00pooterSS

iTrader: (40)

One thing to be aware of with driveshafts. Stronger doesn't always mean it'll take more speed. Make sure when you get a single shaft done it will handle the mph you're going to run it to.

Even several drive shaft makers don't speak this language. I called a few local shops and asked if they make a shaft with a higher critical speed, they all said yeah we make a strong one. I don't need strength. I'm no where near twisting one, don't make enough power or get enough traction. And they all said yeah it's stronger. You can have strong and a low critical speed so make sure who ever does your shaft understands BOTH strength and critical speed.

kaze_v8

That confuses me.
If lower critical speeds are whats causing these DS to snap in half, how would strength not result in a higher critical speed.

I ask because of this.
I have an AWD truck, i plan on launching it hard, but still be able to make a 1/4 mile pass considering i will trap close to 120mph..
So basing it on your theory id need a DS that is both strong enough to handle my hard AWD launches and a DS that can get me to 120+mph?
If so, that means i have two issues now, instead of one.

00pooterSS

iTrader: (40)

No problem mane.

This is a good calculator to use and a good, short, write up too.

Driveshaft Critical Speed

00pooterSS

iTrader: (40)

It is confusing. And that's why even some of your basic drive shaft shops don't get it. Stronger usually comes from thicker tubing, which lowers the critical speed capability.

And on your sentence about the theory part, yes that is correct. You need one that is able to handle the power and speed. Which your stock ones probably will. And by the way it isn't my theory, it's info gathered from testing. It also applies to all sorts of spinning shafts used in manufacturing etc.


Copy and pasted from the above link

Critical Speed:
This is the probably the most influential factor in driving the purchase of an aftermarket driveshaft. The critical speed of a spinning shaft is described as the lowest speed which excites the shaft at it's natural frequency of vibration. This will cause the shaft to bend under the stress of vibration coupled with the centrifugal forces due to the rotation. In english, this means the shaft will vibrate very badly and possibly take a permanent bend (if not destroy the car in the process) as the critical speed is exceeded. If you use the calculator to predict the critical speed of a shaft, you can clearly see that lighter materials with higher modulus of elasticity give higher critical speeds. So do larger diameter shafts with thinner material thicknesses. Unfortunately, there is a limit to the diamter of shaft you can put in the car, so stronger lighter materials were developed to make stronger and faster spinning shafts.

On the bold part. Thinner material gives you a higher critical speed, but thicker increases strength.

kaze_v8

Interesting...
Its starting to make sense now

Bgbldodge

At some point the weight of the shaft becomes to much. It's a balancing act, no pun intended.

00pooterSS

iTrader: (40)

LOL yup.

00pooterSS

iTrader: (40)

I don't know if 450-500 will twist one. Hopefully someone experienced with that power on that truck will chime in. The harder you launch and the more it hooks the more likely it is. If you aren't doing hard launches with the tires dead hooking you probably be okay. But you also have to consider how fast you'll go with it. Hence all the above posts.

Carbon fiber is excellent, if you can afford it go for it.

IF it is the right length and has the right yoke on it for your transmission. You can. But if you go from one piece to two piece you will also have to have a cross member to bolt the center support bearing to, that is on the 2 piece shaft.

00pooterSS

iTrader: (40)

For everyone.

Just call Dennys Driveshafts, The Drive Shaft Shop (DSS), or Alldrivelines.com (performance driveline) if you want it right the first time. That's what I would do.

Mileguru

These are two good shops too:
Performance Driveline
Driveshaft Specialist Inc