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Date: Fri, 19 Feb 1999 13:43:12 +0200
From: "Roy Björkstrand" <nospamroilonopsamut.fi>
Subject: Re: torque vs. horsepower


Julian Sweet wrote: > Could someone give me a technical, yet concise explanation as to why > torque is responsible for acceleration and horsepower for top speed? I > understand that torque is a rotational force and horsepower is power -- > but explain the connection please.... Easy expanation, possible??? Power is work done relative to the time. Torque is not. There is still one term more - mean effective pressure. Both the torque and the power can be calculated from it. It also tells what kind of mechanical and thermal stresses there are. People usually say that torque for acceleration and so on. Any car is a kompromice between many many things. One of the biggest is the transmission. With five gears it is impossible to obtain the best performance in all situations (you have eighter too much revs or too low revs). If the engines character is more like high AND WIDE torgue (long stroke, big cylinder capacity), you have during the acceleration quite much power in any gear and on any RPM. On the other hand if your engine has a short stroke + many small cylinders (power but not torque), your acceleration might be lousy because you don´t have power at all on lower RPM (if your gearbox is designed badly). Though your top speed could be high because your gear ratio corresponding to the power is good at that speed. It is not easy to explain what I´m meaning. I bet you can find some litterature about engines and what kind of demands there are for the transmission ratios. For every car you can draw a "drivepowergraph" (I don´t know what it is in english). It contains graphs about the power engine can create on wheels on every gear. There are also graphs for all resistances (air, wheels, friction...). From combination of graphs you can estimate the top speed and how does your transmission ratios work (+some more). I think that that graph and some additional meterial about the definitions of power and torque could answer your question more thoroughly. Roy PS. I know that this was not a sientifically bullet proof explanation.

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