What do sub frame connectors really do...

[SN65]

I have been dying to try out that structural foam in the A pillars and roof structure for a while now. I will be interested to see how easy it is to work with and the results.

I think that the results of the struct foam addition will be mixed at best. Yes, it will make the "A" pillar itself more robust, but it will do nothing for the attachment points (where the pillar meets the cowl and roof). I believe that there is much more deflection at the joints than in the pillar itself. I think that the struct foam is more benificial when used on items that are under a twisting or bending moment than under compresion or tension.

I have also been toying with building a similar style of brace as your front shock tower brace except as a backbone on the center console. What I mean is leave the original sheetmetal there, and weld a tubular structure onto it to form a backbone from the firewall area to the backseat area. Have you considered this? I believe this will cut down on torsional deflection without intruding into the passenger compartment like a cage would. I would be interested to see how this would work.

Do you mean like a torque tube in a 3 link rear? I guess it would work if you came off the top of the firewall and followed along the trans tunnel and tied it off with a cross brace at the rear torque boxes.

But, I believe, in general, that it is better to beef up the perimiter than it is to reinforce the center.

I like the idea of the beefed up rocker panels for various reasons, the first being crash safety. A subframe connector does nothing to help you in the case of a side impact, but a beefed up rocker panel could very well minimize intrusion. It also as you have stated, ties into the structure of the body which is nice. It might be beneficial to beef the rockers up AND install subframe connectors in a car like a camaro or firebird where there is a subframe that bolts to the middle of a flat panel. Keep thinking outside the box!

Thanks for the kind words. I am taking a lot of what I see on late modle cars and applying it to the early stang chassis. Rockers on late modle cars are very stout.

Also, I have to think outside the box. I tried to get inside the box on several occasions, but no one will let me in. :-)

[SN65]

SNIP...

In your initial post you asked "what do subframe connectors do?" All I am doing is making the point that a simple connector would probably do the same job you are drafting the rockers to do.

SNIP...

Mark

Hi Mark,

I guess this thread has gottena bit off base a bit. Originally I was trying to get a few thoughts on how people thought that SFC's functioned. A lot of people I talked to thought that it was a "torsional" device. While I believed that there were some minor torsional gains, I figured that the real benifit of a SFC was in lengthening the lever arm.

Now we are talking about uni-body chassis design.

Maybe we should rename the thread to match the scope of the thread?

[jaybee]

IMO the key to success with your approach is looking for the "hinge points" in the chassis. By that I mean that beefing up the rockers will have minimal effect if the subframes aren't tied in with sturdy torque boxes. Similarly, bracing the shock towers into the firewall better won't be fully effective without providing a way to take those forces straight into the rockers because the firewall will just flex at the bottom like a hinge. Obviously you've put a lot of thought into how forces move through the chassis and you are reinforcing those force paths. No matter how they're constructed it's hard for me to imagine subframe connectors being as effective, especially in torsional loading.

[astroracer]

I wouldn't change a thing Bob... As you stated, it is all relative, and any indepth conversation HAS to branch out to include relative and pertinent data. I think this is a great thread and it has started me thinking about the Bad Ast underpinnings as well...
Anyone with any experience (or interest for that matter) in this stuff should be eating this up. I think hotroddr has some valid ideas also which are worth further thought and investigation. I know his "backbone" idea has been used extensively in older style roadrace cars and it is a valid method of tying the two "ends" together. Applying it to a later model build would be interesting.
Lots of good stuff here, thanks for the initial post...
Mark

[BonzoHansen]

Are those Herb Adams? I have a set to install and have some questions. Thanks.

http://www.alstonracing.com/

[David Pozzi]

Hi Mark,

I guess this thread has gottena bit off base a bit. Originally I was trying to get a few thoughts on how people thought that SFC's functioned. A lot of people I talked to thought that it was a "torsional" device. While I believed that there were some minor torsional gains, I figured that the real benifit of a SFC was in lengthening the lever arm.

Now we are talking about uni-body chassis design.

Maybe we should rename the thread to match the scope of the thread?

SN65,
It's your thread, so I can split the thread into two, with another one talking about chassis stiffness or rename this thread for you.

