What do sub frame connectors really do...

[SN65]

I have been giving this a lot of thought.

And

Even though a certain amount of twist is applied to the frame rails during acceleration and cornering, I believe that the benefits of sub-frame connectors are not as much torsional (is that a real word?) but in that they extend the lever point on the sub-frames further back in the chassis.

Is this correct?

[astroracer]

I believe that the benefits of sub-frame connectors are not as much torsional (is that a real word?) but in that they extend the lever point on the sub-frames further back in the chassis.

Is this correct?

Yes, but they also improve the torsional (it is a word) resistance a little. A roll cage will improve resistance to twisting more then subframe connectors alone. In combination they work well to stiffen up the "two part" chassis...
Mark

[High Plains Mopars]

Think of it this way, get a shoe box, take the lid off and give it a torsional twist. Now put the lid back on, tape it down, and twist it again.

[silver69camaro]

Think of it this way, get a shoe box, take the lid off and give it a torsional twist. Now put the lid back on, tape it down, and twist it again.

That would be a good convertable/couple analogy...but not sure about subframe connectors. The top is adding another shear plane, which isn't really what subframe connectors do.

How about fastening two rows of popcicle sticks to the bottom?

[Mkelcy]

Think of it this way, get a shoe box, take the lid off and give it a torsional twist. Now put the lid back on, tape it down, and twist it again.
That would be a good convertable/coupe analogy...but not sure about subframe connectors. The top is adding another shear plane, which isn't really what subframe connectors do.

How about fastening two rows of popcicle sticks to the bottom?
Perhaps the correct shoe box analogy is to cut out the center 4" of the bottom of the shoe box from side to side, twist it; then tape on your popsicle sticks (likely any flavor would work) with, say, two inchs of overlap front and rear and try your twisting again.

[silver69camaro]

Cut out the center? Why would that be?

To hell with cars. I'm moving to shoeboxes and popcicle sticks!

[Nine Ball]

Just think of them stiffening the chassis and allowing the suspension to work properly. These old cars weren't meant for high HP in stock form, they have a lot of twist and flex.

Example, when I got my red '69 finished, I took it to the drag strip and ran low 11s with a lot of drama. The car was scary and felt loose, even on drag slicks.

Then I had the 6-point rollbar and Global West subframes welded in, and the car went straight as an arrow down the track with no drama. Without any changes it went 10s and launched perfectly level.

[SN65]

I think people tend to get confused with the "shoebox" annalogy.

But, that is the refference we are stuck with, so I guess I will have to live with it. :-)

Take the shoebox and glue two popsicle sticks to it. 1/3rd glued to the box and 2/3rds hanging off the front. Locate the popsickle sticks about 1/4 of the way from the edge of the box, just like a frame rail. Now take the box in one hand and push up on one popsicle stick and down on the other in a twisting motion.

What happens?

The floor of the cardboard box caves in on one side and bulges out on the other.

Now extend the sticks all the way to the back of the box and repeat. You get the same results but reduced somewhat.

Now, remove the extensions and place a stick across the floor of the box at the end of the frame rails and repeat. You get less deflection in this configuration.

In my mind, by running a brace across the floor at the end of the frame rails, you achieve the same benifits of extending the frame rails, but you also remove a considerable amount of flex from the floor.

Does this make sense?

[astroracer]

Yes it does Bob, but the "crossmember" doesn't do the same job that the connectors will. The connectors tie the car together from front to back. On a hard launch the car will want to "bend" around the weakest point in the floor. This point is at the front of the spring mounts. This bending is not controllable. It will bend differently with every launch depending on conditions, traction, engine tune , whatever. The connectors tie the spring mounts into the forward subframe which makes the floor of the car much stiffer and moves the bending point forward. This increases the effectiveness of the launch. Instead of "bending" the car in the middle at the initial launch the newfound stiffness wants to move the whole car. This reduces the lost motion incurred by the bending, quickens the 60ft times and makes the car more predictable at launch and, as Nine ball stated, much more stable at trap speed.
As an example:
Take your shoe box and cut the "doors" out of both sides. Build your popsiclestick rear frame with the front of the "frame" about where the back of the doors are. Now do your twisting. Add your crossmember and twist it again. NOW add a connector, from the front of your rear frame to the front of the box. How does that work to keep the box from drooping when you tilt it up from the back? it should work much better. The same principle applies to the short subs in the unibody cars.
Mark

[Beige]

That sounds like what was said in the first post.

[bbnova]

Anyone know where I can buy some REALLY BIG popsicle sticks? Are they good for roll cages too?

LOL! Seriously, the shoebox/pop stick analogy is pretty good.

[vanzuuk1]

I have a carbon fiber shoebox with titanium popsicles sticks.

[SN65]

We are currently modifying the unibody structure of a 65 Mustang coupe.

So far, on our test bed, without the addition of a "cage" or "sub-frame connectors" we have reduced chassis "twist" by 67%. We still have a number of mods to make to the chassis. At this point we still have not welded the floor to the rockers, tied the frame rails to the seat pans, installed the export brace, etc...

When complete (without a cage) I am expecting a 75% improvment in chassis stability. Or, if you prefer, a 75% reduction in torsional deflection. Once we add the cage, we are expecting the number to be somewhere in the 80% to 90% range.

