Efficiency is a measure of the engine's useful work output per the amount of fuel consumed. As the load is increased the efficiency typically increases and becomes a maximum at about 80% of the engine's maximum output. As load is increased to greater than 80% the efficiency tends to decrease. At idle the engine is consuming fuel however, the engine is not connected to an external load. Since there is no useful work output, the efficency is zero. The only engine load is to over come friction, drive the cooling pump/fan, alternator, etc. Once an external load is applied we have useful work output and efficiency, however fuel consumption will increase to produce the additional power. In a similar manner as a truck's weight is increased the engine may be operating in a more efficient load range, however the fuel mileage will decrease due to the additional power production required.
Heavy truck engines are typically designed for lower RPM operation, which in part provides for increased life. HP = (torque x rpm) / 5252; if power is to remain the same then the engine's torque output must increase. The higher torque can be obtained by increasing the engine's displacement and/or cylinder pressure. Given equal HP of a high speed or low speed engine the driving force (torque at the rear alxe) can remain the same by selection of the proper gear ratios in the transmission/rear end.
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Today's Featured Article - Sunday Drives - by Cowboy. Summer was finally upon us here in Northern Maine. We have two types of industry up here, one being "Forestry" (Wood Products) and the other "Farming" (Potatoes). There is no shortage of farm tractors and equipment around here! I have been restoring old Farm Tractors for the past 6 years, and have found it easier and less expensive to hit all the auctions and purchase whole tractors for parts needed. My wife who works at a local school, and only has weekends and summers off, while on t
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