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.
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.
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|
|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.