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Two stroke vs.four stroke. I understand how they both work, but I wonder if EMD is hitting on every stroke, and GE is hitting on every other stroke, does EMD have less displacement. If the displacement is the same wouldn’t EMD have an advantage.
A 645 engine has slightly less displacement than a 251 or an FDL, but I don’t think that it makes that much of a difference.
The answer is not as easy as it seems at first glance. A two stroke engine only gets power from about 1/2 of the down stroke. The rest of the downstroke must be used for purging the exhaust and part of breathing in new combustion air. A four stroke engine gets power for the whole downstroke on the power stroke.
Also the first part of the upstroke on a two stroke engine the exhaust valve and inlet ports are still open for fresh air to blow in. So there is no compression for part of the stroke. In a four stroke engine the air is compressed for the entire stroke.
And the engines can be run at different speeds. In fact that has been one of the major problems with placing an EMD diesel engine in an old ALCO. The GM engine being installed and the original equipment GE generator were designed to operate at different rpms.