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Nitrous Oxide Solenoid Valve:
Build your own Nitrous Solenoids from cheap air solenoid valves!
Nitrous Solenoid DIY modifications and why you need them!
There's a lot of serious detail on this long page that's essential if you plant
to build your own systems.
(Serious DIY Build and Modify details a long way down this page!)
First a
very rough schematic so you can see what goes where!

Controlling the fuel and nitrous flow
The on / off control is taken care of electrically, as both
solenoids (the on off valves) will be automatically 'off' unless an
electricity supply is turned on. On a bike this can be the horn or
starter button, or a small micro switch on the throttle so as to
activate only at WOT (wide open throttle) conditions.
An arming switch on the dash, or anywhere accessible is also
required so the system only works when you decide to "arm" it..
Actual power increase
provided depends on the amount of Nitrous Oxide and additional fuel
delivered to the motor, and this will be a fixed constant amount
regardless of engine's rpm.
The amount of Nitrous Oxide delivered
depends on the size of the 'jet' fitted into the Nitrous Solenoids
outlet. This jet is fitted into the back of the 1/4" BSP to 4mm OD
nylon fitting required to connect the 4mm OD blue nylon pipe to the
Solenoid Valve.
The best jets to use are 'Weber'
carburettor jets
available from many places. These are like cheese head screws, with
a 5mm metric thread and a hole down the middle! (So if you can drill
a hole down a screw you can make your own, as I do now. Actually M5
short stainless cap headed (Allen heads) are ideal jets once
drilled. In all cases these jets like Japanese Mikuni jets / Weber
jets, are all marked in Millimetres ID, or bore. So a 125 main
jet on a bike is 1.25mm bore.
These
cheap plastic 1/8th BSP to 4mm nylon tube push and lock fittings are
also available in brass or plated brass and with nuts and olives for
greater security, but these work just fine if you keep your eye on
them!
These screw into the outlets of the two Fuel and Nitrous
solenoids One is shown drilled and tapped to accept the nitrous flow
control jet - Actually its a Weber carburettor main jet from the
local ford dealership...
Now the fun
bit..
Nitrous can give literally as much extra power as you want, with the
limiting factor being only "detonation" or physical strength of
gearbox or whichever bit breaks first!
THIS IS THE ONLY REAL DANGER! TEMPTATION!
Most healthy modern
engines can cope easily with a
25% to 40% increase
without any other changes.
So an average Japanese bike that
makes 120 BHP at the back wheel will
(should!) take a 40BHP increase easily,
(and usually, much,
much more!) Lean mixtures and over
advanced ignitions are what does the damage. So retard the
ignition by a good few degrees to begin with, and make very sure
your nitrous system is
set over rich
to start with. The CORRECT
timing and the one that gives the best power will be more retarded
than stock settings because you have more of everything in the
combustion chamber!
This means effectively higher compression. This also
means that less initial advance will be needed as the oxygen rich,
more densely packed cylinder also burns much faster. The
faster pressure rise means a more retarded ignition will be
needed, to prevent detonation. Also use smaller plug gaps with stock
ignition systems, colder plugs, and higher octane fuel all to
prevent the possibility of detonation. Just in case!
How much power will a given jet give?
Click
HERE
for PDF document
You will need
this chart if you plan to build your own systems...
Buy a cheap small drill set! And a handheld "pin" drill. Now you can
drill ANY jet you might want in a couple of minutes!

Tiny M5 Alloy anodised Allen screws make excellent jets! (If you
cannot buy the Weber ones locally. Remember a "jet" is simply
a screw with a small hole in it, that's all! Nothing technical
here!
Now using my chart you can see that its easy to work out how much
fuel you will need for any given nitrous jet size. But remember that
this is a safe/rich guide only on most non turbo motors. Weather you
get this fuel volume delivered by low pressure by a big fuel jet, or
by using a very small jet and tapping into the fuel rail on a modern
fuel injection car (3 bar) makes no difference!
The fuel flow is
controlled via a similar jet in the same position in the fuel
solenoid. At 10 psi regulated fuel pressure the correct fuel jet is
about the same size as the nitrous jet used - but
every installation is different. Mixture setting : Read this
carefully!
A single injection
point usually gives better distribution, as flow is constant and
each cylinder inducts at different times. No jets are needed at the
injection point only the ones fitted at the solenoids are required.
If more than 1 point of injection is used then a distribution block
or several tee joints will be needed. All pipes going to the
injectors must be the same length.
Inline X2 X3 and X4
plastic push lock fittings are available for the 4mm plastic / nylon
tube and these are ideal, but several tees are
also ok - see pic! All compressed
air/pneumatics dealers keep these kinds of fittings for industry.
