Is this Driveshaft guy smoking crack or what?
#31
Ive had a 4" AL, a 5" AL, and a 3.5" steel from them, all quality parts.
Steel has a higher critical speed due to the much higher modulus of elasticity of the material; thats why they can afford to be a smaller diameter for the same application. AL is lighter, so it saves you a few hp, but you need a larger diameter. The weight of the shaft does not matter as far as critical speed is concerned. The only thing that matters for critical speed is modulus of elasticity, diameter (inner and outer), and length.
Steel has a higher critical speed due to the much higher modulus of elasticity of the material; thats why they can afford to be a smaller diameter for the same application. AL is lighter, so it saves you a few hp, but you need a larger diameter. The weight of the shaft does not matter as far as critical speed is concerned. The only thing that matters for critical speed is modulus of elasticity, diameter (inner and outer), and length.
#34
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Well i called them back and spoke to a different guy. I gave him the measurements they asked for and spec of my truck. He said at 62 inches seal to center a 4in AL would be fine. He said the critical speed would be 7200. I went ahead and got the shaft built with 1350 ujoints. The rear ujoint is a bastard 1350/gm inside clip 1330 (or whatever the stocker is). That way when i redo my gears i just have to swap out the rear joint and pinion yoke for a 1350 one. The new shaft should be here early next week just in time for my swap next weekend.
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