Structural Reinforcement

[Elombard]

David put your jack under the front a arm suspension mount and lift. That chassis twists like a pretzel.

I have heard from several people that the font ends are "soft" as compared to 964s??? I wonder what the difference is in the 964 to make it stiffer. Seems like the strut towers would not make that much difference?

If you cut a big hole in each end of the gas tank support in the trunk over the front a arm mounting spot. Made a "mount" that would attaach using the same bolts (as the a arm) and ran a x bar to your shock tower. In other words make an 'X' like the factory race roll cages but bolt in instead of weld in.

I have wondered if this would noticeably stiffen thigs up. Seems like you might need to tie the shock towers back to the fire wall/fram rails?? to really get a benefit.

[davidppp]

Hello elombard.

The front end is indeed a weak part.

The reason is generally rust inside the boxed sections where the crossmember mounts, and over and behind the steering rack.

But a glance at the design around this and the footwell region will suggest three or four places where stiffeningl sections will help..ideally welded on boxing or top-hat, but doubling plates do help too..

Kind regards
David

[Elombard]

Hmm

David Is there any way to see in those areas to see how rusty it is? I just did my front pan and I dont want any more rust!!!

[davidppp]

Yes, its quite easy to drill for a borescope..

But nearly as good is to use a hammer and a little experince.

There is an unmistakable differnce between the solid noise of thick metal and that of rsuty bits..

Howver, to be honest, if you have the front end stripped already it is no more than a days work each side to open the boxes, and reinforce the crossmember mounts, and rreweld

if you are serious about stiffening this is a good place to start IMHO..

It is unuasual indeed to find any pre 76 car without significant rust in there..and the design and execution was not great anyway..

Kind regards
David

[blue72s]

That list is very informative. I'm amazed with Bugatti Veyron , 44,000 Ft.lbs/dg...

Does the 911 Carrera 4 also mean a C2? If so, why not buy a C2 tub and backdate it? 50% stiffer already, and further stiffen it with more steel.

[Bill Verburg]

Does the 911 Carrera 4 also mean a C2?

The 993 C4 tub is a little stiffer than a 993 C2. That was one of several reasons that the factory chose to build the RS on a C4 tub

[AtomicDog]

blue72S wrote:

I'm amazed with Bugatti Veyron , 44,000 Ft.lbs/dg...

It's carbon fiber - built in an era where engineers know how to really take advantage of CF's tensile strength. Look at the Young's modulus of CF compared to steel. Then, if you're interested, look at boron vs. CF. High stress areas of the space shuttle's CF structure are reinforced with boron. It makes CF look like overcooked pasta.

Chris

[davidppp]

Hello again.

Just thought some might be interested in knowing a bit more about "modulus" in this context.

Carbon fibre has a very similar Young's modulus to steel in fact.

Note, I'm talking approximations here..I know there are different CF grades..

But is much less dense, hence maybe 10 times lighter for the same stiffness.

It is interesting to note that pretty much all our usual metals have almost the same stiffness to density ratio.

It is commonly mistaken that high grade steels are stiffer..ie higher modulus...they are not.. but they are less ductile once the elastic limit is breached.

Kind regards
David

[AtomicDog]

davidppp,

I confess I picked a ringer for the CF - Hexcel UHM 12K,

density: 1.87 g/cc
UTS: 541,000 psi
MoE: 63,800 ksi

Looking through some of the medium and high alloy steels, AISI 1137 quenched/tempered and others,

density: 7.87 g/cc
UTS: 128,000 psi (tool steels will approach 300K)
MoE: 29,000 ksi (as above, tool steels are around 30K)

I searched MatWeb for ANY metals with a UTS >500,000 psi and MoE >50,000 ksi. The server timed out with no result.

Where the steels shine is in fatigue stress and fracture toughness. I wouldn't build a pressure vessel out of anything else...

Chris

[davidppp]

Agreed...CF and steel are '"comparable in modulus!