I am still debating if we should add any type of sub frame connector. If the rest of our design is correct, I feel that we really should not need them. Also, if we did not add a cage, you would not be able to tell that we made any mods at all.

We are adding a full cage to the car, along with some other goodies, to make a run at the Maxtion Mile and possibly the Silver State Classic Challenge. Our goal is to bring the car in at under 3,000 lbs. Once we know the final weight, we can determine our HP requirements.

Well, it is time to get back to work.

OBTW, we will be showing the completed car at the Detroit Autorama. Maybe this year they will put us right up front with the big dogs. :-)

[SN65]

Bolting in the export brace brings deflection down to .319 The original deflection measurement was 1.062". That currently brings us to a 70% improvement over stock.

[High Plains Mopars]

Wow, never thought the shoe box would have sparked so much conversation.

In any case, yeah, I guess adding the top to the box is more of a convertible/coupe comparison, like silver69 pointed out. So in that case, I'd say taping the top down to the box is like adding subframe connectors. It reduces deflection. Eventhough an untapped lid will reduce movement, there is still some there. Tapping is down reduces it further.

This is why; a lot of the cars we love are built out of sheetmetal that is spot welded together. Although is may be thick sheet, it maybe strong sheet, and there are lots of spot welds in it, it is still a collection of seams and spots. These seams allow deflection. Adding subframe connectors are a quick and easy way to shore up some of the flex that is inherent with a unibody design. It goes without saying that these conenctors are most effective if they tie into the floor pan rather than just tieing front and rear sub frames together.

Now, if you are so inclined, you could fire up the welder and stitch every spot welded seam on your car. This will produce the same results in rigidity because it eliminates flex points. Although SN65 didn't mention what mods they performed to their latest project to reduce deflection, welding seams would likely produce improvments like those mentioned in the last post. But, it takes a long time and some skill to do this much work. Most guys I meet would rather slap in a set of frame connectors and go.

For another analogy, if you try to rip a new, button on shirt off your bod, does it tear down the middle of the material, or does it pop the buttons off? Those spots welds are just buttons holding your car together. ..and in most cases they are 25-40 year old buttons that have been left outside most their lives.

[David Pozzi]

I'm interested in handling performance which requires torsional rigidity. I'd like to see how much subframe connectors increase it. I think there needs to be a diagonal component to the subframe connectors to significantly help torsional rigidity. Typical subframe connectors are a good thing, but I think there is much more to be gained if a better design were developed for us open track guys. Look at how GM designed the convertable, they added a plate and structure underneath to tie both sides together. Something that could do this but farther back tying in the front spring perches would be nice, but it wouldn't leave much room for exhaust.

[High Plains Mopars]

Xing the subframes is definetly a big help. I can't provide you with numbers thoug. I can say that I have always added X braces underneath the floor pan of my track cars.

As you point out, exhaust tubing clearence is a big issue which is why I haven't tried it on any of my street cars. However, it certainly would be possible. My X braces have always been round DOM tubing. By altering the size and location where they mount into the sub-frames, or how they track along the floor pan, you can adjust how much room the bracing takes up. For example, in my Dodge Aspen, the dissimilar levels of the floor pan means any bracing starts under the floor at the front of the car and ends up on top of the floor at the rear of the car. This requires cutting into the floor pan to allow tubing to pass through. This does provide an advantage in creating a more solid struture, but makes loads more work. It also makes carpeting a bit more of a hassle and costs some rear seat leg room.

Similarly, you could create pass through ports for exhaust tubing. Look at Morrisons G-Max chassis' for an example of this. These days we also have the luxery of oval exhaust tubing. It is a bit expensive, but could be utilized to reduce exhaust height by half without compromising flow. See Spin Techs web site for oval exhaust tubing, although I'm sure you can find it other places.

[chicane67]

It also depends on material.... round tube vs. rectangular.... wall thickness and diameter.... and how its attached all have huge impacts in the mechanics.

What is more tortionally ridgid, rectangular or round ?? Start there and apply common sense.

A shoe box and pop sickle sticks may give you an elementry introduction to what is going on here, but has very little to do with the end result.

[Damn True]

I'm interested in handling performance which requires torsional rigidity. I'd like to see how much subframe connectors increase it. I think there needs to be a diagonal component to the subframe connectors to significantly help torsional rigidity. Typical subframe connectors are a good thing, but I think there is much more to be gained if a better design were developed for us open track guys. Look at how GM designed the convertable, they added a plate and structure underneath to tie both sides together. Something that could do this but farther back tying in the front spring perches would be nice, but it wouldn't leave much room for exhaust.

I think the cage, if designed properly, satsfies that no?

I have a feeling (no tech to back it up) that adding some structure between the front ends of the 1st Gen sub and something good and sturdy used at the trans x-member would diminish the lever arm effect of a stiff spring way out on the end of a subframe member.

Instead of front hoops on a cage? No. But in addition too.

[David Pozzi]

True,
A cage is the usual way road racers have beefed up unbody cars. I think Mark Donohue was one of the first guys to do it, and he stated the results were great. Cages were not done much before that due to the extra weight, only roll bars. SCCA actually restricted roll cage attachment, it had to connect to the unibody and I think only the front braces could connect directly to the sub.

The roll bar we put in my wife's 73 Camaro made it feel a bit more solid.

Front braces firewall to sub on a Camaro would help tie it in, the fenders do quite a bit too.