Pipework from Solenoid Valves to Engine
Inlet manifold or cylinder head or carb rubbers must be tapped M5 to
allow the fuel and nitrous injection points to be added.
Fittings
with a nut and olive or push lock fittings can be used, available
for industrial airline or hydraulic system use. These fit the ends
of your 4mm OD nylon pipes and have an M5 male thread. The Nitrous
ones must be fitted in such a way as to atomize the fuel and carry
it into the engine. This may require a little thought before you
drill any holes!! It may be possible to use just one nitrous and one
fuel injector for the whole motor or a pair of each, if fuel
injected or turbocharged, depending on layout and throttle bodies
etc. Bikes will normally need to have one Nitrous and one fuel
injector per cylinder, unless turboed.
A single injection
point usually gives better distribution, as flow is constant and
each cylinder inducts at different times. No jets are needed at the
injection point only the ones fitted at the solenoids are required.
If more than 1 point of injection is used then a distribution block
or several tee joints will be needed. All pipes going to the
injectors must be the same length.
Inline X2 X3 and X4
plastic push lock fittings are available for the 4mm plastic / nylon
tube and these are ideal, but several tees are
also ok - see pic! All compressed
air/pneumatics dealers keep these kinds of fittings for industry.
See below...
.
M&H Pneumatics in
Grimsby (Where I live) keep all the pipe, air fittings, solenoids
etc that I use.
Why jet it at the
solenoids outlet instead of the "Foggers" ???
Lots of people
keep asking why it is jetted at the solenoids themselves rather that at the
point of injection (as all US based commercial systems are). HighPower Nitrous
systems
are also jetted at the solenoids as we all understand why this is
far superior. HighPower did this first, well before anyone else did.
Me, I just looked and saw all the advantages!
THE
REASONS? Basically as follows:
Fuel 1st ? Firstly
there is no air or anything in the fuel line before the solenoid. So
it does not atomise at all here - JUST SOLID LIQUID FUEL - the jet
just controls the flow. It does this equally well if at the
point of injection, (Like NOS etc) or at the solenoid's outlet.
If
there is any air in the lines after the fuel solenoid due to the
pulsing from the motor as different cylinders induct at different
times, - (and there will be) - then the fuel cannot reach the motor
until it has pushed all this air through the small fuel jet at the
inlet manifold end (nozzle?) on US style systems. This increases the
time it takes to for it to arrive at the motor. This means it can go
lean for an instant, when you hit the button on US style systems.
This can start destructive detonation off nicely even if you don't
notice the delay. Or it can result in an instant intake backfire as
you hit the Nitrous button off the line, due to the initial weak
mixture.
If
it's jetted at the solenoid's valve outlet instead, then the correct
flow of fuel starts straight away as there is no restrictive jet at
the end of the line that you have to first push all the air through. It
ALWAYS takes the same time to reach the engine. That is its more consistent.
Nitrous 2nd ? If
you are trying to get reliability and consistency then the nitrous
too must be jetted at the solenoid! Here the jet is
controlling fully dense liquid Nitrous Oxide direct from the bottle.
It is still liquid as the solenoid is supplied by a larger pipe than
its rated flow and it is cool, not attached to the hot engine or
going through hot areas... If the metering flow jet is installed
here then you are measuring a known quantity and density of Nitrous. Every
time.
Alternatively if you fit these metering jets near the hot
(especially at the strip in summer!) motor / engine bay then the pipe
work after the solenoid is both long and hot due to the engines
heat, and the hot engine bay area.
This is much worse when sat on
the start line due to zero airflow. Nitrous (no longer sat as
a liquid at the correct pressure to keep it liquid in the bottle) is
in a long pipe hot pipe! So it boils, expands and "foams" as it
travels towards the metering jets on the engine. So you are now
metering what? A liquid? Or Gas? Or a VARIABLE mixture of
both! In reality in unknown and varying proportions depend on
temperatures and length of the pipe work etc.
Eventually (a few secs
with low thermal mass nylon tube) the pipe is cooled so the liquid
now flows all the way to the metering jets at the nozzle, and you get to
meter a much more dense liquid so it runs leaner later on... So it
is far more accurate to meter it at the solenoids outlet where it is
still a liquid. Here the density remains pretty constant at all
times.
Fitting the metering jets at the
"end of the line" will obviously work, as all the US based NOS /
Nitrous Express etc; systems show, but it is simply not as good a
solution. I know I tried it both ways and did lots of testing.
Plus... More importantly still:
If you decide to use a Nitrous controller that pulses the solenoids
to control the power, with the jet fitted directly to the solenoid
the amount of nitrous you get is proportional to the length of the
pulse width. So 50 percent open time will give half the Nitrous
flow..
If the jetting is at the inlet manifold end / port, then the size of
the solenoids seat is the limiting factor - not the jet, as the
pipework becomes a Nitrous "reservoir" that the solenoid just keeps
topping up...
