power to weight

[eric81]

My car weighes 2,380 with me in it, and spare tire and all. I am about 200 with clothes, tire is almost 10, jack and spare parts about 40 or so, and then I took off heat shield, put in aftermarket battery, (slightly less weight, maybe 3 or 4 pounds) and I have NOT added any stereo equipment. Now, I drive a 5 gear manual, so it is a little lighter than an auto, but all in all the same. I figure my car is pushing close to 110 hp, all parts and improvements in place, so the car is about 2100:110, or we could just say about 19:1. Not bad all said and done, but then there is the difference between dead weight and rotational weight, which I explained before, but will gladly do again.

First off, dead weight is the frame, body, battery, engine block, seats, windows, and anything else not rotating with the engine to make the car go. Then you have rotational weight, which is cams, pistons, crank shaft, pulleys, tranny, rims, tires, axels, a/c, alternator, and fun stuff like that.

If you take 5 lbs of dead weight off the car, like the spare tire, for instance (it is more than 5, but just follow me here), then your car might possibly get about .1 seconds faster on the 1/4 mile time, and maybe .5 mph faster. Now, take the same weight off of your pulleys (NST kit, for example, for just $240 or close to that), and you will get about .5 seconds or better, and easily achieve 2 or 3 miles faster on the 1/4 mile end.

How is this so? Well, it takes more energy to rotate something than it does to simply push/ pull it. There is this new thing (at least, it's new to me) called "knifing", which simply means "smoothing the edges on the crank shaft so they form a smooth edge, so the crack shaft can flow through the oil faster and with less resistance and weight" It costs a lot to have it done because the crank shaft has to be rebalanced, but the results in top end horse power, and the time it takes to rev the engine from idle to max, are incredible. If I ever get enough money to play with, that is one of the main things I would like to do to my car.

So, weight to power is not everything, just to be clear.

[dallas]

For revolving mass like flywheel. pulley, rims etc, the basic rule is :
each 1 lb is like 7 lbs of dead weight.

Example : If you save 2 lbs for your wheel and tire combo X 4 of them it = 8 lbs is like removing 56 lbs from the car.



is

Originally Posted by eric81

My car weighes 2,380 with me in it, and spare tire and all. I am about 200 with clothes, tire is almost 10, jack and spare parts about 40 or so, and then I took off heat shield, put in aftermarket battery, (slightly less weight, maybe 3 or 4 pounds) and I have NOT added any stereo equipment. Now, I drive a 5 gear manual, so it is a little lighter than an auto, but all in all the same. I figure my car is pushing close to 110 hp, all parts and improvements in place, so the car is about 2100:110, or we could just say about 19:1. Not bad all said and done, but then there is the difference between dead weight and rotational weight, which I explained before, but will gladly do again.

First off, dead weight is the frame, body, battery, engine block, seats, windows, and anything else not rotating with the engine to make the car go. Then you have rotational weight, which is cams, pistons, crank shaft, pulleys, tranny, rims, tires, axels, a/c, alternator, and fun stuff like that.

If you take 5 lbs of dead weight off the car, like the spare tire, for instance (it is more than 5, but just follow me here), then your car might possibly get about .1 seconds faster on the 1/4 mile time, and maybe .5 mph faster. Now, take the same weight off of your pulleys (NST kit, for example, for just $240 or close to that), and you will get about .5 seconds or better, and easily achieve 2 or 3 miles faster on the 1/4 mile end.

How is this so? Well, it takes more energy to rotate something than it does to simply push/ pull it. There is this new thing (at least, it's new to me) called "knifing", which simply means "smoothing the edges on the crank shaft so they form a smooth edge, so the crack shaft can flow through the oil faster and with less resistance and weight" It costs a lot to have it done because the crank shaft has to be rebalanced, but the results in top end horse power, and the time it takes to rev the engine from idle to max, are incredible. If I ever get enough money to play with, that is one of the main things I would like to do to my car.

So, weight to power is not everything, just to be clear.

[scape]

For revolving mass like flywheel. pulley, rims etc, the basic rule is :
each 1 lb is like 7 lbs of dead weight.

Example : If you save 2 lbs for your wheel and tire combo X 4 of them it = 8 lbs is like removing 56 lbs from the car.

it also depends where the weight is displaced on the wheels and tires. a 14 lbs wheel with weight mostly in the center and a 22lbs tire might take longer to spin up than a 18lbs wheel with weight in the center along with a lighter 18lbs tire...adversely a 14lbs wheel with weight at the lip, and a 22lbs tire might take the longest...
the farther the weight is from the spinning center, the more inertia you have to overcome...the smaller the diameter, the closer the weight is to the center

b/c all tires and wheels are different, I don't think there is a great rule of thumb, but there is a method for determining the actual values by spinning the wheel/tire and determining the moment of inertia, but I do not actually know how-- something to do with tieing a weight with a string and watching the weight fall (spinning the wheel with it)...
http://dev.physicslab.org/Document.a...ertiaWheel.xml

here's another method, using a pendulum and torsion bar: http://www.velonews.com/article/79893

I'm also not sure having a lighter flywheel necessarily means your car will be faster, it just means the engine can rev with a quicker response, both up and down-- you still have to push the same car around.
now having lighter but strong pushrods, cylinders, camshafts, etc., would be interesting for a higher redline; in which case that lighter flywheel would be pretty handy I bet