Sub Frame connector conundrum

[4mulaSvaliant]

OK, so as I dig around here looking at build threads and car shows I see something that troubles me.
I'm sure this has been discussed before but I have yet to see it.

It may be worth some discussion and may confuse a few and may help few others.

The issue I have noticed is the 2 basic types of Sub frame connectors people are building into their cars.

1. The piece / pieces of tube NOT welded to the floor but running parallel to the floor.

2. Laser cut to match the floor or tube cut into the floor. (either way the point is that it is welded to the floor pan)


So here is the issue I have with this.

The weak point in our little A bodies when it comes to the chassis, is twist between the front and rear frame rails. SO.... The units that are not welded to the floor pan seemingly do nothing more than keep the front and rear rails from separating (stretching the car front to back).
There isn't an issue with these cars when it comes to that.

On the other hand the units that are welded to the floor pan have basically caused "triangulated" structure between the front rail, rear rail and the floor pans. Strengthening the body significantly.

Look at it this way..... Are the existing rails welded to the floor pan? Of course.

Think about the construction of a bridge..... If you just put 4 rails together, 2 on top and 2 on bottom and tied them together only ant the ends, they would sag, twist, and in general move independently. You have to tie them all together (by triangulation as is typical). Its just not enough to run more structure parallel to each other.

I'm sure there are varying opinions on this but I think its important to realize you may very well be adding extra weight rather than strengthening the integrity of you little A body.

Let the opinions begin!!! LOL :toothy7:

 

[LXguy]

I did mine like this:

http://www.bigblockdart.com/techpages/connectors.shtml

Thicker stiffer metal goes back to the spring perch/box area (dont want those chassis points moving around if the suspension is going to do its job), welds directly to the front torsion bar crossmember.

Not like the basically worthless Mopar subframes, and not using the wafer thin floorpan for "strength" like the laser cut deals. I can move the floorpan around by hand.

Yes, the car is stiffer. Doors close better, even when its up on stands. Drives better like the suspension is absorbing the bumps rather than body flex, and fewer squeaks and rattles too. (Credit to Dave Phillips for the time, lift, fab and welding.)

My install:

See how far they go back?

Beefy!

UNless you get reaallyy low, no one ever sees them

After:

 

[Bad Sport]

I did mine the same as LX. The difference is night and day when cruising down the road.

I guess to use your analogy a little different would be to take 2 pieces of flat wood about 3 inches long and glue a strip of tin foil in between them. Grab each piece of wood and twist in opposite directions and see how much flex you have. Now glue 2 pieces of wood under the tin foil to the wood and try again, see a difference?

 

[Rice Nuker]

Your logic is not accurate in my opinion. Have you tried to twist a box tube? I have not. I can only imagine what it would be like. There are 4 parallel walls all intersecting at a right angle w/o seams. Now you connect two of these box tubes from the rear frame rails to the front and you you have 8 walls and 8 90 degree seamless intersections. The torsional rigidity is proportional to the strength of the box tubing. The separate box tubing running parallel to the floor board yields 2 more walls for strength than the units which are laser cut and welded to the floor. The box tubing is considerably thicker. Using your similar logic one could perceive that the advantage in tying the frame connectors to the floor is mainly not in torsional strength but in the bow and bend of the mid section on an axis across the middle of the floor boards. This is also moot since the roof structure, the floor structure and a box tube sub frame connector all combat bow as well.

In summation, I would use the non scientific modeling process to say that the walls of box tube sub frame connectors are thicker, seamlessly intersected at 90 degrees and also increase the number of walls by 2, so would be much stronger. There is no possible way to prove which ones are better w/o measuring torque applied to different sections of the body while the body is on a jig w/ measurement equipment all over it.

.

 

[rjsjea]

I dont know about scientific modeling or bridge construction, but speaking from first-hand experience the "parallel" (as stated) bars make a substantial difference in feel of an Abody car.

I bet in a side by side, same car, same suspension the fully welded in connectors would perform better.

Mine have been changed now, although the car has not been on the road since.

My worthless take....

 

[1968FormulaS340]

Anything is better than nothing. Even the bolt in mopar connectors make a huge difference.

Im not going to allow myself to over think this.

 

[rapom65]

What Rice Nuker said! Actually I've done them through the floors, attached to the floors or under the floors but always used at a minimum 2x3 .120 wall tube or even 1 5/8 roll cage tubing welded side by side. The rigidity was so good I couldn't tell the difference. The real issue is installing them. The floor pans, unless new, usually have suffered from some rusting over time making them even thinner to try to weld heavier gauge metal to. Plus this is all done overhead or on your back, unless your one of the "blessed" with a rotisserie. Your probably right that it is structurally stronger attached to the floor but i think it would take measuring equipment to show it. Is that extra rigidity worth the effort? I just built a set of underfloor connectors for my Duster. When I install them I'm going to weld a panel on top of my connectors where they're up against the rear floor board and try automotive panel adhesive as a way to connect the two (welded on the ends of course---I know someone would have asked). I'll let you know how it works.