This means that for
example a
solenoid rated at 150bhp maximum flow would flow around 75bhp of
Nitrous at a 50% pulse width. If the jet on the end of this pipe is
a 25bhp jet for e.g., then the solenoid just keeps topping up the
reservoir, (the pipe work) so you would get about 20bhp at a 50
percent setting! This is not too serious unless you consider that
the fuel is not compressible so it will be giving a true 50
percent... Melted pistons anyone??
Another quick description!
This was in reply
to an email question.
Because in the beginning there
was NOS...
Then came a massive multitude of
clone systems designed by someone without a brain!
Trevor Langfield (The Wizard of
NOS or High-power Nitrous Systems) also jets at the
solenoid - he did it first. Here is why...
1) Fuel line gets full of air as
the fuel drains out of the (oversized) line. Now when the
solenoid opens it has to push out the air first, sometimes
taking a full second! During this time you are metering only
air. And because of the often hot (engine bay in summer!) lines
it gets worse! The fuel can boil and vaporise along the hot
line and some jets get fed only fuel vapour for some time! And
the higher the thermal mass of the often metal braided lines the
longer this happens for. So apart from the air being in the
way, the temperature also makes a difference! Sometimes a very
expensive (nitrous only = backfire) one!
2) The fuel line isn't the only
problem! The nitrous line also has problems. Now on a cold day
the liquid nitrous will most likely stay liquid (mostly) all the
way to the jet. Except that it gives off gas (boils) as it goes
from the solenoid into the lines and boils off further as it
goes through distribution blocks etc. Add to this the fact that
the lines are hot in summer under the bonnet, and you can see
that you have no real idea quite how dense (how "liquid") the
foaming nitrous oxide now is! Its density varies between pure
dense liquid, and pure gas. And everything in
between. Remember you are trying to meter the weight of Nitrous
delivered accurately! But are you metering vapour, gas, or a
mixture of the two? Who knows. It depends on Pipe volume, Pipe
thermal mass, pipe temperature. Pipe internal volume. Now to
keep accurate control of the mixture from when you hit the
button. After the nitrous cools the line down (by the very act
of boiling off and reducing density) it will eventually reach
the jet as a say 90 percent dense liquid. All depends on too
many things!
Typically what happens on a cold
day / cold engine bay is this.
Press button LIQUID Nitrous
reaches the engine in say .3 of a sec, because its all cool.
You meter the full 100bhp of nitrous. The fuel though takes up
to a say half sec (or more) to push all the air out of the
oversized lines through the jets before it arrives. So
initially very weak mixture that can start off detonation that
never goes away! Or could cause a weak intake "backfire"...
Hot day/engine bay. Hit
button. Fuel gets there and is flowing properly in 0.5 but the
nitrous takes ages to "get going" because you are only metering
gas or vapour (thousands of times less dense) for anything up to
3 secs! You see this a lot. Recognised by a puff of black
smoke at launch. It just costs performance.
Solenoids - Modifying and Buying Details..
The Solenoid valves that I
use are available from the same type of industrial compressed air /
hydraulic suppliers as the other fittings and nylon tubing. They are
quite common in factories. They have an
inlet at one end and an outlet at the other so are axial rather than
the NOS type. This is neither an advantage or a disadvantage
as I see it.

The
solenoids that I use, are very simple pneumatics
(compressed air) industrial ones. They are available in
different makes, materials and styles but are rated at
only 140psi. This is fine and can be used unmodified for
Petroleum, Methanol etc, but MUST be modified to work at
much higher pressures of Nitrous Oxide. For this reason,
to work with 12V dc automotive systems, a stock 12V is
fine for fuel, but a 6V dc one must be obtained for
Nitrous use. A 12V one will work but only up to around
70bhp extra, where a 6V one will allow a larger seat
area to be used and is completely reliable even on 12V
supply (because cold liquid Nitrous Oxide flows through
it and cools it) so can go up to 140 brake horsepower
extra. A 12V and 6Volt electromagnet is shown here, both
fit the same actual valve body.
These solenoids came from a small
factory unit in Grimsby in the UK called M&H
Pneumatics, call them on +44 (0)1472 241370 and fax on
same codes but 346402. They are not
on the net...
Although these people may be able to help
http://www.kvautomation.co.uk/ even with a ready to
go solution! At a price. But you will need to order
large quantities.
Or maybe here
http://www.aeroconsystems.com/plumbing/solenoids.htm
)
Similar ones are made by many manufacturers around the
world, and have seen a few that could also be easily
modified. Nitrous ready ones can also be bought,
according to a recent email, contents
here.
