From Kinsler Fuel Injection, Inc. 1834 Thunderbird Troy, MI 48084
How to Check the Fuel
Put enough of the liquid to be tested in the glass cylinder to allow the hydrometer to float. Hold the thermometer in the liquid so the bulb is submerged but not touching any part of the glass cylinder. Carefully sight across the bottom of the meniscus and read the hydrometer. The hydrometer MUST be floating freely, not in contact with the glass cylinder or your fingers.
Octane is a unit of measurement used to rate a fuels ability to resist detonation. Detonation (spark, knock, ping) is the tendency of the fuel to explode violently in the engine rather than burning smoothly. If the fuel detonates, the pressure in the combustion chamber rises so fast and high that it is like beating on the top of the piston with a hammer…this is a primary cause of piston, rod, and bearing failures. The higher the octane rating the higher the resistance of the fuel to detonation. Racing gasoline is blended to provide additional octane rating, not more energy. In fact, all grades of gasoline have about the same amount of energy per pound. Increasing the octane can get more power, since more compression or spark advance can be used. Note: too much octane can slow the burn rate of the fuel causing a loss of power.
There is a big difference in specific gravity between various brands and grades of gasoline, often even between two batches of the same brand. The typical range of premium automotive pump gasoline is .730 to .760; aviation gasoline is .680 to .720; some unleaded racing gasolines are as heavy as .790. Many blends of pump gas now contain as much as 10% ethanol. These blends generally fall into the heavier specific gravity range.
For example: Unocal 76 ® unleaded racing gasoline .788 @ 59°F (15°C).
Unocal 76® leaded racing gasoline .728 @ 59°F (15°C).
The specific gravity of pure methanol is .792 @ 68°F (20°C). Methanol, methyl alcohol, or wood alcohol (CH3OH), is usually made from natural gas. It was first discovered in 1823 by condensing hot gases from the burning of wood. It has been the fuel for Indianapolis 500 race cars since 1965. Methanol has the ability to absorb water, even right out of the air. Keeping your fuel sealed will help prevent contamination. Adding water to alcohol will increase the specific gravity. High levels of water contamination will cause the alcohol to normally get cloudy. Loss of engine performance will typically occur before contamination reaches these high levels. Fuel should be checked with a hydrometer before using it, maybe even before you leave your supplier, just to be sure to avoid any problems. Methanol is extremely corrosive to aluminum and magnesium; great care should be taken to keep this reaction to a minimum. The fuel system components should be of materials that do not react with methanol (stainless steel, brass, etc.) or should have a protective coating. Methanol crystallizes when it dries, this dried methanol does not readily dissolve. The fuel system will need constant attention. When not in use, the fuel should be drained out of the system. Flushing or “pickling” with gasoline is a common practice.
The specific gravity of ethanol is .815 @ 68°F (20°C). Ethanol, ethyl alcohol, or grain alcohol (CH3CH2OH), is a liquid derived from corn or other grain, other agricultural products or waste. Because ethanol is corrosive (due to oxidation), the same modifications must be made to the fuel system as methanol to protect the fuel systems components.
In the 1880s, Henry Ford built one of his first automobiles-the quadricycle-and fueled it with ethanol. Early Ford Model T’s had a carburetor adjustment that could allow the vehicle to run ethanol fuel that was produced by America’s farmers. Ford’s vision was reportedly to “build a vehicle affordable to the working family and powered by a fuel that would boost the rural farm economy”. However, in the past due to whatever reasons any alternative fuels other than gasoline were suppressed. Today, we are seeing the return of alternative fuel vehicles.
The specific gravity of pure nitromethane is 1.139 @ 60-70°F. Nicknamed ‘nitro’ is chemically CH3NO2. Pure alcohol (.792 @ 68°F) is considerably different than nitromethane; it is easy to determine the percentage of nitromethane in alcohol by measuring the specific gravity of the mixture. Adding nitro to alcohol will increase its specific gravity. A table can be set up to show the percentage of nitromethane versus specific gravity.
The procedure is only slightly complicated by the fact that temperature affects the specific gravity, since any fluid expands as it is warmed, and therefore has a lower specific gravity. For example, a 60% mixture of nitro and alcohol and heat it, we know that it is still a 60% mixture, yet its specific gravity is lower.
Some brands of nitro hydrometer kits are sold without correction tables. Errors of 5% are common if no temperature correction is used. For best engine performance the nitro percent mixture should be kept within one or two percent of what the engine was tuned for.
Note: Mixing nitromethane creates a mild endothermic reaction, which absorbs heat from the mixture, thus cooling it (this is the opposite of most reactions, which give off heat). The maximum affect is with about a 50% mixture, which cools approximately 15°F.