 

[RustyRatRod]

Yeah. Anything is better than nuffin. I agree though that tying the floorpans in makes more sense. The factory did it.

 

[Old Tired Rebel]

Subscribed

 

[Dart_Doctor]

Yeah. Anything is better than nuffin. I agree though that tying the floorpans in makes more sense. The factory did it.

x2

 

[crackedback]

If you aren't building a cup, FC, TF, or other big HP, limited flex chassis, don't overthink this is my suggestion. You are already working within an already designed box so to speak.

Put a pair of connectors on that you like and find aesthetically pleasing and move on.

As mentioned anything of reasonable size is better than nothing.

 

[twofosho]

This whole issue was addressed here a couple of days ago in another post, apparently not successfully.

As for differences between the various types and installation techniques, the real issue is corner to corner torsional rigidity.

Attach the front and rear subframes to a box girder structure (rectangular tube connector) and you end up with what is effectively a full frame independent of the passenger compartment box. Weld that connector continuously to the floor of that passenger box and you produce a far more rigid structure because you greatly increase the ability of the floor to resist distortion and are able to utilize the passenger compartment as a structural component (that six sided box thing again). Tie your added in connectors to the sill boxes that run between the wheelhouses under the doors with torque boxes and you increase it further. Triangulate the two smaller boxes (engine box and trunk) the front and rear suspensions attach to with additional bracing to prevent their distortion and you have just about a rigid a framework as you can get to keep the suspension attachment points in alignment short of installing a tubular space frame (read cage).

 

[Old Tired Rebel]

This whole issue was addressed here a couple of days ago in another post, apparently not successfully.

As for differences between the various types and installation techniques, the real issue is corner to corner torsional rigidity.

Attach the front and rear subframes to a box girder structure (rectangular tube connector) and you end up with what is effectively a full frame independent of the passenger compartment box. Weld that connector continuously to the floor of that passenger box and you produce a far more rigid structure because you greatly increase the ability of the floor to resist distortion and are able to utilize the passenger compartment as a structural component (that six sided box thing again). Tie your added in connectors to the sill boxes that run between the wheelhouses under the doors with torque boxes and you increase it further. Triangulate the two smaller boxes (engine box and trunk) the front and rear suspensions attach to with additional bracing to prevent their distortion and you have just about a rigid a framework as you can get to keep the suspension attachment points in alignment short of installing a tubular space frame (read cage).

Ok can you draw it out so I can understand a little better?

 

[Rice Nuker]

The only thing for sure is, the stiffer the metal used, the more of it and the more points it is attached to will proportionally increase the rigidity. Other than that, only someone with testing equipment and a scientific method would be able to tell us the facts.

 

[fastnos]

OK, so as I dig around here looking at build threads and car shows I see something that troubles me.
I'm sure this has been discussed before but I have yet to see it.

It may be worth some discussion and may confuse a few and may help few others.

The issue I have noticed is the 2 basic types of Sub frame connectors people are building into their cars.

1. The piece / pieces of tube NOT welded to the floor but running parallel to the floor.

2. Laser cut to match the floor or tube cut into the floor. (either way the point is that it is welded to the floor pan)


So here is the issue I have with this.

The weak point in our little A bodies when it comes to the chassis, is twist between the front and rear frame rails. SO.... The units that are not welded to the floor pan seemingly do nothing more than keep the front and rear rails from separating (stretching the car front to back).
There isn't an issue with these cars when it comes to that.

On the other hand the units that are welded to the floor pan have basically caused "triangulated" structure between the front rail, rear rail and the floor pans. Strengthening the body significantly.

Look at it this way..... Are the existing rails welded to the floor pan? Of course.

Think about the construction of a bridge..... If you just put 4 rails together, 2 on top and 2 on bottom and tied them together only ant the ends, they would sag, twist, and in general move independently. You have to tie them all together (by triangulation as is typical). Its just not enough to run more structure parallel to each other.

I'm sure there are varying opinions on this but I think its important to realize you may very well be adding extra weight rather than strengthening the integrity of you little A body.

Let the opinions begin!!! LOL :toothy7:

===========================================
I guess, I'd like the car to feel solid and hook up without twisting, creating stress cracks, and popping out the windows. Almost all cars I've owned I've never had a problem spinning the tires, just hooking up! I do like the solid ride that all frame connectors provide. But in my case Playing on the street mostly) I really don't plan on stressing it to a limit to where I'd worry about it. If I did, I'd also buy a roll cage and such...then start breaking even more parts then I do now.
But, like I said "I just want to drive a fun car.":love4:

 

[Revhendo]

This whole issue was addressed here a couple of days ago in another post, apparently not successfully.

As for differences between the various types and installation techniques, the real issue is corner to corner torsional rigidity.

