Added Sheet Metal in Later Coupe bodies

[randywebb]

I thought it might be useful to start this thread for the above topic and to keep it more specific than the Structural Reinforcement thread
Structural Reinforcement

(I will inter-link the two threads).

[randywebb]

In this specific thread we are interested in things the factory did to stiffen later coupes (not targas or cabriolets, which have been posted on in the Structural Reinforcement thread - linked above).

For example, was there additional seam welding rather than just spot welding?
Did P AG add additional panels to the later coupes (we know they did this to tragas and cabs).


And 2nd, in comparative driving experiences in early vs. later coupes.

For example, rdane posted on a backdating thread
(http://forums.pelicanparts.com/porsche-911-technical-forum/324130-backedate-longhood-74-rs-look-2.html#post3032984)
that the "basic long nose shells are flexi-flyers compared to the later cars." This was based on his experiences in driving both a '72 and a '79 with the same suspension set ups (wheels, TBs, shocks and sway bars). He found that "the '79 was much more planted and solid where the '72 seemed soft and flexi." Both cars were stock coupe bodies and he drove them over the same roads and also did some track work with them both over a 4 month period. Also, the body of the '72 was rust free. Of course, it was a couple hundred lbs. lighter.

rdane then tried to find some info in Frere:
"I've been looking through Frere for the last hr and nothing jumps out at me past "10 years of development on structure, running gear and tires"

Not even sure which 10 years he is talking about, but looks like '73 to '82. "Page 169 and 170."
By the data I found most of the documented changes that would make a difference in what I could easily feel driving would be the documented info on running gear and the undocumented (at least what I could find in a quick check) "development on structure".

Interesting comments on how the welding techniques changed when they went to a fully galvanized body. Makes me wonder if they added more welding on the body panels to stiffen it up...but it is just speculation. Only thing I know they changed is the loss of th outboard battery boxes and adding the door crash reinforcements. Someone should ask Tyson and Grady the same question. Better yet ask them if they think the early cars (per '74) are more flexible than the SC and Carrera series."

Besides Tyson & Grady, we thought maybe milt and/or Darryl might know something from poking around in the sheet metal....

[rdane]

Just to be clear I was comparing a borrowed '72 that was stored at my garage with my original '79 before the major face lift.

I am curious what differences Porsche incorporated after '72 up to the 3.2 Carrera that would make such a strong impression while driving the later car.

[911pcars]

Randy,
I didn't want to go through the linked post to confirm. I don't remember if I wrote the following:

When I last spoke with Mark at Eurotek (sill plate reinforcement pieces), he provided me this information :

- Prior to 74, chassis metal is .032", thereafter, .035" (20 gauge)
- RSR used two layers of .070" on the sill plate.
- On the longitudinal pieces, .035" before '85
- After '85 (C2 and C4), went to .080" thickness

Sorry. I forgot who provided the following info., but thanks:

Restoration Design replacement panels:
Inner rockers, 0.059" or 16 gauge
Outer rocker sill, 0.046" or 18 gauge

If I did, I'll delete this so as not to be redundant

Hope this helps,
Sherwood

[Chuck Moreland]

No doubt the later tubs are stiffer and chassis changes were made. Most obvious is the extra sheet metal to support the impact bumper shocks.

Yet, the driving feel between an SC and later car vs a 73 and older car is pretty dramatic. I think many things color driver perception of stiffness. The feel of the wheel, brakes, alignment settings, tire sizes, sound level, clutch, wear level, ride quality - they all change the way we perceive the car - make it feel tight or sloppy.

[Tyson Schmidt]

Off the top of my head, there is one reinforcement between the torque tube and center tunnel at the upper corners. Little eyebrows that connect them together to brace the tube.

This started in '74.

The sheetmetal became thicker in key areas, and also the spuds for the spring plate covers were lengthened.

That's all I have off the top of my head.


BTW, '71 and older are the REALLY flimsy chassis'. '72 was the beginning of the major improvements.

[randywebb]

Sherwood - that's new - don't delete!!

Thx all - this thread is getting off to a good start. We can end it well by getting somebody to stamp out the needed pieces so shops can install them...

[rdane]

'71 and older are the REALLY flimsy chassis'. '72 was the beginning of the major improvements

Good details, thanks.

[chrisp]

I would also think that the galvanizing would have some effect. It's basically a hardshell coating that I would think should stiffen up the overall design.

It's pretty amazing that the longitudenals more than doubled in thickness. That's a lot of weight.

Also, with this evidence PCA should not allow backdating. There would be a significant performance difference between say a '72 and a back dated '85 or later.

[blue72s]

Originally posted by 911pcars

- On the longitudinal pieces, .035" before '85
- After '85 (C2 and C4), went to .080" thickness

What do you mean by 'longitudinal pieces'?

C2 and C4 didn't come out until 1990 so why do you say '85?

[911pcars]

The "longitudinal" pieces include the door sill structure and below, I believe. Maybe a more correct description would be the years '85 and later to include C2 and C4 models - this data from what was described to me.

Sherwood

[blue72s]

Originally posted by 911pcars
years '85 and later

Do you have the exact month or date of '85?

[911pcars]

Originally posted by blue72s
Do you have the exact month or date of '85?

Sorry, I don't. I'm merely passing along information given to me. There's a contact number for Eurotek in the link referred to in Randy's post.

Sherwood

[blue72s]

Which Randy's post? I can't find the link or contact number.

[911pcars]

Originally posted by blue72s
Which Randy's post? I can't find the link or contact number.

It starts here:
Structural Reinforcement

Sherwood

[Bobboloo]

In 85' the gusset at the rearward end of the outer rocker was enlarged to strengthen this corner of the chassis. Porsche has made several changes over the years to strengthen this area of the chassis like the plates that Tyson mentions.

It seems that between the weight of the over hung motor and the effect of leverage from the rear swingarms that the rear seat pan/ torsion tube area takes a lot of load.

[techweenie]

Thanks, Randy, this is my candidate for 'best tech thread of the year.'

These are things I've wanted to know.

We can also look at changes made in the 964/993/996 progression -- I'm thinking primarily of the progressive 'closing up' of the open front tub aft of the upper strut mounts. I think most of us have had experience with strut braces... I've always thought the ultimate solution would be a full bulkhead ...

[RWebb]

Thanks.

I think the thing now is to consider what changes one might want to make to an early car, and whether welding those additional panels in would make sense for various types of driving:
1. aggressive street
2. lower end track/DE
3. adv. track
4. AutoX

[911pcars]

Randy,
I might have missed this previously (out to lunch). Why two user names? Is one your alter ego or is it a good guy/bad guy scenario?

Sherwood

[burgermeister]

Keep in mind that things done to improve durability (keeping things from cracking or separating)are often different from things done to increase stiffness. Small gussets or local reinforcements are generally added to improve durability. Section changes and gage changes will increase stiffness and may (or may not) improve durability.

Many things are done for crashworthiness reasons that end up benefitting durability and stiffness as an aside - I'd bet a gage change to the longitudinals falls into that category.

Galvanized panels are usually spot-welded rather than mig-welded - keeps the zinc coating more intact. Also spot welds tend to be better for durability of thin sheet steel structures than line mig welds. Without any other knowledge of the cars, I would assume newer coupes feature more spot welding and less mig welding?

Is the main stiffness under discussion the torsional stiffness of the chassis? Having jacked up my '88 911 in the front on just 1 side, I'd say they are pretty darn stiff, especially by 1970's and 1980's standards - the short wheelbase does a lot to help. Seems it would be difficult to get noticeable improvement in torsional stiffness.

Or is it local stiffness of suspension attachments?