Do those stiffness numbers refer to anisotropic finished laminate?


what is also interesting is the energy absorbtion in failure..not too much ductility in CF!

PS I love CF for boats..


Kind regards
David

[AtomicDog]

David,

Touche. I'm sure those numbers are not for a laminated structure.

This has got to be where the Bugatti engineers spent most of their time, no doubt. The vacuum bagging and curing rigs must have been impressive.

Cored or solid for the hulls? What is the latest and greatest on the core materials front? I haven't looked into composite boat construction in over a decade...

Chris

[blue72s]

Thanks all.

Originally posted by Bill Verburg
The 993 C4 tub is a little stiffer than a 993 C2. That was one of several reasons that the factory chose to build the RS on a C4 tub

Was the 964 RS (Euro) also built on a C4 tub?

Hard question I know but what is the rigidity rating of:

964 C2
964 C4
964 RS (seam welded)

993 C2
993 C4
993 RS (seam welded)

TIA

[Wil Ferch]

I'm re-entering this thread and excuse me if this has come up in discussion....but I am still leery of the 2000 number quoted here..although Mark Donahue is credited for the quote..and his credentials were impeccable...

However, this question : Is there a common "test" set-up for this ? Meaning:.... where is the load applied and how is the chassis braced to counter-act to the applied load? Is it at the point where the wheels intersect the body, and if so , is the other-axle's location used a reference point, with that area blocked or braced ? ( This, in my mind ...would mimic the real-world better than some other locations where the force may be applied).

Is it therefore possible, we're quoting different numbers and the point where the applied force is applied is different...thereby making comparisons invalid ??? Example: the longer the "chassis"..and the further apart the two locations are ( applied force vs. braced area)..the "weaker" the body will appear to be, since it will twist more.

- Wil

[randywebb]

"steels shine [] in fatigue stress and fracture toughness..."

- Absolutely & bears repeating. It might be useful to consider what can be done to 1. stiffen the unit body and 2. make various parts out of other materials to save wt. (e.g. what about the engine carrier? could it be Ti or some other lighter metal? it weighs a lot and is way out back...)

[davidppp]

FWIW, I'd not be too urprised if the bare 911 shell measures at 2000 lb/ft per degree.

Much less than modern cars sure, but pretty respectable all the same.

And the weight of the old 911 is relatively low, which reduces the spring srtiffness needed.
I daresay a moderately well-prepared shell with a very good large tube cage will more than double 2000....

A rule of thumb used to be stiffness of chassis three times the suspension stiffness in roll at the stiffer end.


Ps I wonder about solid laminated epoxy- glassfibre for the rear engine mount..solid mounts of course..very resilient, lighter, and as strong as steel of the same thickness.


Kind regards
David

[blue72s]

I just googled and found this:

The Type 996, introduced as a 1999 model, was a major leap for Porsche. For the first time in the evolution of the 911 the car shared no major mechanical components with its predecessor. An all-new bodyshell offered a dramatic 45% increase in torsional rigidity over the 993.

So, if a 996 coupe has a torsional rigidity of 19,861 Ft.lbs/degree (as stated on Sherwood'd list), then a 993 coupe calculates as 13,700 Ft.lbs/degree.

[911pcars]

It's unclear in some of the references if the specs were determined with or without the engine/drivetrain in place. In some, it's just bare chassis figures (perhaps from FEA calculations).

With or without the gas tank, I think the front end is a weak point in terms of torsional rigidity. That might be why the factory and others added cross-bracing to the trunk, not just between the strut towers.

Sherwood

[911pcars]

Something like this, what ELombard suggests in his previous post:

[randywebb]

Exactly.

But where am I going to load the fertilizer bags with that in the way?

[blue72s]

Unless the suspension points are fastened to the engine/drivetrain (as some race cars are), I don't know if makes any difference whether the engine/drivetrain is in place. 'Torsional rigidity' means the relationship between the front and the rear. The less twisting between the two during cornering the better.