Reduces the ET by .000 RCH

You are asking a question discussed many times before. Usually no one has any real proof to support a performance increase. You are correct, it has to be an improvement, but evidently not enough to notice. Just the weight savings, should be a plus.One thing is the high dollar items can be thought to be better built/higher quality, and built the next size larger dia, which is a huge improvement in increasing the shafts "critical speed" ( jump ropes). I have a few Alum Glued MW shafts, and if money was not a big concern, I would go CF, which when it fails, has a lot less destructive energy to deal with and becomes flexible strands/fibers, FWIW.

PS, "is it worth it dollar wise?" Only one person can answer that.

So carbon fiber is out, but what advantages are there going to aluminum over steel, if any? Even the weight difference should account for something. Hey Poly, you seem to be in agreement with outlawssaa that there is no advantage. In the automotive world, I see you as Steven Hawking's cooler brother. My driveshaft is very close to stock length, so there should be a considerable amount of weight loss using aluminum over steel. Why would this not be a benefit ie: why won't the car be any quicker?

So carbon fiber is out, but what advantages are there going to aluminum over steel, if any? Even the weight difference should account for something. Hey Poly, you seem to be in agreement with outlawssaa that there is no advantage. In the automotive world, I see you as Steven Hawking's cooler brother. My driveshaft is very close to stock length, so there should be a considerable amount of weight loss using aluminum over steel. Why would this not be a benefit ie: why won't the car be any quicker?

The carbon shaft won't damage the car when it breaks. Steel and even aluminum will both beat your car all to hell underneath

Weight is weight............If I can buy a part that is just as good or better, plus it weighs less.........that's what I use. Ounces make pounds and 1 pound savings here and there, eventually make 10 pound savings and so on. Nice Carbon shafts can be bought in the $800 range from certain places and a good alum shaft from Denny's etc will set you back $500. So it depends on whether the extra $300 is worth it to you from a little weight and additional safety aspect

Theory says the engine has to accelerate two different things.
1. The weight of the car.
2. The rotational inertia of everything on the car that accelerates when the car accelerates. That means engine rotating mass, flywheel and all clutch parts, all transmission parts involved at any one time, the driveshaft, ring and pinion, axle shafts, wheels and tires, brakes.

In Mark's Mechanical Engineering handbook, 7th ed., there is an interesting statement that tfor a popular car of I believe the '50s, with a total gear ratio of around 14:1 the engine spend as much power accelerating the rotating parts as the static parts.

The issue is that rotational inertia is influenced by the distance of the mass from the rotational axis, I believe by something like the 4th power. Realistically this means that as the diameter decreases, the rotational inertia decreases rapidly. So the contribution of things like axle shafts is usually neglected. So with shafts in transmissions. Acceleration is change in rotional speed divided by time. If you think about it you see that the engine parts change rpm much more than say a driveshaft, which accelerates more slowly than any other shaft except the axles themselves. Plus the driveshaft is maybe 4: in diameter, which means that even though it has length, it doesn't contribute very much to the rotational mass the engine is trying to accelerate.

So the real contribution a lightweight driveshaft makes is to static mass reduction. This is, I believe, why the auto manufacturers are making them out of aluminum. Every pound of vehicle mass requires energy to move and the CAFE standards are tightening.

There's another factor that has been mentioned and that is stiffness. A driveshaft in a drag car is long and slender and unsupported on both ends, so it is prone to vibration. Building a stiffer driveshaft is easier when using a lightweight material like aluminum or carbon fiber, as it can be made larger in diameter for the same weight, and larger in diameter is better than wall thickness for increasing the resonant frequency.

Thus, using a lightweight driveshaft won't really make a difference in acceleration due to reduction in rotating mass, but it will make a difference in reducing static mass. It will also allow a stiffer driveshaft which will be safer. Go as light as you can afford.

R.