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good question. I'll try to answer ... (archive)

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Posted by KC ///M3 on April 30, 2000 at 23:39:50:

In Reply to: Re: my 2 pfennigs (sorry Sam L!) posted by M3 on April 30, 2000 at 22:27:19:

You are right, the pulley will do a little to help acceleration for two reasons: it frees up a little horsepower, plus it is lighter weight so the crankshaft has less trouble turning all the accessory pullies. However, a lightweight flywheel will have a greater impact on acceleration because of rotational dynamics.

Take a bicycle wheel for example: there are 4 basic parts, the hub, rim, tire and spokes. Reducing rotational mass is one of the holy grails in cycling, because lighter wheels take less energy to turn and so accelerate faster. However, it is important where that weight reduction comes from because the radius figures into the equations of motion. Reducing the weight of the tire, rim and spokes by, say, 100 grams will have a far greater effect than cutting 100g from the hub.

So it is with the crank pulley and flywheel. Both attach to the crankshaft but they differ in mass and diameter.

Relatively speaking, the crank pulley is much smaller than the flywheel, both in mass and diameter. A lightweight pulley might cut 5 lbs or so, however this is like cutting weight from the bicycle hub, the effect is not too large. A flywheel is a lot larger than the pulley. Also, a lightweight flywheel will cut more than 10 lbs off the stock one. Less mass @ greater diameter = greater effect.

That is why the flywheel has a greater impact on acceleration than the u/d pulley.

Hope this helped a little.

Ken


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