[SN65]

SNIP...

...SN65 didn't mention what mods they performed to their latest project to reduce deflection...
Opps, sorry...

Here is a link showing all the mods made to date.

http://sn65.com/Fire%20&%20Ice%20unibody%20reinforcement.htm

Here are some photos showing the rocker, floor pan mods

https://static1.pt-content.com/images/noimg.gif

https://static1.pt-content.com/images/noimg.gif

https://static1.pt-content.com/images/noimg.gif

Here is a photo showing the cowl, firewall, shock tower reinforcements.

https://static1.pt-content.com/images/noimg.gif

We need to add the final shock tower brace and weld the floor to the rockers before we can take our final "test". After that, we can add the cage and see just how much we gain at that point.

Also, we are working on a modified Monty Carlo bar that not only helps maintain the distance between the shock towers, but also helps reduce overall front clip deflection.

[JMarsa]

Bob, if I understand yor technique, you jacked up the car and measuredan amount of "sag" on one (opposite?) side of the car. And yoursubsequent measurements after improvemnts are reducing that amount of"sag"??

--JMarsa

[BonzoHansen]

Front braces firewall to sub on a Camaro would help tie it in, the fenders do quite a bit too.Like this, or do you need someting more substantial?
https://static1.pt-content.com/images/pt/2006/09/100_1701-1.jpg

[SN65]

What we did was support the car at all 4 suspension mounting points. We locked down 3 points and left the front drivers side float. We apply 10 PSI pressure (as read on the pnumatic lift's pressure gage) to the structure that supports the drivers side. This "pressure point" is actually 20" away from the frame rail. We then measure the amount of lift at a set point near the frame rail.

https://static1.pt-content.com/images/noimg.gif

https://static1.pt-content.com/images/noimg.gif

[6'9"Witha69]

To add something to the Xbrace idea, Hotchkis makes this for convertibles. Wonder how well it would work in other applications. It seems to be in line with the ideas presented here.

http://www.hotchkis.net/cgi-bin/EDCstore.pl?user_action=detail&catalogno=1404

[David Pozzi]

Bob,
Thanks for posting the links to your page. I really like your approach to the project.

BonzoHansen,
I'm familliar with those braces. I believe Herb Adams was the first to come up with them. The only thing I don't like about them is having to work around them. I'm wondering if there is a way to brace the sub without having tubes in the way of the engine. They also attach to the A arm bolt so you have them to deal with when aligning the car.

[Damn True]

Opps, sorry...

Here is a link showing all the mods made to date.

http://sn65.com/Fire%20&%20Ice%20unibody%20reinforcement.htm

Here are some photos showing the rocker, floor pan mods

http://sn65.com/images/Fire%20&%20Ice%20Images/06-09-27%20011.jpg

http://sn65.com/images/Fire%20&%20Ice%20Images/06-09-27%20012.jpg

http://sn65.com/images/Fire%20&%20Ice%20Images/06-09-27%20038.jpg

Here is a photo showing the cowl, firewall, shock tower reinforcements.

http://sn65.com/images/Fire%20&%20Ice%20Images/06-10-09%20027.jpg

We need to add the final shock tower brace and weld the floor to the rockers before we can take our final "test". After that, we can add the cage and see just how much we gain at that point.

Also, we are working on a modified Monty Carlo bar that not only helps maintain the distance between the shock towers, but also helps reduce overall front clip deflection.

Bob,

The stuff you've done looks nice, but all of the frontal changes leave a "dead path". Meaning they take the load from the strut tower and transmit them to the upper cowl, then the only path for that force is via the floor. It seems that distributing those loads from the cowl to both the SFC's and a cage via a-pillar bars would distribute the loads over a wider area and mitigate the bending force placed on the floor by the forces entering the upper portion of the cowl.

[BRIAN]

By adding all your reinforcement to the cowl forward and then the rear torq boxes back aren't you causing a soft spot in the center of the car. If you ever hit something the outer portions strength will crush the center section? Kind of the reverse of what most unibody mfg's due for safety?


I did a similar test on a 1st gen F body. I attached the front sub and measured movement as it was jacked from the front crossmember. The subframe connectors didn't really stop any flex from the cowl forward. Adding front cage struts just about eliminated all movement. Are you doing tests with front sheetmetal and doors attached? Just curious.


Weren't subframe connectors designned to strengthen the weak link in early unibody floors which lies between the front and rear rails. Some of the better designs have side to side ties.

[David Pozzi]

For drag racing it makes a lot of sense to more directly couple the subframe to the leaf spring front mounts. I'd say it's good for any car with a lot of power but I did discuss it with Herb Adams once and he didn't think it was a important for handling on a coupe. He did recommend the front braces he designed.

Some of the fourth gen subframe connectors have diagonal bracing.

[SN65]

Bob,

The stuff you've done looks nice, but all of the frontal changes leave a "dead path". Meaning they take the load from the strut tower and transmit them to the upper cowl, then the only path for that force is via the floor. It seems that distributing those loads from the cowl to both the SFC's and a cage via a-pillar bars would distribute the loads over a wider area and mitigate the bending force placed on the floor by the forces entering the upper portion of the cowl.
Hi DT,

My plan was to transmit all forces to the cowl and then attempt to reinforce the cowl in such a manner that all the forces are then transmitted to the rockers.

