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Terms & Definitions

Motor Octane (MON):
(a) CFR Tested @ 900 RPMs, timing is varied with compression ratio, fuel is preheated to 300 degrees Fahrenheit, intake air is preheated to 100 degrees Fahrenheit. (b) Motor Octane, measured under varying load is definitely the most representative octane measurement for Real World Hi-Performance Engine Applications. (c) The closer the Motor Octane number to the Research Octane number the more stable the fuel is throughout the RPM range (see the Octane Differential in the chart above). This is very critical when running higher that 7500+ RPMs engine speed.
 
R+M Octane (R+M):
(a) This method of measurement consists of adding together both the motor and research octane numbers and then dividing by two. (b) This is the number in that yellow box that you see on the gas pumps. (c) This number should only be used when determining which fuel to use in your street car or tow vehicle. This method is NOT intended for correct use in your racing engine.
 
Research Octane (RON):
(a) CFR tested @ 600 RPMs, fixed timing at 13 degrees BTDC, fuel temp is not controlled and intake air is varied with the barometric pressure. (b) This is basically a No-Load test and this number should never be used to determine which fuel to use in your race engine.
 
Specific Gravity (SG):
(a) This is the weight of fuel compared to water, water being at 1.00. If race fuel is .750 (specific gravity) it would weigh the weight of water. If water at 60 degrees Fahrenheit weighs 8.125 pounds per gallon (ppg), then race fuel at .750 will weigh 6.09 (ppg). (b) The less dense the fuel (lower specific gravity) the higher the BTU content and the better the stability of the fuel at higher RPMs. (c) The lower the specific gravity of the fuel, the more crucial the jetting becomes, and the easier it is to run the engine lean, possible causing internal damage. (d) The combustion speed is determined primarily by the pressure (density) of the fuel mixture.
 
Lead Content (LC):
(a) When lead is added to fuel, the knock resistance (anti-knock value) is increased. Lead is also used to increase the octane to a higher number.
 
Consistency:
It is very important that the fuel you use maintains it's purity and consistency regardless of which brand fuel you use. Try NOT to purchase fuel that has been stored in bulk storage tank, or transferred from one bulk location to another. Bulk fuel storage tanks have a tendency to sweat or secrete moisture, therefore changing the consistency or purity of the fuel. If at all possible buy your fuel in a factory sealed drum (the cost is usually higher) but it is well worth it in the long run.

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