guarantees success first time! Then see below few lines and try again! 

If you are using gravity feed on a motorcycle for e.g. without a fuel pump, then the bit of 4mm O/D tubing from the solenoid to the engine/distribution block effectively is your fuel jet. Non need be fitted at the fuel solenoid valve. This will provide the correct fuelling for about 40 to 50 bhp extra. So fit a 40bhp nitrous jet to the nitrous solenoid and away you should go! but also do the above test first!

If using a fuel pump and regulator, then set the regulator at 3, to 10 psi as required. At 10 psi the correct fuel jet will be approx the same size as the nitrous jet used, whatever size this is.. At 5 psi you would need a jet about 1.3x bigger. At 3 psi try a jet about 1.5 times bigger to begin with. Or look at my jetting CHART!! Then try the test at the beginning of this section to check you were right!

Superclean dynoroom at Quill-RacingOff Topic... My real business was building automotive dynamometers!
Here is one ready to test...

I started building them to investigate Nitrous Systems initially as there was only really the Dynojet Dyno available for bikes in those days.

Problem was that the DynoJet Dynamometer was a bit clunky software wise and its drum was (and still is) too light. So as usual I built my own better one.. Same with everything I do. But the development cost was a bit high so I started selling them...

This one actually belongs to Andy at Quill Race Exhausts and was one of my first customers for dynamometer systems many many years ago. About 1994 or earlier. Love the floor!


*Technically the term NOS is incorrect as this refers to an specific company (called Nitrous Oxide Systems, in the US)


Web design & contents, Nitrous / fuel Jet Sizing, technical information, pictures, charts are all 1987 and on. Any theft will be pursued vigorously..



















































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