If you look at the cowl bracing, it all originates from the major firewall reinforcement and then runs to the rockers and the "A" pillar. Instead of concentrating on sub frame connectors, we are attempting to transmit as much force as we can to the rockers.

So far, we have reduced deflection by 70%. Once we are finished with the basic modifications we will test the chassis one last time and then start on the cage.

Also, we are going with a 3 link rear. It will have two lower control arms, a torque tube and a watts link. All of the rear suspension forces will be carried by the coil over’s. We have modified the cage design to reinforce the shock mounting areas.

We have two goals here. First is to see just how much deflection we can take out of the chassis without the addition of a cage. Second, is to see just how much improvement we get with the addition of a cage.

If we can achieve a 75% to 80% reduction with just the chassis mods and the cage nets us an additional 10%, then we will consider the design a success. At that point, it becomes a matter of refining the design.

[SN65]

By adding all your reinforcement to the cowl forward and then the rear torq boxes back aren't you causing a soft spot in the center of the car. If you ever hit something the outer portions strength will crush the center section? Kind of the reverse of what most unibody mfg's due for safety?


I did a similar test on a 1st gen F body. I attached the front sub and measured movement as it was jacked from the front crossmember. The subframe connectors didn't really stop any flex from the cowl forward. Adding front cage struts just about eliminated all movement. Are you doing tests with front sheetmetal and doors attached? Just curious.
Hi Brian,

We have made quite a few changes to the floor structure. We have more than doubled the strength of the rockers and also the center of the floor with the addition of modified convertible items.

Yes the center section is the weakest area of the car but, other than adding a cage (which we plan on doing) there really is not much we can do. If you have any ideas, I am open to suggestions.

Weren't subframe connectors designed to strengthen the weak link in early unibody floors which lies between the front and rear rails. Some of the better designs have side to side ties.

[SN65]

For drag racing it makes a lot of sense to more directly couple the subframe to the leaf spring front mounts. I'd say it's good for any car with a lot of power but I did discuss it with Herb Adams once and he didn't think it was a important for handling on a coupe. He did recommend the front braces he designed.

Some of the fourth gen subframe connectors have diagonal bracing.
Hi David,

We are going to see a lot of force at the front leaf spring mount (now a lower control arm mount) but those forces are going to be more horizontal than verticle. We are just going to beef up the mounting point a bit and allow the rockers to take most of the force. In addition to that, we will be locating one of the legs of the cage right on top of this area.

[Norm Peterson]

The closer that you can get the LCA axes to align with the rocker axes the less the bracket compliance will be, and the smaller the bending moments applied at the ends of the rocker structure will be . . .


Norm

[Rick Dorion]

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




Like this, or do you need someting more substantial?
https://static1.pt-content.com/images/pt/2006/09/100_1701-1.jpg

[SN65]

The closer that you can get the LCA axes to align with the rocker axes the less the bracket compliance will be, and the smaller the bending moments applied at the ends of the rocker structure will be . . .

Norm
Exactly, we have the LCA meeting the chassis near the bottom of the rocker and just under the bottom of the axle. I think the LCA will be close to horizontal, but will likely run uphill a bit from the axle to the chassis. Won't know for sure till we set the car at ride height, possition the axle and fit up the control arms.

[astroracer]

Just an observation on my part.
You have, essentially, made your outer rockers into subframe connectors. Tying everything together as you have does "just about" the same job that a set of connectors would do other then directing the stress path into a circuitous, round about, route through the rockers. As much work as you have done to beef them up could probably have been accomplished by a simple tube tying the front cradle directly rearward into the front leaf pocket. I am not saying this won't work as it will probably be fine. The point to be made is that, in getting around installing "subframe connectors", you have actually installed "subframe connectors"... Whether you realized it or not...
Just me thinking out loud... Anybody else?
Mark

[SN65]

Just an observation on my part.
You have, essentially, made your outer rockers into subframe connectors. Tying everything together as you have does "just about" the same job that a set of connectors would do other then directing the stress path into a circuitous, round about, route through the rockers. As much work as you have done to beef them up could probably have been accomplished by a simple tube tying the front cradle directly rearward into the front leaf pocket. I am not saying this won't work as it will probably be fine. The point to be made is that, in getting around installing "subframe connectors", you have actually installed "subframe connectors"... Whether you realized it or not...
Just me thinking out loud... Anybody else?
Mark
Hi Mark,

You know... This is the way I originally thought. But I came to the realization that you have to look at the entire structure when it comes to a unibody.

I look at the chassis as a whole with the center body section as the major unibody structure. The roof, "A" & "B" pillars, firewall, cowl and rockers form the major structure of the chassis. The frame rails need to tie back to this structure.

If you look at the rockers, especially in our case, they are the heaviest structural item in the entire car, and the basis of all other assemblies. Even if you added a sub-frame connector that was as structurally sound as our rockers (about a 6"x6" section), I doubt that that assembly would be as stable as ours. You would not be taking advantage of the rest of the structure. And, you would still need to tie this sub frame structure to the rest of the chassis through more than the floor pan.

[astroracer]

Hey Bob, you are exactly right of course, which is why "most" subframe connectors are tied into the roll cage at a couple of points.
Don't take me wrong here. I am not arguing your method. I think it will work just fine. 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. Of course the connectors would HAVE to be tied into your structure as you mentioned and would probably require just as much work as rebuilding the rockers to make them work as hard.
Mark

[Damn True]

Let's take a second to draw a distinction between a subframe connector that bolts to the front and rear and one that welds into the front and rear AND is welded into the floorpan between the two.

