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Effect of nitrous/fuel mixture on
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This shows the same two curves as
before, but now in different colours, and a third (green) fuel rich curve.
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. Power was still 180bhp
however and set this rich it would be very safe to use on a daily basis with
very little danger of engine damage. If the bottle is cold in winter for
example, a similar thing happens 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 less power would be produced too.
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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 safe on any other day even if not optimal.
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. When stopped pull
out all the plugs, and look carefully at the outside ring - not the electrodes.
It should be a nice tan colour with traces of black or spots of soot on it. No
traces of soot or black means that there is no un-oxidised (excess) fuel present
which means not enough fuel.. Nitrous is like oxygen, if you have too much with
no fuel to 'use it up' it will burn your valves and pistons instead which is not
good! Too much fuel will give less or no power increase or even misfiring but it
will not damage your engine
Guide to mixture setting -
Nitrous / Enrichment fuel ratio.
Run your engine at about 1/3 of maximum allowable rpm in neutral. Hold throttle
very still. Now operate N20 system, and RPM should rise rapidly to close to rpm
redline, and then after a second or so should drop back to around 2/3 max rpm
and sound angry and be misfiring loads! Make sure you try this test
because it almost guarantees success first time! Then see below few lines and
try again!
Too much gas/not enough fuel and it
will just rev sky high and not 'splutter' as it should. The opposite is also
true, in that if too rich, it will rev up initially, and then die back to very
low rpm or even stop. Adjust the size of the nitrous or fuel jet to compensate
and try again until it sounds correct as above.
If you are using gravity feed on a
motorcycle for eg without a pump, then the bit of 4mm 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 fueling for about 40 to 50 bhp extra. So
fit a 40bhp nitrous jet to the nitrous solenoid and away you should go! but do
the above test first!
If using a fuel pump and regulator,
then set the regulator at 3, 5, or 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. Then try the test at the beginning of this
section to check you were right!
A bike on one of my computerised dyno systems (my real
business is building dynamometers!) ready to test - this one actually belongs to
Andy at Quill race exhausts.
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