Structural Reinforcement

[randywebb]

We are way off topic - it was not how to build a race car, it was how to stiffen a street car or at min., a car with no cage...

[Porschekid962]

If it makes it stiffer how can it be off topic? There are plenty of ppl running around in street cars with half cages. Now if you want to stay away from a cage completely then we can go that way too. To be totally fair a lot of the cars on this forum that we classify as a street car are in actuality far from it.

So if we want to talk about making it as stiff as possible ok. If we just want to stiffen it up a bit without a cage then lets go that route.

[randywebb]

B/c the topic was specifically on what could be done w/o going to a cage.

[Porschekid962]

So no cage, does that mean no tubing added whatsoever? Are we limiting this strictly to stitch welding and adding reinforcement plates? In that case there is plenty to do but wont pay off to its maximum without a cage or some sort of structuring to tie it all together. On a street car thats totally fine.

I always wondered if anyone had welded jack point to the underside of their cars. The 993 has a nice system. Something strong and unmistakeable maybe even paint it red would be great. No more wondering if you got things spot on when lifting the car.

I believe aside from the rear shock tower bracing the front end leaves a lot to be desired. A strut brace is nice, the little "RSR" whatever tabs that weld to the tubes and then recieve a brace are nice as well. What about reinforcing the actual area the a arm mounts to? Everyone talks about triangulating the frunt struts with a brace but as far as I know or have seen no one reinforces the front a arm mount point or tries to tie that in in someway.

I like the idea of stiffening without a cage, that way if one ever goes in it can do its job more efficiently without putting too much stress on its mounting points, you could then build a lighter and simpler cage.

So how about adding some sheet metal to the front end, linking the a arm mounts together a bit more and then into the strut towers. The way I see it if you were to break it down is the 911 has a front substructure and a rear substructure (for arguments sake) tied together via the rocker channels, center tunnel, floor and roof if you car has one. That means the majority of fore to aft bending or folding about the halfway point in the chassis are transmitted via the floor, rockers and center tunnel. If you have a roof then give yourself a point.

Without altering the interior look why not cutout the center tunnel, add some bracing that ties the torsion bar tube and rear seat structure into the front end area. Find a later style center tunnel which is taller, put some tubing inside, brace it to the inner rockers and then tie into the rear mounts of the front suspension. Toss in a cage and you should be rockin. Probably much more work than anyone wants to do on something short of an over the top track car.

For street purposes I would think a list like this would be doable.
Tie rear shock towers together (tubing, sheet, whatever you want)
Tie rear shock towers to rear longitudinals with plates.
Reinforce jack points with plates.
Reinforce front shock towers (wrap em with sheet) and toss on a brace.
Weld Tbar tube to rear seat pans.
Add sheet to engine mounts & longitudinals
Sheet to inner rocker panels & lower rear seat area


something like that

[widebody911]

So how about adding some sheet metal to the front end, linking the a arm mounts together a bit more and then into the strut towers.

I plan on doing this with tubing once I put in my fuel cell. I'd started a thread about this some time ago, but i'm too lazy to find it right now. I already went through the dash from the door jamb to the 'strut brace' and then I'll continue down to plates above the forward A-arms pickups

[randywebb]

"the front end leaves a lot to be desired."

- That makes sense to me. The rear already has a structure up high that ties into the roof. The front doesn't really do that - it ties intot he A pillars rel. low on the car, thus making what seems to be an inherently weak parallelogram. The 2nd factor is that the front suspension does the steering...
For both reasons it makes sense that tieing it all together somehow would help more than doing the rear. The only thing favoring the rear is the extra wt. back there, and the ability of the rear to put the power down (i.e. to transmit torque to the road).

But I think we need a way to measure, even if it is subjective driving impressions...

[Tyson Schmidt]

I made an X-brace that triangulated the void between the front cross-memebr and the leading edge of the floorpan, that did make a noticeable difference. It is covered by the front belly pan.

The car is not here at the shop right now, but I think I have another example that I did on a steel front cross-member that I can take pics of tomorrow, if I remember.

[Porschekid962]

Good stuff Tyson, cant wait to see. I remember you telling me ages ago about the tubes you used to tie the front struts into the center tunnel on Scruffy. Go any pics of that laying around?

[Tyson Schmidt]

Originally posted by Porschekid962
Good stuff Tyson, cant wait to see. I remember you telling me ages ago about the tubes you used to tie the front struts into the center tunnel on Scruffy. Go any pics of that laying around?

Sorry Ryder, I never took pics of it. It was before the time when I had a digital camera, and besides that, it was experimental stuff, so not very photogenic.


O.K., here is a bad photo of the steel front X-member. I'll have to take a shot of the aluminum X-meber vesion that is on the car to give some sense of purpose.

[Porschekid962]

Very cool, thats a great start. Here is what I think after seeing that. I know the bottom of the gas tank might get in the way but what about a subframe or just an X that links the crossmember to the forward suspension a arm mount point?

From that point ppl who have cages into the front trunk and pickup the strut towers can continue forward and down and instead of going to the bulkhead simply go straight above the front a arm mount point. Again the gas tank might get in the way but there are custom cells available for much dinero.

