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simsport · Joined: 06 Nov 2002 Posts: 573 Location: UK Warrington

Here's a thought!

Take away the original drive shaft torque tube and how much weight is saved?....100...120lbs?

Then, weld in a brace plate at front and rear of car to take rear of bellhousing for clutch on engine and end of gearbox (or bellhousing on none 'Z' boxes). Fit a center support bearing and a lightweight hollow prop shaft.

The torque tube doesnt add any shell strength and just holds the box and engine relative to each other under engine torque. By removing the heavy cast tube the car might weigh a lot less. Also the hollow tube may actually slow down a bit quicker than the standard steel shaft helping down changes.

I am interested in the alloy torque tube mentioned by members of the list but wondered if anyone has done any thinking along these lines?

Cheers
Simon
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dwak · Joined: 03 Nov 2002 Posts: 839 Location: Eastern Ontario

And that torque tube rusts like a bastard and is a disimilar metal to the things it is attached to. But I guess the aluminium would corrode.
How's the horse power to weight ratio battle going, Simsport?

dwako

endwrench · Joined: 07 Dec 2002 Posts: 1631 Location: Victor, Montana

924RACR · Posted: Wed Jul 16, 2003 9:38 pm Post subject:

I would estimate that the torque tube weighs about 80lbs tops. I can't see saving more than 30lbs doing this.
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Eturbo924 · Joined: 09 Nov 2002 Posts: 2212 Location: Londonderry NH

Plus the tube helps you in both front and rear collisions. It was designed to transmit much of the force down under the car into the opposite end that was impacted. This the trasmission would take much of the force in a frontal impact and prevent the engine from sitting in your lap and vice versa.

Eric
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simsport · Joined: 06 Nov 2002 Posts: 573 Location: UK Warrington

I can see how the tube might help in an accident but remember this isnt a road car, its a race car and so is already a little compromised in terms of door bars , padding etc.
Also I suspect the effect of the tube in protecting the driver is a little dubious. A crumple zone means dissipation of energy. If the tube transfers that neatly to the rear then fine, however I think it is most likely going to move into the shell at the midpoint as it tries to twist and I'm not sure thats too good either!

Safety apart I am sure there is more than 30lbs to save. Lets consider......
The tube weighs what, 80lbs did Lizard say. Fine. 80lbs to go at.

If you consider two 1 inch thick dural plates bent and bolted to the body, one front , one rear. 9The bolt mounts would be reinfofrced into the shell0.

All up weight of these plates plus bolts plus reinforcement...what 12lbs?

Then a hollow tube. Say 25 lbs with center bearing and mount adding say another 8lbs...total weight of system 45lbs.
Saving 35lbs...looks like lizard was about right.

Saving of 35lbs is 16kilos, thats about 18 bags of sugar in good old blighty, or the same as about 3.0 gallons of fuel....or same as 20% of an average driver...so it may be worth it for performance.

Is it worth it when we consider the gearchange quality ?
The standard shaft is rigid which is good but heavy and slow to stop rotating. This mass and its stored energy makes it hard to make quick changes, the synchros dont like it as we all know.
A prop shaft will take a little more energy to turn (I think) but will also slow down more quickly as it will have less mass than the bar , and thus help the gearchange (all a guess!).

I know its not the whole answer for the PORSCHE Z Box but if I can quote an example of a simliar layout. The alfa's use a similar design in that they have a transaxle. Guess what?...they also suffer from a poor change and poor synchro life. The answer chosen by serious racers was to lighten the gears by drilling them in the correct places. This took weight out of the system and it slowed and changed better.

So,
Yes perhaps a little less safe?...need to think about that risk,
Not that much weight saved?....well its relative, even 30-40lbs saved makes real difference in a race car, and finaly
The gearchange may be worse?......I thnik it might improve a little, anything is better than now!

All in all I think this idea could work. However I am still very much attracted to a light alloy torque tube, if it comes to light for the zf box and is not too costly then it has to be a real option. If not then I think the propshaft idea may get a run out next season!

