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Deze reply is gepost in de afdeling Main Forum in het onderwerp 'NOS' (ID 8881).
De reply is geschreven door Daan Da Man (UserID 1361) op 21-4-2003 13:30.

Now the fun bit.. Nitrous can give as much extra power as you want, with the limiting factor being detonation or physical strength of gearbox or whichever bit breaks first! THIS IS THE ONLY REAL DANGER! TEMPTATION! (Don't ask me how I know this! - Clue, I am very greedy!)

Most healthy modern engines can cope with a 25 to 40% increase easily. 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 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, prevent unnecessarily high cylinder pressures, and prevent detonation that kills engines! Do not ignore this bit! Also use smaller plug gaps, colder plugs, and higher octane fuel all to prevent the possibility of detonation. Just in case!

Ok Sizes.... How much power will a given jet give?

Well that depends on, engine type and efficiency, bottle temperature and pressure, how over rich your system is amongst other variables.

But generally the following formula applies: (Except with turbos, where the power increase is usually higher than expected!)

Learn this bit! (Formula)

Jet size in Millimeters x itself x 70 = power increase (under ideal conditions.)

So in the case of a 120 Weber carb main jet (or rather any 1.2mm drilling or 1.2mm jet) we get: 1.2 x 1.2 = 1.44 x 70 = 100.8 BHP extra. This formula works for all jet sizes as a general guide because the area of the jet is what matters as long as the pressure remains the same.

But since you are all lazy, I worked a few out for you! Buy a cheap small drill set! 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!)

Nitrous Jet Size
in
Millimeters
Extra
Horsepower
Gain
0.25mm = 4.30 bhp
0.30mm = 6.30 bhp
0.35mm = 8.75 bhp
0.40mm = 11.20 bhp
0.45mm = 14.17 bhp
0.50mm = 17.50 bhp

0.55mm = 21.17 bhp
0.60mm = 25.20 bhp *
0.65mm = 29.57 bhp
0.70mm = 34.30 bhp
0.75mm = 39.37 bhp **
0.80mm = 44.80 bhp ***
0.90mm = 56.00 bhp
1.00mm = 70.00 bhp
1.10mm = 84.70 bhp
1.20mm = 100.8 bhp
1.30mm = 118.00 bhp
1.40mm = 137.20 bhp ****
1.50mm = 157.00 bhp
1.60mm = 179.20 bhp
1.70mm = 202.30 bhp
1.80mm = 226.80 bhp
1.90mm = 252.70 bhp
2.00mm = 280.00 bhp
* A starting point with a 1.50mm fuel jet with gravity feed on bikes!
** Suggested starting point for gravity fed bikes with a 1.9 mm fuel jet.
*** If 4mm o/d nylon pipe is used from solenoid to fuel nozzle with a 2.1 to 2.2mm internal bore (as it normally is) no jet should be needed here at all as the pipe forms the fuel line restriction on a gravity fed system Mixture should be about right. BUT CHECK IT!
Above this level of power increase, gravity supply will not be enough. This works well up to a .8mm nitrous jet, provided that the bikes fuel tank is above the motor (some are not!) If the tank is not above the motor, or more power than this is needed, then a fuel pump of some kind will be needed, as it will with all cars. Fortunately, many modern bikes and all cars already have one. If it has sufficient extra capacity this can be used just by "teeing" into it before the carbs or fuel injection system. If not, or you are unsure best fit an extra one! A lack of fuel is a really bad plan, and it will ruin your day...

**** This needs no jet. This is the (maximum) size of the orifice drilled in the modified solenoids seat. So no jet is needed. You may be modifying different solenoids, or be using larger ones already, so bigger jet sizes are also included. If you want more than 140bhp extra then more than 1 solenoid would be needed if you use the same ones as I did.

With a pumped fuel system, the roughly correct amount of fuel for this hypothetical 1mm 70 brake extra nitrous jet would be around a pint delivered to the engine in 75 to 80 seconds. On a low pump pressure into a normally aspirated motor. So a trip to the pub for a pint glass will be in order... This is only a ROUGH guide!!! A starting point.

So for twice this, say 140bhp, you would start with a pint of fuel delivered in half that time. 40 Secs.

So for 35bhp you would be looking for a pint of fuel delivered in around 160 Secs.

A quick (APPROX!!!) guide for the lazy! Remember that this will be about right for most, but every car/bike and system is different slightly. And the more you add, the richer and more retarded you need to go.

Nitrous Jet Size mm
Estimated HorsePower Increase
A Pint of fuel (Petroleum)
delivered in ?

0.30mm 6.3 bhp 14 min 0 secs
0.40mm 11.2 bhp 8 mins 24 secs
0.50mm 17.5 bhp 5 mins 20 secs
0.60mm 25.2 bhp 3 mins 43 secs
0.80mm 44.8 bhp 2 mins 10 secs
0.90mm 56.7 bhp 1 min 73 secs
1.00mm 70 bhp 1 min 20 secs
1.10mm 84 bhp 1 min 13 secs
1.20mm 100.8 bhp 56 secs
1.30mm 118 bhp 48 secs
1.40mm 137.2 bhp 40 secs

Now 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 (follow link!)

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