Bob's setup clearly emulates the latter and should by far exceed the former.

[hotroddr]

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 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.

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!

[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 :rolleyes: 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.
https://static1.pt-content.com/images/noimg.gif

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.

https://static1.pt-content.com/images/noimg.gif

https://static1.pt-content.com/images/noimg.gif

[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.

https://static1.pt-content.com/images/noimg.gif

https://static1.pt-content.com/images/noimg.gif

https://static1.pt-content.com/images/noimg.gif

[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

[jaybee]

I see your point. What if the structure closing the bottom of the tunnel has sturdy tabs on it so that it fits snugly up into the tunnel and cross-bolts horizontally as well as vertically?

[SN65]

Just got back from SEMA and an extended vacation in Aruba. Had a great time at both, but, I am happy to say, it is now time to get back to business. If we are going to get both of these cars ready for the Detroit Autorama, we are going to have to get our butt's in gear. :-)

In regard to the original subject of this thread, I just spent about an hour talking to Chris over at Maximum Motorsports. He told me that they did some before and after testing on Fox body sub-frame connectors.

And the results are....

Sub-frame connectors have little to no effect on improving torsional stability. They do help improve “beam” deflection of the frame rails, but do nothing to reduce torsional deflection or "twist".

There you go. Sub frame connectors will help stiffen up and help reduce "sag" or "bounce" in the beam direction, but do little, if anything, to reduce chassis twist.

[David Pozzi]

Just got back from SEMA and an extended vacation in Aruba. Had a great time at both, but, I am happy to say, it is now time to get back to business. If we are going to get both of these cars ready for the Detroit Autorama, we are going to have to get our butt's in gear. :-)

In regard to the original subject of this thread, I just spent about an hour talking to Chris over at Maximum Motorsports. He told me that they did some before and after testing on Fox body sub-frame connectors.

And the results are....

Sub-frame connectors have little to no effect on improving torsional stability. They do help improve “beam” deflection of the frame rails, but do nothing to reduce torsional deflection or "twist".

There you go. Sub frame connectors will help stiffen up and help reduce "sag" or "bounce" in the beam direction, but do little, if anything, to reduce chassis twist.

Thanks, It's as I suspected.

I remember the Herb Adams "Silverbird" Trans Am race car, - it had a long panel underneath that closed in the trans tunnel. I see Alston Chassisworks has an underbody brace system for first gen Camaros that is for torsional stiffening. Too bad we have to have things like driveshafts and exhaust systems underneath the car...
David

[SN65]

New update at the site

http://sn65.com/Fire%20&%20Ice%20unibody%20reinforcement.htm

Check out the fuel door we are currently evaluating.

With that said, it is time for the suspension gurus to chime in and help with the front end geometry.

Here are our issues....

We are going with a strut front suspension. We intend to use the early Mustang lower control arm and the front strut.

When we set the suspension at ride height, we have about 1" of suspension travel before the lower control arm buries itself into the frame rail.

Is this enough? I don't think so.

To gain more suspension travel we can modify the lower control arm and front strut or we can go with a 2" drop fox body spindle and strut.

If we alter the lower control arm assemblies by sectioning and "bending" we will end up with about a 1" rise from the control arm mounting position to the ball joint pivot point. If we go with the 2" drop spindle we will end up with about a 1" drop from the control arm pivot point to the ball joint pivot.

I am thinking that it will be better to go with the 2" drop. I can always relocate the control arm mounting point down a bit if the goal is to end up with a true horizontal plane from the inner pivot point to the center line of the ball joint.

Any input would be greatly appreciated.

[astroracer]

Modifying the LCA is probably your best bet Bob. Leave the inner and outer pivot points where they are and build a new arm to connect the dots.
https://static1.pt-content.com/images/pt/2006/11/BobsLCAmarkedupvi-1.jpg
Dropping the inner pivot isn't a good idea because then you start getting into steering problems. Bumpsteer, ackerman, that kind of stuff. If you can build a new arm to hit the old points and clear your frame you will be heading in the right direction.
Figure out how much travel you have and then add about a 1/2" to that for clearance.
Mark

[SN65]

This weekend we finished up all the chassis mods. Just some grinding and sanding and we should be ready to drop her back on the frame rack for the final torsion test.

Here is a link to the latest photos.

http://sn65.com/Fire%20&%20Ice%20unibody%20reinforcement.htm

It will be interesting to see what the final numbers come in at. I am guessing that we will have reduced torsional deflection by somewhere in the 80 to 90% range. Not to bad for a car without a cage.

[SN65]

Hummm....

We just performed our final torsional test and the numbers have not changed from the last test.

Hummmm.......

We are currently at 70% reduction in torsional deflection. I would have guessed that all the welding and the last few mods would have netted us some gain, but evidently not.

However....

We did cut the lips off the rear quarter panel / wheel opening in preparation for the fender flares. Right now, the quarter is not attached to the outer wheel housing. And, the quarter draws tight on the side under pressure and loosens up on the side under compression.

This must be throwing off the numbers. I guess we will have to weld the quarters back up before we can finish the test.

It is funny how little things can have profound effects.