I think renaming this one is best, and a lot easier for me I don't want to accidentally mess something up trying to spit it.
David

[hotroddr]

What Im proposing with the backbone thing is basically an exoskeleton that you would weld over the existing sheetmetal. This would give the middle of the car more torsional rigidity but wouldnt be in the way because its right where your console would be anyway. If it is triangulated and tied into the roll bar near the main hoop and into the back downbars I think this would help a lot without sacrificing safety or interior space. The front portion could tie into your shock tower brace to distribute forces better. Obviously the structure would require more thought than what I sketched but this helps to illustrate my point.


The reason this would be better at resisting torsion than rockers or subframe connectors is that it places mass farther away from the plane of the floor. In other terms it has a higher moment of inertia than rockers or SFCs.

[SN65]

Here are some photos of the roll bar setup. More photos are available on our website.

[SN65]

Hey!!! Why am I getting links to the photos and not the photo itself???

What the )((@&$)((& am I doing wrong???

[JMarsa]

Are you using the insert image button in the non-quick reply form?

--JMarsa

[BRIAN]

The problem with comparing any structure to a newer car is not really accurate just because you use the foam or??? Newer vehicles are using high strength steels and I believ Volvo is using borium or some other type of high end steel in their rockers. The foam and other materials are made to be used together to create a more solid structure. You can por faom into a weak structure and I am not sure it will make it stronger?


What I get out of the Hot Rod market is guys usually do not use the vehicles actual structure to support anything besides the outer skin of the body. Problem comes in when roll cages are deleted as you now have no impact protection and a weakened outer sheetmetal.


I am building a 51 Ford and have tried to make the structure stronger without adding any cage at all. Im interested in your outcome. I kind of did the opposite as I concentrated on making the center section from the cowl to back seat area the strongest. I hid 2x3 steel in the factory rockers. I also tied the lock pillar and hinge pillar into the rockers again with hidden tubing. I then took 16 gauge sheetmetal and made channels that use the existing sheetmetal to form a square tube. I boxed the entire cowl in this manner. There is also a 1 5/8 tube running from hinge pillar through the door to the 1/4 panel. There are obvious gaps at the door but those areas were also plated and are placed at the lock area for addly support. Using the 16 gauge as a channel opens up options where square or round tubing can't go. You can box upper drip rail areas and also reinforce the floor pan wherever needed without cutting up the floor for round or square tubing.


I am no engineer and these are just my ideas to build a cool car that will be a little safer plain and simple.

[SN65]

The problem with comparing any structure to a newer car is not really accurate just because you use the foam or??? Newer vehicles are using high strength steels and I believ Volvo is using borium or some other type of high end steel in their rockers. The foam and other materials are made to be used together to create a more solid structure. You can por faom into a weak structure and I am not sure it will make it stronger?

The only comparison I can make to a late model car is torsional rigidity. I am not about to do a crach test for comparison sake. :-)

Struct foam will make any "tube" structure stronger. It fills the empty space and prevents the compressed side of the tube from collapsing or folding in on itself.

SNIP...

I am building a 51 Ford and have tried to make the structure stronger without adding any cage at all. Im interested in your outcome. I kind of did the opposite as I concentrated on making the center section from the cowl to back seat area the strongest. I hid 2x3 steel in the factory rockers. I also tied the lock pillar and hinge pillar into the rockers again with hidden tubing. I then took 16 gauge sheetmetal and made channels that use the existing sheetmetal to form a square tube. I boxed the entire cowl in this manner. There is also a 1 5/8 tube running from hinge pillar through the door to the 1/4 panel. There are obvious gaps at the door but those areas were also plated and are placed at the lock area for addly support. Using the 16 gauge as a channel opens up options where square or round tubing can't go. You can box upper drip rail areas and also reinforce the floor pan wherever needed without cutting up the floor for round or square tubing.

I am no engineer and these are just my ideas to build a cool car that will be a little safer plain and simple.

Sounds like a cool project. Got any photos?

[SN65]

Are you using the insert image button in the non-quick reply form?

--JMarsa

I have tried it a number of ways and one of them was using the incert image button.

WHen you use the button all it does is surround the "image location" with the text IMG and /IMG surrounded by brackets. I have been using the same procedure for quite a while but now, it does not work.

WTF.....

[jaybee]

Brian, I think that's the right approach for your project because it's body on frame. The cab has a minimal effect on chassis rigidity as opposed to a unibody which IS the chassis. Therefore the best contribution you can make is to keep yourself safe in case of an accident.