Cheers
Simon
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78porsche924 · Posted: Thu Jul 17, 2003 1:47 pm Post subject:

It also helps the torsional rigidity of the frame. I think it would effect the handling. Also this bearing will prolly pick up crap. How many bearings are in the torque tube anyway?
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Doodle · Posted: Sat Jul 19, 2003 1:10 pm Post subject:

In the early model tubes there is 4 support bearings. In the later model tubes there is 4 support bearings plus a vibration damper. I tend to agree with 78porsche924. The Haynes (page 183 section 37 says "The drive shaft tube forms a rigid connection between the engine and the transaxle, completing the backbone around which the body is hung." This implies the structural rigidity of the car comes from the engine, driveshaft tube, transmission combination and not from the body structure as in a unibody car. You might have to do some serious gussetting in order to retain the car's structural rigidity and handling characteristics.
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simsport · Joined: 06 Nov 2002 Posts: 573 Location: UK Warrington

The tube is not connected to shell at all in fact as the engine and gearbox are mounted on rubber mounts which allow movement. In efect the tube 'floats' and hence cannot add anything to the stiffness of the shell in my view...but I could be wrong!

If the engine was mounted securely to a dural plate (same setup for the gearbox) then a two piece prop shaft could run with a single center support bearing.

The dural plates would help the shell as they will tie the engine and box to it. I still reckon this is worth a try!

Cheers
Simon
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Dave951M · Joined: 03 Feb 2003 Posts: 57 Location: NC- USA

You could try to go without a tube but- the tube serves to locate the tanny relative to the engine, to act as a tranny mount, and to allow the engine method of transmitting torque without much heavier mounting systems. The crash stuff has already been mentioned.

The stock tube weighs in at nearly 68lbs, of that, the driveshaft is about 25lbs. I've built a tube in aluminum that weighs in at just over 44lbs. That's a 24lb drop. I also set it up to be far easier to rebuild than the stock unit and, as these cars age and bearings get even harder to source, I can change the carrier design to accomodate anything available off the shelf that will fit into the tube. The tube is 6061T6, 1/4 wall. Pro Stock drag cars are made from 1/8 wall, same alloy and they generate way more torque than any of us could reasonably hope to.

My tube will fit any car that takes the flange/rear bellhousing arragement. The only differences I've found so far is the collision lugs. I'm working up one for Simon at the moment for a 931. I'll have some more info as I figure out how to do the balljoint for the shift rod.
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Paul · Posted: Thu Jul 31, 2003 1:01 pm Post subject:

It would be nice to install a late shifter and rod on a 931 snailshell, so we could eliminate the 2 rod setup. I'm planning to try it on my rusty torque tube.

Since you have already made a mount for the late shifter on your tubes, hopefully it would be possible to fabricate a new shift rod for the snailshell.

Dave951M · Joined: 03 Feb 2003 Posts: 57 Location: NC- USA

don't see why not. I don't have access to a car with the snailshell, so maybe someone can get me a drawing of what is needed.
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geddes66 · Joined: 10 May 2003 Posts: 129 Location: Bakersfield CA

Here is my 2 cents since no one has had this take yet. the torque tube also if not mainly absorbs the "lifting" torque that is the equal and opposite result of the transmission attempting to rotate the tires. If the torque tube is 4 feet long and has the engine as it's counter weight then you don't need much in the way of mounts. If you eliminate that longrigid part and just bolt the short transmission to the body (in a place not reinforced) You will have to add large and heavy mounting systems and the "lifting" torque from the tranny may still damage the body where ever you have bolted it. To figure out the torque being put to the body multiply the engine torque times the ratio of first gear then times the final drive ratio then divide by the distance from the axel of your mounts. In the case of a stock 924 that would be the engine mounts. distance reduces stress.

I hope this text makes half as much sense as the picture in my mind does.
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