[Steve1968LS2]

Would the subframe connectors (ala DSE) help more with torsional/twist rigidity more than ones that hang below the floor?

I would think that having them through the floor would help with body twist to some degree.

[jaybee]

I think you'll find those wheel housings to be pretty important once you weld them back together and retest.

[SN65]

Would the subframe connectors (ala DSE) help more with torsional/twist rigidity more than ones that hang below the floor?

I would think that having them through the floor would help with body twist to some degree.
Hi Steve,

From what I have seen in our testing and from conversations with the engineers at Maximum Motorsports, I would have to say that all subframe connectors will help in regard to beam deflection, but none will have much impact on torsional deflection.

I would guess that the DSE items would be a step up from the hang below the floor variety, but without any comparative testing, it is difficult to say just how much of an improvement you would see in the real world.

I really like the subframe connector design by Maximum Motorsports. If you look at their design, they tie the middle of the SFC to the seat pans with a cross brace. This stiffens up the structure by reducing the unsupported length of the SFC by 50%.

It is interesting to me that no one publishes any test data on their structural modifications. Everyone and their brother (or sister) makes a subframe connector, but no one publishes any data on what the actual improvements may, or may not, be.

When dealing with a group of car fanatics who will pay thousands and thousands of dollars to improve performance in any way shape or form, you would think that testing and publishing the data on chassis modifications would be a no brainer. We pick just about every component in our cars car based on some kind of quantifiable performance improvement, but chassis mods are picked based on recommendations and "empirical" data.

Has anyone out there seen any type of published data on chassis modifications?

[James OLC]

...they tie the middle of the SFC to the seat pans with a cross brace. This stiffens up the structure by reducing the unsupported length of the SFC by 50%.



Would that not suggest that the DSE style SFC, which is welded to the floor along their entire perimeter, would provide superior support as there is no unsupported portion of the SFC? It seems to me that the benefit of the cross braced connector would be the actual cross brace itself being perpendicular to the SFC.

Just an observation

James

[Steve1968LS2]

Would that not suggest that the DSE style SFC, which is welded to the floor along their entire perimeter, would provide superior support as there is no unsupported portion of the SFC? It seems to me that the benefit of the cross braced connector would be the actual cross brace itself being perpendicular to the SFC.

Just an observation

James

I happen to be doing a story on installing a set of DSE SFCs.. I talked to Kyle yesterday and mentioned this thread. He said their test showed that their SFCs do help with torsional twist. He also said they will have data on this available soon.

I let him know about this discussion, so hopefully he will chime in.

The cross brace deal is nice but hard to package with stock stuff like a driveshaft and exhaust. Most of us are not building race cars so how stiff do we need it?

[the camtender]

If rollcage is tied into dse sfc,it will also aid in torsional deflection?

[SN65]

What we are finding (on the early Mustang) is that the structure rear of the drivers seat is much more stable than the area in front of it.

The above revalation probably comes as no surprise to anybody.

I question how much any SFC will help with torsional stability or "twist". They will help quite a bit with beam deflection. It will be interesting to see, and I look forward to, their before and after test results.

[SN65]

If rollcage is tied into dse sfc,it will also aid in torsional deflection?
Well..... I would say yes and no. it depends on the location and configuration of the brace.

I try to picture the load path in my minds eye. If you push up on one corner, where is the metel going to move and how can we modify the structure so that the loads all transmit to the major unibody structure. To me these areas are the frame rails, the rockers, the floor, the cowl firewall, the roof, etc...

You will also note that I am doing nothing to the structure in front of the shock towers and nothing behind the rear axle. If I were using lief springs I would be looking at picking up the rear spring mount, but we arn't so I am basically ignoring that area. I think it is important, for safety issues, to keep modifications in between the front and rear suspension. Maintain those crumple zones, such as they are, as much as possible.

Hope this makes sense.

[SN65]

Well... Things are moving along.

We have the fender flares roughed out. We won't be able to do the final fit until we test fit the 3 link rear end.

https://static1.pt-content.com/images/noimg.gif

Also we have finished boxing the motor mount reinforcements.

https://static1.pt-content.com/images/noimg.gif

[SN65]

We have been working hard on areas of the car you will never see.

Here is the cowl before we started....

https://static1.pt-content.com/images/noimg.gif

Here is the completed cowl....

https://static1.pt-content.com/images/noimg.gif

We just have to weld up all the holes we are not going to use and we will be sending it off to the media blaster.

[71dusterdan]

just my .02 and i am just spitballin here. on the duster we cut 2x3 tube into the floorpan and opened up the rear frame rails, inserting the tubes and then welding everything solid. so mine come up through the floor. and then we jacked up the car at the front leaf spring mount and it lifted the entire side of the car up, with eyeball measureable difference in Sag(twist) we then did the xv motorsports front outer wheelhouse mod ie tying in the firewall to the shock tower and inner fender structure. we then jacked the car up again at the same location. it actually lifted 3/4 of the car, the only tire on the ground was the front tire diagonal from the jacking point. sorry there is no scientific data or measurements but you could see the difference. i still intend to triangulate my subframe connectors out to the rockers. it should be fairly stiff once she hits the track. thanks for letting me share my truly unscientific and unsupported observations. Dan:wedgie:

[MonzaRacer]

