Subframe connectors, which way should we
#901
07/30/03 02:28 PM
07/30/03 02:28 PM
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ZIPPY
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OK there are a couple different ways the subrame connectors can be done (with "realative ease") on the 69 B body/GTX in the sig pic. We can go 2x2 and have Todd weld them to the subrames only, or 2x3 and run them to the floor where it drops down into the back seat footwell area. I have seen them done both ways, and either one looks good to me. Which is the stronger of the two? Does the 2x3+ welding to the floorpan add very much strength? Gotta say I am not really worried about originality, even though it is a "real" GTX I want to do it as best I can. If that means cutting the floor, the sawzall is ready On the other hand, if the extra 1" isn't going to add anything, why bother doing it that way? Not being an engineer I have no idea which is better so please vote for your preference and feel free to post why you think it's better. Thanks.
Rich H.
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Re: Subframe connectors, which way should we
[Re: ZIPPY]
#902
07/30/03 02:56 PM
07/30/03 02:56 PM
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ZIPPY
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For future roll bar installation, wouldn't the 2x3 coming through the floor be better? That way the main hoop could run right through the frame connector, instead of sitting on a plate. Wouldn't it be stronger that way? Help?
Rich H.
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Re: Subframe connectors, which way should we
[Re: ZIPPY]
#903
07/30/03 03:01 PM
07/30/03 03:01 PM
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Anonymous
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Hey Zip, I know mine is an ugly A body, but you can check them out Friday night. I bought them from Mancini, but don't remember the cost. Maybe you can get an idea anyway.
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Re: Subframe connectors, which way should we
#904
07/30/03 03:07 PM
07/30/03 03:07 PM
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Zippy, the section modulus (SM) of 2 x 3 steel tubing will be 50% stronger than 2 x 2 providing the wall is the same thickness. The (RBM)resistant bending moment will be significantly improved with 2 x 3 as well. That deals with length x strength. Hope that helps.
Gene
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Re: Subframe connectors, which way should we
[Re: AndyF]
#907
07/30/03 04:26 PM
07/30/03 04:26 PM
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69CHARGERMD
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Rich, I did the exact same thing rbdodge' did,,,have 2x3 with it cut/sectioned in the back and plates up front,,,no floor cutting required... You can see it on Friday if we all get together... Todd Lamothe (bubba's) brother did the welding...wow, what a differene in the car. DOUG
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Re: Subframe connectors, which way should we
[Re: 69CHARGERMD]
#909
07/30/03 05:15 PM
07/30/03 05:15 PM
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M_D
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I would use 3"x2" in 14 gauge (.083"), it is about 2.67 lbs. per foot. To compare weight, 2"x2" 11 gauge (.120") is 3.07 lbs. per foot. In this application, the lighter wall with the extra 1" of depth will more than make up the strength compared to the heavier wall but smaller tube. Welding it in or to the floor ties everything together much more, in that case I would be tempted to use 3”x1 ½” 14 gauge.
This goes against popular opinion, but I’ll say it anyhow. Tying the rear and front frame sections together will do a minimal amount of good to solve twisting, compared to a roll cage or even a 6 point bar with a couple of diagonals thrown in. I’m not saying it isn’t worthwhile, but it just doesn’t provide the torsional strength needed.
If you use a piece of plywood to represent a flimsy unibody, and nailed 2x4’s on it to represent the front and rear cross members and frame rails, it will be quite flexible. If you connect the two ends in the middle it stiffens it better to act as a bridge or a beam, but you would notice the resistance to twisting is not improved a huge amount. Two parallel frame members don’t resist twisting well, a cage or roll bar adds depth in multiple directions, and will add much more strength.
