83 Sc Chassis stiffening?

[Old H2S]

Some back ground..
I am Old Fart, I have done this before on many cars. Over Kill is my middle name.

My new to me 83SC has 300k miles on it and has had 2 major impacts to it. The first in the drivers side front fender that was repaired but the car is out of true on the diagonal with the front main cross bar 6mm back on the driver side causing miss alignment on both door closing. The second hit was a snap over steer impacting the drivers rear wheel.
I will pull the engine to get the frame aligned.
The big question is, this unibody car is soft, and flexible still after repair, what are the best ways to firm it up without getting too much NVH ?
I usually make up custom sub frame connectors..and stitch weld the spot welded panels, build roll bars, shock mount reinforcements. Then when you add all the handling upgrades you are "down the rabbit hole" and have an upgraded brick.
What are your opinions?

[AlKidd]

Shock tower braces are quick and easy for side to side.

[Flat6pac]

Realize, the car is built not square
That’s why with larger wheels in the front, you have to roll the left fender
On the rear, the wheel fills the quarter panel differently and occasionally the wheel rubs the inside.
Bruce

[Tyson Schmidt]

The 911 is technically a “unibody”, but not in the sense that an old domestic car is. The rockers are far more substantial and are continuous from the rear engine mounts all the way to the front kick panels.

So no need for subframe connectors like in say, an early mustang.

In coupes, there is a break between the rockers and the front longitudinals, where there is basically just an inner fender well wall connecting them. This was sort of “torque-boxed” in the Targas and Cabriolets however.
So you could box this are in for some added strength and stiffness.

Rear shock tower reinforcement helps, as well as front strut tower brace with a diagonal. (3-point)

[Old H2S]

This car came from LA with receipts from well known shops and the the usual crushed in lift points in all 4 corners. I have already made a custom cross bar in the front that attaches at the front bolts of the LCA to lift the front wheels with a jack.
I might weld in some plates at the corners for lift points for when the car is at the shop..after it gets pulled out.

[Tyson Schmidt]

Originally Posted by Old H2S

This car came from LA with receipts from well known shops and the the usual crushed in lift points in all 4 corners. I have already made a custom cross bar in the front that attaches at the front bolts of the LCA to lift the front wheels with a jack.
I might weld in some plates at the corners for lift points for when the car is at the shop..after it gets pulled out.

The factory finally added lift points to the late Carreras. You should copy those for shop lift purposes.

[Mr. Merk]

Originally Posted by Flat6pac

Realize, the car is built not square
That’s why with larger wheels in the front, you have to roll the left fender
On the rear, the wheel fills the quarter panel differently and occasionally the wheel rubs the inside.
Bruce

Good to know. I am running 8's in front and had to roll the left front fender, but didn't have to touch the right side. I thought it was just my car!

[wjdunham]

Originally Posted by Mr. Merk

Good to know. I am running 8's in front and had to roll the left front fender, but didn't have to touch the right side. I thought it was just my car!

Yes, that is very interesting. On every air-cooled car I've owned it's always the left side rubbing with 7" 205/50/16 tires. Never really thought about it or realized that it was only that side until now.

Bill

[Old H2S]

[911pcars]

Huh? Wheel well rubbing solutions have little bearing on chassis stiffness. Unless coil-overs are replacing torsion bars, I'm not sure adding reinforcement there is a primary need, although every little bit helps. Add a roll cage for ultimate chassis rigidity.



I started a chassis reinforcement thread years ago that addressed mainly earlier 911s. Maybe worth a re-read. As the structure matured, the factory increased metal thickness, used high-strength alloy steel, added layers, and eventually employed CAD design and structural analysis software, etc. to increase chassis rigidity.

http://forums.pelicanparts.com/porsche-911-technical-forum/259557-structural-reinforcement.html

Sherwood

[Old H2S]

Sorry for the blown up pics?
Sherwood thank you, I need a cigarette after reading that, thanks for keeping it on point over the years that thread ran.
So on my front cross bar jack point I could improve with adding some more weld in points to the back bolts.
Make up a crossbar X brace for the front aluminum torsion mount crossbar.

[911pcars]

Yes, that thread was lengthy. I think at the tail end, someone went off on a tangent with their personal car build.

I like the square channel spanning your front torsion bar mounts. Is that trailer hitch size metal? Good idea on many levels.

- An ideal lift and/or support area for jacks and jack stands
- Adds some collision resistance to incursions from animals, ladders, curbing/parking lot wheel stops and random road obstacles.
- Add'l strength for the bulkhead/trunk structure
- Another "rub" surface when ride height doesn't clear

Sherwood

[onboost]

Originally Posted by Old H2S

Some back ground..
My new to me 83SC has 300k miles on it and has had 2 major impacts to it. The first in the drivers side front fender that was repaired but the car is out of true on the diagonal with the front main cross bar 6mm back on the driver side causing miss alignment on both door closing.

The second hit was a snap over steer impacting the drivers rear wheel.
I will pull the engine to get the frame aligned.

The big question is, this unibody car is soft, and flexible still after repair, what are the best ways to firm it up without getting too much NVH ?

The first thing you need to do is find someone with a Celette w/proper attachments. Just getting it mounted will tell you where the tub is out of align.

We've seen 911s with over 100k mis, no hits at all, but have been tracked (not as full blown racers, but consistent DE cars) and they have been flexed and needed to be pulled and strengthened. Clearly the tub you describe needs to be checked...

I would then seam-weld the side rails in the trunk, maybe add a front strut tower brace, and sway bar reinforcement plates if it has the thru the body bar in front.

In the rear, you should check the torsion tube for cracks at both ends, and also check the 4 bolts bosses where the torsion bar cover mounts.. they have hairline cracks sometimes.. You can also create a gusset to tie the torsion bar tube to the chassis in the upper area of the trans tunnel

You can plate t strengthen this area too. Then of course there is the shock towers in the engine compartment, and you can plate the area where the rails form a corner on each side heated towards the shock tower.

Get it on a Celette first and see what you have.

Good luck!

[Flojo]

to stiffen the car just add the ST & RS(R) reinforcements:
- welded strut bar at front between towers (RS) and add a full cross (RSR)
- plate inside front wheel well at lower arch above roll bar (l & r)
- corner plates in engine bay where crossbar and longitude meet (l & r)

[Mr. Merk]

Originally Posted by Flojo

to stiffen the car just add the ST & RS(R) reinforcements:
- welded strut bar at front between towers (RS) and add a full cross (RSR)
- plate inside front wheel well at lower arch above roll bar (l & r)
- corner plates in engine bay where crossbar and longitude meet (l & r)

Do you have pictures of the wheel well reinforcements?

[Old H2S]

The box tube I used is 1 1/2" square with .125 wall.

[911pcars]

Originally Posted by Old H2S

The box tube I used is 1 1/2" square with .125 wall.

Thanks for sharing.

S