OK you guy are the shiznit on racing and performance but get back to what your working with.
Production Uni-body cars.
Unit Body contruction. The only thing connecting the front to the back are rockerboxes, floor pans and the roof.
Now while you guys all go in different ways to achieve the same thing the one thing I learned when I went through and extened performance driving/tuning/building class was that you HAVE to stiffen a box to make it handle,,,, period.
Every car we worked on and drove(teams had different cars) there were 6 people to teams and we had a laundry list of parts to install ,,,kind of like the Forsa Motorsport Challenge. But we made changes as we talked them through and learned.
The 68 Camaro we drove was a very low miles car with a stout 355 and a 4 speed(it was in the 80s) and I thought it handled real good and actually laid down almost as good as the instructor but then he told me things as we went that made sense. We first put in the bolt in subframe connectors, then the roll bars. Then as I was in tech school at the time we talked alignments and we really got a lot of insite into that too. Then new springs and shocks. A better set of bushings frot the front end then the trick of redrilling(or moving the bolt) the spring cups to raise the front of the spring.
We also ran 1/4 mile times too to see how thae cars bettered ot flatered.
We only lost times once in straight line as we went to a custome set of "road race headers" the Vette guys had a ball and made good work of a 78 Vette (we got second by .10 of a second in final competition. AND the Fox Mustang(79 ) was right behind us by .15 sec.
When we started the car was all floppy and sloppy andwhen we jcaked it up to swap tires we found the whole side of car would come up after tieing it to gether.
Dont forget you still have a small drag race taking off or your doing doughnuts.
Torsional rigidity is as important as the flex of the car bending on take off.
Too much rigidity will allow the car to actually lift the inside tire off the ground,,and on soem cars this makes them fast and loose as when you lift a inside tire is isnt giving traction nor control.
BUT now adays we can adjust the chassis much better to allow for it so I would rather have a stiff frame and adjust the bolt ons.AND the stiffer car is safer in my opinion at least for a racing.
I built a set of connectors for a guy who had as car (I forget what it was) but the connectors ran next to the trans tunnel and we ran out riggers to the rockers but we made cutouts for the exhaust and other items, heck we even ran the pbrake cable through hole in the connectors we wleded pipe into to to close it up. the car was a completely different car.
He had only made basic changes in the chassis and when I tied it together and his mkid plate and motor plate tied to it the car was fast and handled so good he drove it for 2 yrs with old 4 cyl before building a bigger engine. The connectors were still 2x3 x.125 steel but the tubes going out made Xs underneath. and were welded to the floor and rockers completely and I welded up some panels that were only spot welded.
It was some forien car (european ) but was a limp wimp before and he was told it would never run good.
also the subframe connectors will keep high powered Uni-body car from cracking where body panels are joined like T-Top TAs and such.
Good luck to all.

[Norm Peterson]

Buried in the above post is a pretty good illustration of the effectiveness of "X" bracing in stiffening a shallow box against torsional loading. Short of honeycombing the whole volume, it's about as good as you can get. There's actually a simple derivation in Blodgett's "Design of Welded Structures" book (Lincoln Arc Welding, IIRC) of a simplified formula that you could use to estimate how much improvement you get, which you might be able to use to optimize the details a bit.

When you build in a lot of extra torsional stiffness, you do have to re-visit the springs and sta-bar package, as the stiffer chassis will transfer more lateral load transfer to the one end than the original flexi-flyer did. In the Pro-Touring context, that usually reads "less understeer / more oversteer".

Norm

[SN65]

I have been studying a bit of data covering the structural analisys of a NASCAR chassis.

A lot of it applies to unibody construction.

For example. The major chassis members are...

The rockers and central cross brace (on a unibody the rockers and the seat pan that runs from rocker to rocker) are the major lower structural members.

They tie from the rockers to the frame rails with structural tube. (Torque boxes on a unibody)

Then they have the frame rails front and back with a cross brace at the front and rear suspension mounting points. That is it for the chassis.

The major torsional members in order of sensitivity to torsional loads translated from NASCAR to unibody are

1 the roof structure that runs from the "A" pillars at the windshield to the "B" pillars behind the drivers door.

2 The strut towers and any reinforcement that runs from the tower to the firewall at the "A" pillar.

3 The "A" pillars themselves.

4 The front frame rails from the firewall to the core support.

5 The rockers and the torque box structure.

6 The structure at the top of the windshield.

7 the structure at the botom of the windshield or cowl area.

8 the frame rail extension that runs from the firewall to the seat pan structure.

Addressing these 8 areas is where the best bang for your buck will be in reducing torsional deflection.

I find it interesting that, under torsional loads, the area under the greatest stress is the roof structure at the edge of the roof just over the side windows.

Of course if the "A" pillars and other areas of the car are not correctly reinforced none of the loads will transfer to the roof, etc, etc, etc...

We have just about finished all of our modifications and we have reduced torsional deflection to just over 1/8".

Wayne is sanding and primeing now, but as soon as the chassis is in primer I will post some more shots.

[David Pozzi]

Bob,
Have you calculated torsional rigidity in foot lbs per degree?
That would be more informative.
David

[SN65]

Bob,
Have you calculated torsional rigidity in foot lbs per degree?
That would be more informative.
David
Thanks David, When we set up for our final test, we will generate that info for you.

I am guessing that lbs/degree will generate some type of curve. But, in order to make the data acurate, we are going to have to use a dial indicator to take the measurment. We are down to about 1/4" deflection at this point. I am hopeing for a little less when we are complete.

