BLENDING NlTROMETHANE
BLENDING various proportions of fuels to provide our "experimental"
batches of Nitro laced fuels means that at some time or other we will be left
with quantities of unused fuel of a known percentage mixture strength. Because
of its high cost, leftover fuel is remixed with more fuel to provide a new
batch of greater or lesser Nitro strength as required. To accomplish this,
a special mixing chart below indicates how this can easily be done.
NITRO PERCENTAGE
Provided you know the exact mixture you have in use and the amount, it is
possible to get your supplier to provide additional fuel to bring the total
quantity up to the new required percentage mixture.
On the other hand you can do this yourself by using a hydrometer which is
available specially calibrated for just this use, indicating by percentage
the amount of Nitromethane in the fuel, checked by volume and not weight.
For those unfamiliar with the hydrometer, it is a simple device which uses
a calibrated weight to float in the fluid to be checked, the level at which
the float sits in the fuel indicating the specific gravity of the fuel. As
we know water is 1, Methanol coming out at 0.79 and Nitromethane at 1.13,
it is easy to establish the fuel mixture.
To avoid having to consult tables or graphs the special hydrometer mentioned
is directly calibrated, so you just read off the actual content of Nitromethane
in percent.
FUEL TEMPERATURE
It must be mentioned here that the average fuel test hydrometer is calibrated
to give a completely accurate reading at one specific temperature, usually
68 degrees Fahrenheit. Thus if you check 100 percent Nitromethane solution
which is at 68 degrees Fahrenheit, the hydrometer will give you a reading
of 100.
If you mix one gallon each of 100 percent nitro and methanol and the temperature
of this solution remains at 68 degrees your reading will be 50 on the hydrometer
scale indicating that you have a 50-50 mix or 50 percent nitro content. Mix
any ratio of nitro and methanol with the temperature at 68° F and the
hydrometer will accurately indicate the percentage, be it 10 percent, 40 percent,
80 percent or any other ratio.
EXAMPLE: Our tank contains a 55% nitromethane mix and we wish to reduce it to 20% by the addition of straight methanol. On the graph draw a connecting line between the two percentages to be mixed with the lowest percentage (in this case 0%) on the left. Where this line intersects the required percentage line (20%), draw another vertically down to the base line. The number of pints to the left of this line (in this case just under 3) is the amount of the high percentage (55% in our example) required, and the number of pints to the right of the line is the amount of the lowest percentage (0% or straight methanol in our case) required. The two amounts will total one gallon.
Changes away from the baseline temperature of the fuel (68° F) will have
an effect on the hydrometer reading. Changes in fuel temperature affect the
specific gravity of the nitro and therefore give you a false reading.
If the temperature drops the reading will be high, giving the impression that
the nitro content of the mix is higher than it really is. If the temperature
goes up the reading will drop, causing you to assume that there is less nitro
in the mixture than there really is.
Here lies. the danger - the natural mistake in this instance would be to compensate
for the false reading by adding more nitro, with the possibility that your
engine may run lean with damaging results.
If you run strictly according to volume (for example mix three gallons of
nitro to one of methanol for a 75 percent mix) you'll always be on the safe
side. However, unless you want to keep running that same mix, you will either
have to dump what is left in the tank when you want to change percentage or
use a hydrometer.
With the hydrometer however, you can run into trouble, as you will NEVER find
a location where you can guarantee the ambient temperature will be 68°F,
and you will need to measure the temperature of the fuel before attempting
to determine the percentage of nitro it contains.
Whatever the true percentage of nitro in your tank is, it will always return
accurate hydrometer reading when checked at 68° F. Let the temperature
drop to 60°F and you'll get a higher reading (82 percent for an actual
80 percent mix; let it climb to 80°F and your reading will drop to 77
percent for the actual 80 percent mix.
To combat this problem refer to the accompanying chart which lists actual
percentages of nitro at various temperatures and hydrometer readings. As can
be seen the variations in the true percentage are quite significant.
FUEL TEST CHART
Test hydrometer reads 100% at 68° in known pure nitro.
TEMPERATURE OF FUEL- (°F)
|
True % Nitro |
40° 50° 60° 68° 70° 80° 90° 100° 110° 120 |
|
100 98 90 80 70 60 50 40 30 20 10 |
106 104 102 100 99 97 94 92 90 87 104 102 100 98 97 95 93 90 88 86 97 94 92 90 89 87 85 83 80 78 86 83 82 80 80 77 75 73 70 68 75 73 71 70 70 68 65 63 61 59 66 63 61 60 60 58 56 54 52 50 55 53 51 50 49 48 46 44 42 40 45 43 41 40 39 37 35 33 31 30 35 33 31 30 29 27 25 23 22 20 27 25 22 20 20 18 17 15 13 11 20 16 13 10 10 9 7 5 3 1 |
EXTREMES of temperature can play havoc with nitromethane power output
and provide for false hydrometer test readings. Graph above shows the effects
of temperature changes on nitro-completely accurate readings can only be obtained
with fuel at 68 degrees Fahrenheit.
KEEP IT RICH
Once again we stress as you increase the use of Nitromethane you must run
well on the rich side, even up to the point of the engine starting to misfire
on the run, regarding the cost of the fuel as an insurance against engine
failure caused by the increased power developed as the percentage is increased.
A constant check should be kept on the valve clearances as this will at once
indicate if by any chance a valve is stretching at the neck, both inlet and
exhaust being suspect when running at high power levels.