Because they are thin walled and large diameter when compared to a steel one which is solid and small diameter. They used the aluminum ones because they handle Torque better(because of their diameter) and for long DS like 82" they don't need to go with a two-piece DS like they would if they used steel (steel is too heavy and it sags if left as one piece). When they are that long, one piece and large diameter they start to flex and wobble at high revolutions. My truck's underbelly took a bit of a beating because I was negligent to heed other people's advice and there are some carnage pics running around this forum of people who's Aluminum DS decided to split apart during high speed dyno runs.

 

Hey mike, do you have a picture of your truck?

 

my dad had a vega. he had a blown and bottle fed 454 in it. it made over 1000 hp. he had a custom steel driveshaft on it and it ran well. he wanted to free up a little more hp and put an aluminum on it. first time at the track and it shattered and came through the floor pan. we ended up going back to the steel and figured a driveshaft loop would be a good idea. i say dont use aluminum drive shafts. not worth "carnage" they can cause at high speeds (and they are like 500-800 bucks i think)

 

Thats what correction factors help with. It helps correct for weather conditons.

 

exactly,sae corrected numbers adjust to 75 degrees and i think 51% humidity.if your numbers are std they probably would be better if the sae correction factor would've been used.jmo.

 

not bad for the numbers you got. heat def hurt you



the driveshaft may not have been chosen correctly or was over the range of power recommended. given steel and alum driveshafts the alum one will take higher rpm because its lighter and also because larger diameters are used. yes wall thickness would be greater then steel but take a look at critical speed charts (read failing point for given driveshaft) a 4" dia alum one 48" long will go 10k rpm where a 3" steel one will only do 7500. step up to carbon fiber like the pro stock guys and youd be able to go 11,300. it has to do with the natural frequency of the material and vibrations it is dealt with.

 

Heat doesnt hurt, the correction factor ADDS power to the power and toque curve from what it actually reads based on what the weather station sees.

Common correction factors;

SAE, which is more realistic, is based off of 77*F, no humidity, and a 29.23" Hg

STP(aka:STD) is based off 60*F, no humity, and 29.93" Hg and bassically adds 4% accross the board vs SAE. So if you made 450hp (SAE) you would make about 468hp (STP)

STP is what most magazines and dyno shops use to get high numbers so everyone can post big numbers in their sigs. And then you buy more parts becasue they "must" be great because my dyno numbers are so good.

 

I also had my truck dyno done at Colvin's. It was my first ever dyno run on my 04 Rumble Bee. Stu with Inertia was tuning the new heads and cam 12 runs in 2.5 hrs. We ended up with 348 hp and 368 tq.