[David Pozzi]

I cheat and use a digital angle finder with two decimal place accuracy. I had one with .1 deg accuracy but with me standing on a piece of tube across the front of the car, the car only deflected .3 deg, so any improvements were going to show 1/3rd, to 3/4 change.

A dial indicator in different positions along the chassis length is good. I also thought of using a laser level along the chassis, but it would take more calculations to convert it to degrees.
David

[SN65]

I guess if we were smart, we would have used the laser measuring system.

We will have to take that route next time we do this. It will not only give us deflection at the frame rail but also key points along the chassis.

[SN65]

Here are come AutoCAD drawings I worked up showing the changes we have made and the cage we are working up. The cage is still a work in progress.

https://static1.pt-content.com/images/noimg.gif

https://static1.pt-content.com/images/noimg.gif

Green is the original structure.

Red shows the additions

Yellow are the mechanical modifications.

The suspension (front and rear) is all custom. The torque arm is designed to handle over 1,000 ft lbs of torque.

More to come...

[David Pozzi]

Just installed the DSE weld-in subframe connectors in our 73 Camaro. I haven't driven it yet, but my wife has run one Autocross, and two open track days. She says she can't tell the difference seat of the pants. No change in handling or feel. We'd already installed front "G" braces which made a huge difference. GW solid subframe mounts were installed long ago.
Just our experience, we are glad we did it for the long run. Hopefully the roof cracking will not get worse.
David

[saunacrank]

So what kind of shoes will be in this so called box we speak of.......

[JEFFTATE]

So what kind of shoes will be in this so called box we speak of.......

Carbon Fiber .

[SN65]

We have been moving along and now have the cage installed.

For giggles, we put it on the frame rack and performed a quick torsional stability test...

We supported the chassis at the 4 suspension mounting points (the rear frame rails just behind the rear axle and the front frame rails at the CL of the front wheel)and let them all float. We started to lift the chassis at the front left mounting point and measured the deflection when the left rear moved off its perch.

Total deflection was at .06"

[jaybee]

'Total deflection was at .06" '

That's impressive!

[SN65]

Well, we really won't know what the real "improvement" is until we test our completed car against a totally stock 65 coupe.

The installation of the motor and the shock tower brace, etc... will have an impact on the final numbers.

Also, we weill set the car up for a standard test to see how it really compares against cars with a known lbs/degree number.

When complete we are guessing that the car will weigh in at about 2,700 to 2,800 lbs....

Bob

[47lt1]

OK, i got my button up shirt, popsicle sticks, shoebox, glue and scissors, but now I'm really confused.

I did however notice that adding subframe connectors to my car changed the seat feel a lot! acceleration, braking and handling, even jacking up one side to work on something, it seems much more rigid.

[mrn2obelvedere]

Just out of curiosity, has anyone played around with using the engine block as a structural member? They do this with motorcycle engines. If you properly engineered your engine mounting scheme then it seems that it would be possible to substantially stiffen up the front end.

[JRouche]

Just out of curiosity, has anyone played around with using the engine block as a structural member? They do this with motorcycle engines. If you properly engineered your engine mounting scheme then it seems that it would be possible to substantially stiffen up the front end.

Using the engine block as a structural member has been around for some time. The issue that should be looked at is the overall stress that will be placed on the tabs and ears of the block. If it is a production case that was never designed for the purpose of suspension loads along with the ability to support its own stresses there is a certain failure.

I am amazed at some of the apparent loads being placed on a Formula One engine and gear box. I have a nice article showing some of the configurations on those cars. Its a large PDF file. I could email it to you, I think its kinda large.

But what I see is some deep engineering to use the case of the engine and gear box to take the suspension loads. And these cars are very light. The drive train amounts to a larger percentage of the overall weight of the car compared to a street car. Same with the high tech motorcycles today. The drive train is a major portion of the entire weight of the vehicle.

A street car has so much more weight that is not the drive train.

The production blocks just are not meant for it. They are a small part of the weight equation compared to a F1 car or a race ready street bike.

A V8 is just not designed to withstand the force of 750Lbs springs, there is no place on the case that can withstand that force.. Better to focus on the frame and advancing its abilities I think... JR

[mrn2obelvedere]

I can't find anything there to argue with. Clearly production based blocks aren't designed to have suspension loads directly applied to them. What if you use a creative set of front and rear engine plates in conjunction with other frame members? With a bit of creative triangulation, you could create a stiffer front end, with the engine effectively being a zero load member. The rear plate could really tie in to the fire wall, and give a nice distributed loading to other parts of the unit body.

I'm just bouncing ideas around here. As you will come to see, I am constantly thinking of different stuff. Sometimes I think of good ideas, other time not so much.

[Bjkadron]

I can't find anything there to argue with. Clearly production based blocks aren't designed to have suspension loads directly applied to them. What if you use a creative set of front and rear engine plates in conjunction with other frame members? With a bit of creative triangulation, you could create a stiffer front end, with the engine effectively being a zero load member. The rear plate could really tie in to the fire wall, and give a nice distributed loading to other parts of the unit body.

I'm just bouncing ideas around here. As you will come to see, I am constantly thinking of different stuff. Sometimes I think of good ideas, other time not so much.

I think most race cars already do that.?