Attach the front and rear subframes to a box girder structure (rectangular tube connector) and you end up with what is effectively a full frame independent of the passenger compartment box. Weld that connector continuously to the floor of that passenger box and you produce a far more rigid structure because you greatly increase the ability of the floor to resist distortion and are able to utilize the passenger compartment as a structural component (that six sided box thing again). Tie your added in connectors to the sill boxes that run between the wheelhouses under the doors with torque boxes and you increase it further. Triangulate the two smaller boxes (engine box and trunk) the front and rear suspensions attach to with additional bracing to prevent their distortion and you have just about a rigid a framework as you can get to keep the suspension attachment points in alignment short of installing a tubular space frame (read cage).

I'm entirely on board with what you are saying. So this is for discussion purposes only. Is there a point of diminishing returns of where the weight of the added braces overcomes the benefit?

 

[fastnos]

OK, so as I dig around here looking at build threads and car shows I see something that troubles me.
I'm sure this has been discussed before but I have yet to see it.

It may be worth some discussion and may confuse a few and may help few others.

The issue I have noticed is the 2 basic types of Sub frame connectors people are building into their cars.

1. The piece / pieces of tube NOT welded to the floor but running parallel to the floor.

2. Laser cut to match the floor or tube cut into the floor. (either way the point is that it is welded to the floor pan)


So here is the issue I have with this.

The weak point in our little A bodies when it comes to the chassis, is twist between the front and rear frame rails. SO.... The units that are not welded to the floor pan seemingly do nothing more than keep the front and rear rails from separating (stretching the car front to back).
There isn't an issue with these cars when it comes to that.

On the other hand the units that are welded to the floor pan have basically caused "triangulated" structure between the front rail, rear rail and the floor pans. Strengthening the body significantly.

Look at it this way..... Are the existing rails welded to the floor pan? Of course.

Think about the construction of a bridge..... If you just put 4 rails together, 2 on top and 2 on bottom and tied them together only ant the ends, they would sag, twist, and in general move independently. You have to tie them all together (by triangulation as is typical). Its just not enough to run more structure parallel to each other.

I'm sure there are varying opinions on this but I think its important to realize you may very well be adding extra weight rather than strengthening the integrity of you little A body.

Let the opinions begin!!! LOL :toothy7:

===========================================
I guess, I'd like the car to feel solid and hook up without twisting, creating stress cracks, and popping out the windows. Almost all cars I've owned I've never had a problem spinning the tires, just hooking up! I do like the solid ride that all frame connectors provide. But in my case, I really don't plan on stressing it to a limit to where I'd worry about it. If I did, I'd also buy a roll cage and such... But, like I said "I just want to drive a fun car.":love4:

Its all good!

 

[Bad Sport]

But in my case, I really don't plan on stressing it to a limit to where I'd worry about it. If I did, I'd also buy a roll cage and such... But, like I said "I just want to drive a fun car.

Think of it this way, the car is 38 years old it's already stressed. Frame connectors will help the car last for years to come.

 

[abodyjoe]

Talk about trying to re invent the wheel.

Bottom line is either type of connector will help stiffen the car. If you want max stiffness then stick a full cage in the *****.

Man some of you guys really like to over think things.

 

[Mopar Al]

I built these for my car, Demon34071, and a couple others. These ar 1/8" plate. Ground to match he floor. They are verry strong. And they look as if they were there from day 1. In my opinion asthetics is also verry important.

 

[Old Tired Rebel]

I built these for my car, Demon34071, and a couple others. These ar 1/8" plate. Ground to match he floor. They are verry strong. And they look as if they were there from day 1. In my opinion asthetics is also verry important.

I like those very nice.

 

[Revhendo]

Talk about trying to re invent the wheel.

Bottom line is either type of connector will help stiffen the car. If you want max stiffness then stick a full cage in the *****.

Man some of you guys really like to over think things.

Sez the guy with the full RMS suspension....:toothy7:

 

[abodyjoe]

Sez the guy with the full RMS suspension....:toothy7:

and how is that over thinking anything? my frame is tied using the directions on BBD

 

[longarm]

I built these for my car, Demon34071, and a couple others. These ar 1/8" plate. Ground to match he floor. They are verry strong. And they look as if they were there from day 1. In my opinion asthetics is also verry important.

Very nice!
Just curious.
How does the water get out?

 

[toolmanmike]

Just curious.
How does the water get out?

You should drill some holes.

Nice looking ties. Like the ones that US Cartool makes. Both styles are very strong and a noticeable improvement over no ties I'm sure. The tubular ties are easy to build and relatively inexpensive. The boxed ties are inexpensive too but more time consuming to fit and finish. Also, at least the seats and carpet must be removed because of the heat build-up on the inside of the floor pans. And yes some holes should be drilled to let the water out. A spray of undercoating or rustproofing inside the channels would be a good idea too. Have any of you guys with the tube style welded them in without removing the carpet?