[Beegs]

Struct foam will make any "tube" structure stronger. It fills the empty space and prevents the compressed side of the tube from collapsing or folding in on itself.

It would seem to me the "tubes" would have to be capped off at the ends in order to "retain" the foam in event of compression. Am I wrong? In other words if you remove the cap off a tube of toothpaste and hit it, you know what happens, keep the cap on and hit it, now you have something solid. Just curious.

[Norm Peterson]

What Im proposing with the backbone thing is basically an exoskeleton that you would weld over the existing sheetmetal. This would give the middle of the car more torsional rigidity but wouldnt be in the way because its right where your console would be anyway. If it is triangulated and tied into the roll bar near the main hoop and into the back downbars I think this would help a lot without sacrificing safety or interior space. The front portion could tie into your shock tower brace to distribute forces better. Obviously the structure would require more thought than what I sketched but this helps to illustrate my point.
<snip>

What would build a lot of torsional stiffness into the tunnel itself would be to box it in along the bottom and provide enough bracing to keep the tunnel from "parallelogramming" as seen in front view. Obviously, any bottom elements would need to be removable, or at least open enough to allow access. And large enough at the back end to accommodate driveline displacements. I think that the open arrangement would have fewer problems arising from moisture trapped in crud that inevitably finds its way into the least accessible crevices.

FWIW, a solidly closed tunnel was the primary structural element in the Austin-Healy Sprite / MG Midget chassis, with much smaller sills making up the outboard structure. I think the floorpan in that chassis is continuous across the car, with the tunnel spotwelded above it (making for a somewhat larger, done-as-OE version of what Brian is doing).


Norm

[BRIAN]

I will try and get pics today. I actually always build the frame into the body making it the best of both worlds.

If memory serves me right the original cars to use that structural foam were the GM plastic bodied mini vans. Once again I do not think it really added any more crash worthy safety than a styrofoam bumper absorber does? I have the actual GM tech books somewhere on them.

Mfg's build unibody cars because they are light and cheaper to assemble. The early models are nothing like a Volvo or any other high end saftey cage vehicle built today. That is why the need to tie the front and rear frames together came from? If you look at DSE's site they have a tranny crossmember that runs laterally that really adds some stiffness to the car. I copied that approach but just used it for strength on a early F body. Was it stronger? I didn't measure anything but there were no more rattles and squeeks.

Somewhere there is a real engineer reading these posts saying that is why guys shouldn't be modifying these structures without some serious knowledge. I kind of agree and that is why I kind of shy away from the 1000hp stock bodied car builds. It is just asking for trouble. Putting a sticky 315 tires on suspension and rails that are meant to handle loads of a bias ply 215/70/14. I like your approach and that you are seeking out info to make it actually work. Like you said there is no way to really test without a boat load of money that can be recouped by building the same car over and over.


I think a lot of racers were also using hard setting seam sealers and applying them to all welded seams vs welding eveything up.

[jaybee]

Norm, what you're talking about doesn't sound that hard to me. Reinforcing the tunnel portion of the floorpan might be, I haven't worked that out in my head. To close the bottom of the tunnel you could put sheet angle structure so that the upright welds to the side of the tunnel and the horizontal portion to the floorpan. It would have captured nuts, nutserts, or nuts welded to the inside of the angle. Square tubing would attach to that. Then connect the two sides of the tunnel with an appropriately triangulated tube structure as dictated to allow drive shaft clearance.

[SN65]

Just finished the roll bar. Here are some photos. The last on is trying to show the quality of the welds. I think they came out great.

[Norm Peterson]

Norm, what you're talking about doesn't sound that hard to me. Reinforcing the tunnel portion of the floorpan might be, I haven't worked that out in my head. To close the bottom of the tunnel you could put sheet angle structure so that the upright welds to the side of the tunnel and the horizontal portion to the floorpan. It would have captured nuts, nutserts, or nuts welded to the inside of the angle. Square tubing would attach to that. Then connect the two sides of the tunnel with an appropriately triangulated tube structure as dictated to allow drive shaft clearance.

I wouldn't count on friction to keep the bottom plate or framework from shifting slightly under load (which mostly gives away the torsional stiffness). This has been done using shoulder bolts in close-tolerance holes in at least one replicar chassis, and you could probably work up a slightly different means of ensuring that there's no relative motion going on using more normal bolting practice.


Norm