Cheers, I am off

[Tyson Schmidt]

Originally posted by Porschekid962
Very cool, thats a great start. Here is what I think after seeing that. I know the bottom of the gas tank might get in the way but what about a subframe or just an X that links the crossmember to the forward suspension a arm mount point?

From that point ppl who have cages into the front trunk and pickup the strut towers can continue forward and down and instead of going to the bulkhead simply go straight above the front a arm mount point. Again the gas tank might get in the way but there are custom cells available for much dinero.

Cheers, I am off

Couldn't hurt, but the most important spots are within the wheelbase, especially connecting suspension pick-up points. It may be difficult to get ground clearance going under the tank.

[safe]

Originally posted by Tyson Schmidt
Sorry Ryder, I never took pics of it. It was before the time when I had a digital camera, and besides that, it was experimental stuff, so not very photogenic.


O.K., here is a bad photo of the steel front X-member. I'll have to take a shot of the aluminum X-meber vesion that is on the car to give some sense of purpose.

Would this be worth doing with the supports for the aluminum crossmember that is just bolted to the crossmember?

[Tyson Schmidt]

Originally posted by safe
Would this be worth doing with the supports for the aluminum crossmember that is just bolted to the crossmember?

Yes, especially so.

The undertray for the aluminum cross member is much thicker than the early ones, and I wonder if it was designed to work as a shear panel to make up for the lost stiffness when they went from welded pieces to bolt-ons.

It's a poor design as a shear panel though, due to the stepped shaped, which is why I built the X-brace specifically for my aluminum set-up.

The steel one above was one I made to help my car make weight rules for racing. Down low in the front was a good place to add weight.

[safe]

I always thought that the supports was just there to hold the sway bar....

I need to get myself a welder and do some work
I have wished I had one for years, but it has always been to far down the wish list.

[Tyson Schmidt]

Originally posted by safe
I always thought that the supports was just there to hold the sway bar....

The supports were there long before there was an under-body swaybar. Those supports tie the front pan to the rear pan. Without them, the steering rack tunnel would get smaller under braking.

If you leave the bolts loose where they attach at the rear, you will hear the supports clanking around from the flex while driving. So it definitely moves around from chassis flex.

[Wrecked944]

Originally posted by masraum
I'll take a guess at what may add some stiffness through the middle of the car.

Take the center "tunnel" run in up really high in the cabin like in the CGT and with your newly modified really short shifter (a requirement after the previous mod) have at it.

This is a great thread. I am reviving it because I recently acquired a 1973 targa with some rust issues. The car is one step away from being a basket case, so it is a good base for "medical experiments". I figure I can't exactly make it worse, right?

Introducing Porsche vin# 9113112244 - The Charlie Brown Christmas Targa

With that in mind, I'd like to try to find a way to reinforce the targa chasis without going to a full roll cage - much like 911pcars, the original poster to this thread. So I was actually thinking of something along the lines of what masraum suggested above. If I understand it correctly, using a larger center tunnel is a bit like introducing a Lotus style "backbone chassis" to reinforce the unibody. I know John said that a backbone chassis is not a great idea for our cars and that the TVR "outriggers" were a large part of that car's stiffness. But if that is the case, then why not try a TVR style chassis as a reinforcing scheme for the targa unibody.



Using a tubular backbone, you would not need to relocate the shifter. And you could tie it in to the suspension points. The outriggers could be welded to the rocker panels.

Oh yeah, and regarding the front shock towers. I've seen a zillion pics of cars that have tubular strut braces installed. But wouldn't a piece of sheet metal welded to both shock towers as a "sheer panel" be a better solution - like the 914 design? Why didn't Porsche go that route with the 911?

[randywebb]

welding a shear panel across the trunk would reduce luggage capacity -- these used to be road cars before we got a hold of them. They did that on a few special cars, IIRC.

welding a sheer panel across there would require that the factory leave their area of expertise and get into the design of lingerie....


Tyson -- can we get more details on the X brace??

[Wrecked944]

Originally posted by randywebb
welding a sheer panel across there would require that the factory leave their area of expertise and get into the design of lingerie....

Good catch! I suppose that explains why our cars are so sexy...

[Tyson Schmidt]

Originally posted by randywebb

welding a sheer panel across there would require that the factory leave their area of expertise and get into the design of lingerie....


Tyson -- can we get more details on the X brace??

ba da bump.....tshhhh

Nice one, I got it!


Randy, I had to remove the smuggler's box lid, relocate the fresh air drain tube, cut a hole where the power brake booster is on later cars, and another one behind where the drain tube is.

Then, I reinforced the front of the center tunnel, since it's very thin, and ran two diagonals down to meet the center tunnel. They don't end up being symmetrical, since you have to tuck the left side behind the gas pedal.

That's why I never tried productionizing it, or even posting any how-to's. It's simply too ungraceful. I was simply doing it as an exercize. it gave me a lot of feedback on how to stiffen an open chassis, and demonstrated the potential handling benefits of doing so, and I'm glad I did it once, but I don't think I'd do it again unless it could be done more gracefully. I may one day work something out. probably in a boxed sheet-metal way, hidden or disguised as a center console.

[DaveE]

What about replacing the heater tubes inside the rocker panels with actual structural tubing, like roll cage tubing? That would have to add some stiffness if it could be attached front and rear to a solid structural part of the car.