It's interesting to play with the numbers. Take two engines with 50 cubic inches per cylinder, one with a 4.0" bore, 4.0" stroke and the other with a 3.5" bore, 5.2" stroke. If you calculate the theoretical torque that the piston can apply to the crankshaft for a given cylinder pressure you'll find that it is exactly the same for both engines. (The increased "leverage" of the longer stroke is countered by the greater "push" of the larger piston's area.) The typically better low end power characteristics of the small bore, long stroke engine are due to the fact that low speeds is the only place this engine can operate due to the resulting small valves and piston speed limits and it is therefore tuned accordingly. It only makes sense for a manufacturer to tune the larger bore, shorter stroke engine to take advantage of the better breathing capabilities and higher speed potential in order to provide more power. The cam profile and timing that provides this often comes at the expense of low rpm torque but since power, not torque, is what determines how much work an engine can do in a given amount of time it is a worthy trade-off. Which is better or worse all depends on what you're doing and what you prioritize most.
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Today's Featured Article - Earthmaster Project Progress Just a little update on my Earthmaster......it's back from the dead! I pulled the head, and soaked the stuck valves with mystery oil overnight, re-installed the head, and bingo, the compression returned. But alas, my carb foiled me again, it would fire a second then flood out. After numerous dead ends for a replacement carb, I went to work fixing mine.I soldered new floats on the float arm, they came from an old motorcycle carb, replaced the packing on the throttle shaft with o-rings, cut new ga
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