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Re: Subframe connectors, which way should we
[Re: mopardad]
#910
07/30/03 05:27 PM
07/30/03 05:27 PM
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OK mopardad, I got ya. Outriggers. If that's the way to do it then there's no good reason to use 2x2 then. So that's out. I like the article at http://www.bigblockdart.com/connectors/connectors.htm and it is helpful, but other than overlapping it they don't explain exactly how the 3" wide connector is fit to the roughly 2" wide rear frame rail. What did they do, heat with a torch and pound on it? Smash it with C clamps or a vise? Just weld the heck out of it? Add more pieces to narrow that part? It doesn't say. From what little I understand about such things, it looks to me like if it were facing the other way (2" horizontal, 3" vertical) the sectioned back end of the connector will fit better over the frame rail, but will be somewhat less convienient to install. I don't know anything about this stuff, and never claimed anyone has to run them through the floor, I am saying that I don't mind doing it IF it gives a worthwhile improvement in strength. Looks like the silent majority is voting for 2x3 through the floor in the back and that's the way I'm leaning towards right now. Is it worth doing that way?
Rich H.
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Re: Subframe connectors, which way should we
[Re: ZIPPY]
#911
07/30/03 05:36 PM
07/30/03 05:36 PM
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ZIPPY
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Quote:
I would use 3"x2" in 14 gauge (.083"), it is about 2.67 lbs. per foot. To compare weight, 2"x2" 11 gauge (.120") is 3.07 lbs. per foot. In this application, the lighter wall with the extra 1" of depth will more than make up the strength compared to the heavier wall but smaller tube. Welding it in or to the floor ties everything together much more, in that case I would be tempted to use 3”x1 ½” 14 gauge.
This goes against popular opinion, but I’ll say it anyhow. Tying the rear and front frame sections together will do a minimal amount of good to solve twisting, compared to a roll cage or even a 6 point bar with a couple of diagonals thrown in. I’m not saying it isn’t worthwhile, but it just doesn’t provide the torsional strength needed.
If you use a piece of plywood to represent a flimsy unibody, and nailed 2x4’s on it to represent the front and rear cross members and frame rails, it will be quite flexible. If you connect the two ends in the middle it stiffens it better to act as a bridge or a beam, but you would notice the resistance to twisting is not improved a huge amount. Two parallel frame members don’t resist twisting well, a cage or roll bar adds depth in multiple directions, and will add much more strength.
Thx Mike. the frame rails are about 2" wide, so I was figuring that would fit the easiest over them, so it looks like 14 gauge 2x3 is what I need to get.
I'm definitely planning on some kind of roll bar, just won't be able to swing the dough for it this year. But now that you put it that way, it makes sense that it probably would help even more than the frame ties.
Rich H.
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Re: Subframe connectors, which way should we
[Re: ZIPPY]
#915
07/30/03 08:46 PM
07/30/03 08:46 PM
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Molloy
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Someone asked ealier about the tubing thickness on 2x2" box subframes, and my reply was:
Here's the way I look at it, and as always, I could be full of it...
Obviously the OEM frame material is a lot less than .120 wall (1/8"), so that begs the question, why use anything THICKER than the existing frame? Well, the frame sections are a lot taller, AND they are tied into the floors/fenders, so they are "borrowing" load-bearing capacity from adjacent structures. That's the beauty of unitized construction. In contrast, the subframe connector is mostly on its own. It's tied into the rear floor for ~1 foot, and then it's just hanging out there. In that case, it helps to have it a little thicker. May want to look into tying it into your seat mounts that come off the rocker panel. Pretty easy to do.
I used 2x3x1/8" on my Charger and I'm currently installing 2x2x1/8" on my 71 RR.
If the car is going to see much track time, I'd go with 2x3" tubing, and with the 14 guage (thinner) material like M D and Andy recommended.
I'm going with 2x2 11 guage on my 71RR because 1) it's a street car and 2) I don't want the connectors to be visible in the front seat area. Too bad my pic hosting service dropped me (moparpages) or I'd post a bunch of pics.
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Re: Subframe connectors, which way should we
[Re: 3404]
#918
07/30/03 09:40 PM
07/30/03 09:40 PM
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ZIPPY
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Sure seems stronger to run them through the floor.
OK guys I'll shop for 2x3 tomorrow then.
Thanks!
Rich H.
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