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On Tue, 24 May 2005 21:54:29 GMT, Thomas Tornblom
-to-reply wrote: Steve writes: Sport Pilot wrote: Why the obvious apple and orange comparision? To refute the statement that "more speed is more power." You need to compare engines of equal size. OK, Lets do it! Dodge 5.9 Liter v8 gasoline engine: 230 horsepower at ~5000 RPM Compared to: Dodge/Cummins 5.9 Liter turbo-diesel engine: 325 horsepower at 2900 RPM More speed is NOT more power any more than more torque at the same speed is more power. One BIG factor is being forgotten here. The diesel is turboed. This makes it roughly equivalent to an 8 liter engine at about 6psi boost. Any combustion engine produces power in proportion to the amount of air consumed. On a diesel it does not necessarily "consume" all the air that goes through it - but the maximum power output is definitely limitted by how much air can be put through it. A turbo can eisily double the amount of air an engine pumps through it at a given speed. Running an engine at double the speed also increases the amount of air going through the engine - not quite double due to reduced volumetric efficiency at speed. Double the CFM gives double the horsepower, before factoring in frictional losses and / or pumping losses. A naturally aspirated diesel engine generally produces less HP per unit of displacement, but more torque at low RPMs due in part to less pumping loss (no air throttle) uh? More torque at the same speed *is* more power. power = torque * speed Had the gas engine produced the same torque at 5000 rpms as the diesel do at 2900, then it would have had about 560 hp at 5000. Thomas |
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