marcb993

Hi, does anybody have a diagram of exactly which areas were seam welded and strengthened on the 964 RS ?

964russ

I think it was all the shell welds.

The big welds, the girders and that.
You will only notice a difference when you crash, spot welds tear, seam welds tear around the weld.

If you want the cup car/race look send your car to a rally/race prep place and for around 3k it will come back 10 times stronger than porsche ever made an Rs.
Seam welded cage that runs from turret to turret with a load of monkey bars in between.

alexjc4

All the details on the body mods required to go from a stock C2 to RS are in the workshop manual in an appendix to section 5. It is pretty detailed, seven or eight distinct instructions some of which require continuous seam weld, some intermittent, some on both inside and on outside, looks like mostly around rear suspension load points. Interestingly the supporting text descriptions seem to indicate they are "for safety" rather than performance. So as russ says if you want rigidity there may be better areas to look. Anyway, I'm no expert on the RS I'm just relaying what I can read in the FWSM.

Atgani

I wonder if performance and safety got lost in translation ? as strengthening the rear suspension pick up points would have little or no bearing on safety.

alexjc4

Yeah that certainly crossed my mind, hence my caveat at the end there.

That said I not sure what kind of translation snafu would substitute those two terms.

like you say, its hard to see much added impact protection from the seams they descrobe. Perhaps the spot welds dont take sustained extreme racing type loads well enough, which over time i guess might become a safety issue...

Geoffrey

When I built my car I extensively researched the seamwelding. As mentioned, the instructions are in the body section of the 964 manuals, but in reality is limited to the suspensoin area. I seamwelded every single panel in the car and it is noticably stiffer than the factory. Also, chassis do wear out, I've driven some 996 Cups with pro race miles on them, and you can feel the chassis flex as it has been weakened.

Riccardo did a tortional study on the GT3R chassis and ended up seamwelding the entire chassis as I did mine. If I recall correctly, the FIA outlawed the seamwelding of the chassis in the class due to the improvement in lap times.

Do a search in this forum on "Racecar Project" and you can see pictures of the seamwelding I did.

marcb993

Thanks very much to all of you, I will take a look at the 964 manual and Geoffrey, I will also look up your race car project. I think I may have read about it in Excellence magazine a few years ago.

I didn't know you could seamweld every single panel in the car without causing the panels to distort, but I suppose if you take your time and do it carefully enough, why not ?

I wasn't planning on going that quite far, however, although I envy the result.

I use my car as a daily driver on less than perfect roads and as I am going with a stiffer suspension set up, I thought that perhaps by seamwelding around the suspension area I would spare the chassis some abuse from running the stiffer set up.

So the objective is more to dissipate the additional forces caused by a firmer suspension on city roads and help protect the long term longevity of the chassis, rather than trying to squeeze out an extra tenth on the circuit.

Am I nuts ?

Atgani

In theory it's a good idea, in practice to do it properly means stripping the suspension and inside trim out. The areas to be seam welded will need all traces of paint removed (and any seam sealer) then and only then can you do a top quality welding job.

This a sample of the seam welding on a shell I'm currently having prepared :

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964russ

Even that weld isnt a complete seam weld.
Ive been in a rally car that had lines of weld that run complete end to end.

IMo in a road car the difference is v.little, and not worth the effort.

evoderby

Whether worth it or not depends on largely two things:

1) Torsional stiffness of the standard shell to begin with

2) Required suspension stiffness

As an example the Lancia Integrale (8x WRC champion) bodyshell is as floppy as a cardboard box in standard road trim. Seamwelding and adding chassis braces is really worthwhile and brings the shell up to a spec comparable to more modern rally machines like the Subaru and Mitsu.

Luckily the 964's shell is much stiffer, but definately not in the 30.000 Nm / degree league of current carbon tubbed supercars. A stiff shell really let's the suspension do it's work, especially when running stiff springs which would otherwise cause massive chassis flex and uncontrolled wheel movements. This is one of the reasons why modern cars can run pretty stiff suspension and still remain comfortable (example BMW 3series M-package suspension)

Things as bodyshell cycle time indeed also come into play. I remember a German magazine once put a 150K kilometer VW passat on Matter's chassis test jig.....it had lost something in the region of 40% of its torsional stiffness compared to a factory new shell!!!

Would our 964's NEED it? For most street applications I indeed doubt. Would you notice the difference? Yes you would, especially since these shells in 20 years time have degraded to some extent....when doing total bare metal restorations I'd certainly do it since it's only little extra work. On a fully painted car it's going to be very messy!!

One more thing. Seam welding changes the crash characteristics of the shell, for this reason I've read Porsche recommends certain areas in the front bulkhead area to be left well alone.

To illustrate the effects a friend of mine working for Saab Trollhatten (Pike's Peak engine development) once told me that during crash testing new road cars they found adding a front steel strut brace caused severe injury, whereas without this device the crumple zones worked as designed and left the 'occupants' unscathed.