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The fuel
and the nitrous are both "jetted" to control the amount
of power increase given. The jets are in the form of a
simple carb type jet, in this case a Weber carb jet, and
these are fitted into the rear part of the pipe fitting
that screws into the outlet of the fuel and nitrous
solenoids. All three shown serve the exact same purpose.
All
are drilled and tapped to take a "control jet" and are
standard easily obtained fittings. The all plastic one
is cheapest and cannot corrode, and has low thermal mass
but the brass one is safer as it uses nuts and olives to
hold the nylon pipe rather than simple push/lock
fittings. All accept 4mm nylon tube, and are male 1/8th
BSP thread, to fit the outlets of the solenoid valves.
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This is a
Weber carburettor jet (1mm bore or 100 jet size, so
limits the nitrous flow to 70bhp). The rear of the
plastic fitting is drilled and tapped M5 thread and
countersunk to allow the jet to fit flush. |
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Half
unscrewed... |
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Completely unscrewed! This "jet" can be a brass M5 grub
screw, or M4 Alloy Allen headed set screw, or whatever,
but drilled to form a jet. Small drill sets are much
cheaper than buying bucketfuls of ready made jets!
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The
fitting here is about to be fitted to a standard
solenoid for the enrichment fuel. This is jetted in
exactly the same as the nitrous one. In the outlet. |
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1/8th BSP
1/4 inch "tail" for the petrol pipe goes in the end
inlet end of the fuel solenoid.. |
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The
internal "bore" of a stock solenoid is 1/8th inch, or
3mm - you can see this by looking down the end of the
valve. |
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Here is
the same view of my modified one, with smaller new seat
fitted. |
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Here is a
modified one (similar view of unmodified one 9 pictures
above!) to make it work at up to 1100psi, and with
liquid Nitrous Oxide) It has to have a much smaller seat
area. The old one needs to be drilled out, and a much
more accurate and much smaller one machining up, and
soft soldering in place. The plunger or piston on a
stock one also has to be modified. The stock rubber type
material is fine for fuel, or air, but will not work
with nitrous! Check out the small nylon or PTFE black "Bic
Biro" pen ends! there are two spare ones in the picture.
Compare this to the photograph 9 places above, and also
the new smaller seat area... (The ENLARGED bit!) |
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Another
picture of the new seat. |
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Also
detail of the modified Piston/plunger. The one with a
"blob" sticking out is the modified one. PTFE works just
as well, if no suitable pens can be found! |
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This is
the other end of the piston. The modified one has had to
have about 3mm machined off the end to give the correct
(1.5 times the bore of the new seat) lift. |
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Ready to
fit, tested at 1100psi down to 10 volts, and works
reliably and never leaks. If it will not open, then your
seat area is too large or the area of the "seat rim" is
too wide. The pressure will then hold it closed even
when you apply power. |
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A simple
nitrous injector/or nozzle. It has no jet. That lives at
the solenoid outlet, this simply has to direct the flow
in such a way as it collects and atomises the fuel as
shown in the diagram. The nitrous must atomize the extra
fuel well. The shiny bit is just a bit if brass tube
from a local model shop, with a small 2mm hole drilled
in the side, and the end soldered up. The plastic
fitting has a M5 thread tapped in the bottom, and a 5mm
grub screw screwed into it. This was drilled to accept
the brass tube, and was all soldered together and tinned
to make it silver at the same time.
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Ok, for a
clearer idea here is a fake inlet port or throttle body
I made earlier! See the small hole in the side of the
brass tube? it simply directs the nitrous down the port
towards the engine. The fuel is added in front of it, so
the nitrous collects it and atomises it. These fittings
are a bit big, but I made them just for the photograph,
for clarity. In reality I use various different methods
to achieve the same result, and in any case small M5
fittings. Often two small fittings can be fitted angled
together slightly to achieve the same effect without any
brass tube...
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Pair of
solenoids ready to fit to my V8 Sierra car. This was to
begin with, so only 70 BHP extra. This meant a 1mm
Nitrous Jet fitted into the fitting where the blue pipe
is, and a 1.3mm jet fitted into the outlet of the
fitting where the black pipe goes in the fuel solenoid
valve. This was at 4 to 5psi of fuel pressure that also
feeds the twin SU carburettors. The fuel solenoid was
simply teed into the supply pipe. The nitrous solenoid
obviously connects to the bottle in the back! (In this
case with braided brake pipe.) Both of the 4mm pipes
seen here are teed off (split two ways) to go to each
one of the two carbs. In this installation the carbs
were tapped and drilled in the bottom of each "mounting
flange" so nothing could be seen! The solenoids were
mounted near the cars fuse box and were not
noticeable...
It really IS this simple!
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 A typical example for a bike motor drawn but same
principles apply to any engine! |
*Technically
the term NOS is incorrect as this refers to an specific
company (called Nitrous Oxide Systems, in the US) |