PorscheG96

Yes, he wants me to buy a 911.

PorscheG96

Got it, thanks. Thinking it over and I have an idea.

Cole

Does anyone have any idea of the real forces applied to the tube?

I would imagine with solid or semi solid modern motor and trans mounts along with maybe even a small additional mount for the transmission and motor that the torque on the tube could be greatly reduced. Which would allow for all sorts of options for taking weight off the tube

95ONE

Global tech is where I get my aluminum tubing.. Its the cuts and shipping that cost more than the tube...

Eric_Oz_S2

Those tabs are not present in the ROW spec cars. I guess a lot of US safety regs come from an earlier time where seat belts weren't mandatory to use in the US? Never mind that you only need lap belts in the back

J1NX3D

the tabs are there on my '86 n/a

Oddjob

Whats the grade of the tubing?


Also, anyone know the wall thickness of the stock steel tube?


Not too hard to compare. In general aluminum weighs about 1/3rd of carbon steel and has about 1/2 the strength, but really need to compare the grades as there is a huge range of yield strength properties.

My guess is that the primary/priciple loading will be torsional shear. A 3" diameter, thick wall pipe is pretty rigid. Unlikely the sheet metal tub will add any stiffness if solid mounted to the drive train, more likely the otherway around - the drive shaft will stiffen the chassis.

As far as fatigue life of aluminum, as long as the tube wall is thick enough, I would worry more about the cyclic shock loading on the cast alum. suspension parts. I think if you keep the stress levels below 10000-15000 psi, I think you avoid much of the perpetual fatigue life failures in aluminum. And using aluminum in structural applications is pretty proven engineering. Look at the age and fatigue in the aero industry. How many hours are on those B52 air frames?

95ONE

6063 ASTM-B221. Not a super strength Aluminum by any means.

I just cut mine off the rear cast aluminum trans housing from the tube. Extremely interesting find on that thing.. I'll not get into it.. BUT. the steel is extremely soft and easy to cut with a sawzall. The wall thickness is about a .225 inch.. BUT.. I think the wall thickness on the the 968 or the 928 is very thin. I have nothing supporting, just remembering a picture of a 968 or 928 torque tube that actually has a portion cut out from the factory.. I could be getting senile So, the actual wall thickness is not really something to lay any rules down by.

adrial

I am an ME and basically agree with Oddjob. I would use 6061-T6, weldable aerospace grade Al. It is critical to HT aluminum post-welding to get it back to T6 to regain it's full strength.

I wouldn't weld an aluminum tube directly to the cast aluminum (unknown which aluminum). Welded aluminum isn't the best to begin with, welding to a porous casting is that much worse.

If you leave a flange on either end of the Torque Tube and use the same material for the flanges and the tube, you should be able to make it work. You're going to want to keep the stresses a bit lower in the welded area due to porosity, etc...

Only way to know is to start doing some numbers... which I do enough of at work

95ONE

I'm coming to the conclusion that Aluminum is a good budget 20lb weight loss... BUT.. the work involved is quite intense. If one should go through all that damn work to make it proper.....I say spend the $1000 on carbon. 30lb weight loss and zero worries about stress. (As long as you get The proper cross sectional weave for torsional forces.) I think the original maker of these aluminum ones were selling them at around $1500 ea? more maybe? (Worth every penny of work in my opinon) I think I saw one of his for sale on here a couple years ago for $900 used.. So... I would make the $1000 carbon tube investment. BUT.. to make them, I have to make 6061 end pieces to be woven into the tube. That would take time and engineering. Pulling out the steel sleeve from the stock trans housing was an incredible pain last night. (in order to save the casting) It was quite an eye opener.. FIRST.. they used an "OUTER" steel sleeve that is finely splined where it contacts the aluminum and extends a few inches past the housing.. They then Heat both the steel and the alum. housing up and poke/expand about six 1/2" dimples in them, compressing them together. THEN.. they insert the actual torque tube and weld up at the top of the smaller sleeve.. CRAZYNESS. So yeah.. WHAT A PAIN> to remove those sleeves without tearing up the aluminum Trans housing. and that stuff is crazy porous. Not a good cast metal at all. Weldable, but not easy either. So... i've been working on it, but am clearly at a stopping point before I fully commit to a decision. It will be a while before i get back to this...

FRporscheman

I intended it to be sarcastic but it is true too.

Hey I hate the guys that say "drop that junk box and buy a REAL porsche" just as much as everyone else, but I still like 911s a lot.

adrial

95ONE,

I wouldn't say there are zero worries about stress with a Carbon tube ...

The problem with carbon fibre is attaching it to things.

I'm not sure what you mean by "6061 end pieces woven into the tube". From what I've seen, there are 2 ways to attach metal to a carbon shaft. One, you chill the metal piece (dry ice/liquid nitrogen type chill)...shove it in the carbon and you have a ridiculous press fit. Or two, you leave it a slip fit and rely on a high quality epoxy to transmit the torque.

You generally try to avoid putting Graphite (carbon) right next to Aluminum because it can lead to corrosion issues. On a racecar that never sees much rain or salt -- no problem. But for a street driven car, it might be an issue.

You then also have to worry about the fitment of the bearings into the carbon tube ... you'll probably want a metal sleeve bonded in where the bearings rest, for robustness.

Carbon may work great if engineered properly ... but it is a lot more work than a full Aluminum torque tube.

JDS968

I know this is going to be ridiculously expensive, both in terms of materials cost AND machining, but there IS another option. What about titanium? It's very, VERY tough, and lightweight.

V2Rocket

http://www.ticotitanium.com/products...seamless-pipe/

95ONE

You can have the carbon tube manufacturer build your part into the tube when they weave it.


Agreed.. lots of work either way. more so for the carbon fiber. but once again.. You can have the carbon tubes inner diameter made to your spec's. So a 3.05 inner diameter is needed, and I would just tell them to make it that size and then you just re-use stock bearings. (cages.)