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Steam Engine Torque

The torque, or twisting force an engine is capable of producing is more of a measure of actual engine power than horsepower. A gasoline engine will produce torque in the range of 250-400 lbs. when the engine itself is over 300 cu. in. and over 200 horsepower. Steam and gas horsepower are not the same.

Most automobile engines will not reach maximum torque until they reach 2200 rpm. A steam engine can reach maximum torque when the piston is hardly moving. It works like this:

A gas engine is powered by a certain amount of compressed fuel and air. The pressure in a gas engine that creates torque increases as the engine turns faster and compresses proportionally more fuel and air. At lower rpms the poppet valve system used in gas engines limits the amount of pressure that can be created as the intake and exhaust valves are quite often open at the same time (valve overlap).

At higher rpms you still have valve overlap. It just isn’t as noticeable as the fuel-air mixture doesn’t have as much time to enter the intake and leak out the exhaust valve before both valves close and ignition takes place.

A steam engine can allow steam into the cylinder and press against the piston depending strictly on the pressure of the steam coming from the boiler. As the pressure builds, the piston moves. If the piston is pushing against a load, the load moves as the pressure increases. If the load is too much for a gasoline engine, the engine dies (quits running). When a steam engine is subject to a load that is "too much" the engine doesn’t die. It breaks.

Steam itself is literally unstoppable and, at pressures past what metal can endure, irresistible. For an example of the power of steam, consider the largest steam explosion in the history of the United States: Mount St. Helens.

 


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