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Jerry, theoretically, horsepower is horsepower no matter how it is achieved. The definition is rate of work or torque times velocity. Over the history of tractors, manufacturers did change displacement to get more horsepower. Often this was done by increasing stroke. Nearly as often, they increased bore. But the most frequent method to increase horsepower was by increasing the rpm and regearing. This worked very well if the engine had a flat torque curve with rpm which almost all engines do below 2500 rpm. And also, they increased compression with every new model. It does make a difference what you want the horsepower for. If is in a tractor pull, I'd go with cubes. If it is in a race car, I'd go with compression as the compression increase greatly improves acceleration. If it is in a tractor that is to be used for field work, I think they are nearly equal with the edge to compression. Cubes will give you more pull power. Compression helps a lot more for economy and it helps for pulling as well. The theoretical calculation of engine economy is based almost entirely on the compression ratio - the higher the compression, the greater the efficiency. Displacement is not in the equation. So, if I'm farming, I'd probably do both with the emphasis on compression (economy). If I was doing it for tractor pulling, I'd lean heavy to displacement but I'd probably increase compression, too. If it is a race car, I'd max the compression and do some increased bore as well. I wouldn't increase stroke on a racing engine if it is near 4". And I wouldn't change bore if it was over 4.0" as this increases the predetonation. If bore and stroke are max, then raise compression and get better fuels.
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