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To assist the radio controlled model car racer in interpreting, amongst other things, the dynamometer (dyno) tests, we have the following descriptions about the various units used in measuring and determining the various characteristics of an engine.
After reading them you will hopefully be able to fully make sense of the graphs provided on this site. |
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| Horsepower |
| A measurement scale used to express the power available from an engine that is usually measured at the output shaft of the engine. It can also be measured at the wheels, but some drive trains would give higher results than others due to efficiency differences. |
| The horsepower scale was originally devised by James Watt as a way of conveying the amount of work a horse could do in a certain amount of time. He apparently observed pit ponies at work and determined that a horse could do 33,000 foot-pounds of work in one minute. This means that the horse could move the equivalent of 33,000 pounds a distance of one foot in one minute. |
| Note the three parts to this equation, namely foot, pounds and minute, so the 33,000 can be mathematically expressed as moving 330 pounds a distance of 100 feet in one minute (330 x 100 = 33,000) or 33 pounds a distance of 1000 feet in one minute (33 x 1000 = 33,000). The same mathematics apply for calculating the power for seconds; 33,000/60 = 550 foot-pounds per second. Foot-pounds is normally abbreviated to ft/lb. |
| The foot-pound scale can be translated into various other units and is equivalent to 746 watts or 2,545 British Thermal Units (BTU). |
| BHP - Brake Horsepower |
| Brake horsepower describes the measurement unit of the power available from an engine (or motor) that a dynamometer (dyno) determines by placing a braking load upon (usually) the crankshaft and calculating the amount of resistance which the engine can produce. |
| Dynamometers don't directly measure horsepower, they measure the torque of the engine, the brake horsepower is then either manually or automatically calculated, depending on the sophistication of the dynamometer. |
| Torque |
| Torque is a force that usually turns things. When you put a spanner (wrench) on a nut and press down you are applying torque to the nut. The combustion of the fuel/air mixture also generates torque to turn the crankshaft and can be measured in inch-pounds (in/lb), foot-pounds (ft/lb), but is now more commonly measured in the SI (Standards Institute) unit of Newton Meters (N/M). |
| This measurement scale is composed of two parts, the Newton is the force and the meter is the distance from the centre of rotation. Like the examples given above the two are mathematically proportional, that is; 1 Newton at one meter = 2 Newtons at half of a meter. |
| Brake Mean Effective Pressure |
| Brake Mean Effective Pressure (BMEP) is used as an indicator to express the average engine efficiency of all engines, be they two stroke or four stroke. BMEP is a function of the temperature of the burning gases in the engine cylinder and is used to show how efficient the engine/exhaust combination is. |
| Put simply, if a pipe/engine combination can make better use of the fuel/air mixture, it will produce more heat in the combustion process and will therefore produce the same amount of power (if not more) as another pipe/engine combination whilst using less fuel. This is beneficial for such as long finals, where pit stops are either not allowed or take precious track time. |
| Summary |
| You should now have a better understanding of the terminology regarding model car engines. |
| Further Information |
| For help with the terms used throughout this series of pages, please see the Engine Terminology section. |
| If you have any comments or suggestions about this or any of the other R/C car content on the RcTek site, please feel free to ask them on our On-line Forum |
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| Unless stated otherwise all images and content are Copyright (c) RcTek 2000/2001 |
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