[FrankieT/A]

Originally Posted by Formulajones

The critical speed is why the lighter weight driveshafts have an advantage.

It's one reason OEM went aluminum. You see this on trucks a lot. With there longer shafts, the older trucks used carrier bearings so they could run 2 shorter steel shafts. When they got away from the carrier bearing and started using one piece driveshafts they went aluminum. The lighter weight works in your favor, has a higher critical speed before it starts the whipping action. Plus you gain the benefit of less rotational mass that doesn't zap HP.

If you look at the PST chart posted by Will, you'll see the aluminum has a higher critical speed than even the chrome molly.

3.5 vs. 3.0 makes a big difference in critical speed...

The thing that worries me about aluminum is the strength of the ears where the U joints mount. They look like they would break right off doing a hole shot.

[Formulajones]

Originally Posted by FrankieT/A

3.5 vs. 3.0 makes a big difference in critical speed...

The thing that worries me about aluminum is the strength of the ears where the U joints mount. They look like they would break right off doing a hole shot.

They are good for 1000 hp so if you break one with a hole shot you're doing something.

In fact GM still uses them on their duramax's, as well as the other OEM's on their diesels and look at the power those things are making these days. Especially the torque. Couple that with the fact that they weigh over 3 tons.

My Duramax is making over 700 ft lbs. at the tire (newer models are more now) and it weighs 7000 lbs. empty with no one in it. That aluminum shaft is holding up fine. So I had no qualms putting one in my 600hp Chevelle. I'll never break it.

[ta man]

Originally Posted by Formulajones

They are good for 1000 hp so if you break one with a hole shot you're doing something.

In fact GM still uses them on their duramax's, as well as the other OEM's on their diesels and look at the power those things are making these days. Especially the torque. Couple that with the fact that they weigh over 3 tons.

My Duramax is making over 700 ft lbs. at the tire (newer models are more now) and it weighs 7000 lbs. empty with no one in it. That aluminum shaft is holding up fine. So I had no qualms putting one in my 600hp Chevelle. I'll never break it.

Not really apples to apples comparison ...Trucks have 5 inch diameter aluminum shafts to handle the torque..I would guess your Chevelle has a 3.5?

[Formulajones]

Originally Posted by ta man

Not really apples to apples comparison ...Trucks have 5 inch diameter aluminum shafts to handle the torque..I would guess your Chevelle has a 3.5?

Chevelle has a 4" shaft and I believe they build it with thicker wall tube as well. Got it through PEM if you want to check out details. Prices aren't bad either.

Considering what those trucks put those shafts through with towing 15,000+ lbs and the torque the diesels make, they'll take some abuse for sure. I've seen the inside of those aluminum shafts for the trucks too, they aren't very thick wall tubing at all.

I'm not going to break it.