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Re: Frame connectors
[Re: Tech Instructor]
#2093266
06/17/16 12:09 AM
06/17/16 12:09 AM
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Joined: Dec 2005
Posts: 11,558
Fulton County, PA
CMcAllister
Mr. Helpful
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Mr. Helpful
Joined: Dec 2005
Posts: 11,558
Fulton County, PA
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Nope, as long as it's large enough. Many higher end back-half cars (think Super Stock), and 25.whatever cars are done all in round tubing that's integrated into the floor pan. The rectangular tubing has flat sides that make it easier to section and weld into the floor, set cage bars on top of it without having to notch, etc.
If the results don't match the theory, change the theory.
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Re: Frame connectors
[Re: CMcAllister]
#2093316
06/17/16 02:01 AM
06/17/16 02:01 AM
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Joined: Dec 2013
Posts: 4,672
Wichita
GY3
master
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master
Joined: Dec 2013
Posts: 4,672
Wichita
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2X2 square tubing slid into the rear framerail works well and doesn't interfere with most stock floorpans.
'63 Dodge 330
11.19 @ 121 mph
Pump gas, n/a, through the mufflers on street tires with 3.54's. 3,600 lbs.
10.01 @ 133mph with a 250 shot of nitrous an a splash of race gas. 1.36 60 ft. 3,700 lbs.
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Re: Frame connectors
[Re: Tech Instructor]
#2093336
06/17/16 02:35 AM
06/17/16 02:35 AM
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Joined: Dec 2003
Posts: 22,696
Bitopia
jcc
If you can't dazzle em with diamonds..
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If you can't dazzle em with diamonds..
Joined: Dec 2003
Posts: 22,696
Bitopia
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Any reason not to use round DOM tubing? Yes, if you felt "beam strength" was more of an issue then "torsional strength", round tubing vs square or rectangular?, would not be your first choice. And "DOM" increased cost in this application, has little upside, IMO.
Reality check, that half the population is smarter then 50% of the people and it's a constantly contested fact.
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Re: Frame connectors
[Re: Tech Instructor]
#2093502
06/17/16 01:50 PM
06/17/16 01:50 PM
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Joined: Dec 2005
Posts: 11,558
Fulton County, PA
CMcAllister
Mr. Helpful
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Mr. Helpful
Joined: Dec 2005
Posts: 11,558
Fulton County, PA
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I suppose I should have said "depends" on what else is going on; full chassis, no roll bar or somewhere in between. 1-3/4" 1020 DOM tubing is pretty stout. But if the only thing going in is a set of frame ties, then the added strength and cross section of 2x3 sectioned into the front of the rear frame rail (assuming it's a typical Chrysler product) and the floor and butted up against the rear of the torsion bar crossmember would be a stronger set up. The 2x3 has a much larger cross section and there's just more area to join the floor pan and tubing together. Even with a simple 6 or 8 point, it will be stronger overall. With 2x2, the advantage is less. Keep in mind, it doesn't matter how strong the tie is - if you have it welded in only at the ends of the tie it's better than nothing, but it will flex the sheet metal at the weld before it flexes the stronger tie. Sectioning it into the floor will give the maximum benefit.
If the results don't match the theory, change the theory.
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Re: Frame connectors
[Re: dogdays]
#2093528
06/17/16 02:58 PM
06/17/16 02:58 PM
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Joined: Jan 2004
Posts: 4,566
Motor City
6PKRTSE
master
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master
Joined: Jan 2004
Posts: 4,566
Motor City
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I have round tube under my Challenger tied in with the cage.
Last edited by 6PKRTSE; 06/17/16 02:59 PM.
1963 Belvedere 440 Max Wedge Tribute
1970 Charger R/T S.E. 440 Six Pack
1970 Challenger R/T, 528 Hemi
1970 Charger 500 S.E. 440 4 BBL
1970 Plymouth Road Runner 383
1974 Chrysler New Yorker 440
1996 2500 RAM 488 V-10 4X4
2004 3500 Dually Cummins 4x4
2012 Challenger R/T Classic.
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Re: Frame connectors
[Re: dogdays]
#2093647
06/17/16 07:12 PM
06/17/16 07:12 PM
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Joined: Dec 2003
Posts: 22,696
Bitopia
jcc
If you can't dazzle em with diamonds..
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If you can't dazzle em with diamonds..
Joined: Dec 2003
Posts: 22,696
Bitopia
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From a design standpoint, metal that is farther out from the neutral axis works harder. As a 2x2 square tube has more material farther away from the axis it is stronger in either torsion or bending. This is a Strengths of Materials, learned from Mr. Ron Apanian back in the day. Anyone else reading this take Strengths from Apanian?
As far as stiffness goes, any steel has approximately the same spring constant or modulus of elasticity as any other. So 1018 and 4340 start bending at exactly the same stress. The difference comes when the bend becomes permanent or yields. The 4340 has a much higher yield strength than 1018.
If welding was perfect then welded tubing would be less expensive, but that long seam seems to have the occasional weak spot. Of course, using a safety factor of 4 or so should cut the stress so that the weld will not fail. Just don't ask me to calculate maximum stress or safety factor for a frame connector!
R. The issue above not mentioned here or by me in my earlier reply, frame connectors have multiple stresses imparted on them, and to the op's question, tension would care less what shape the member, and compression forces would be best with round, and as large as physically allowable. Not sure that a 2x2 square tube compares favorably to a 2" round tube from a strictly torsional standpoint, comparing equal weight per ft materials, although it has greater material farther from the neutral axis you mentioned. Correct me if I am mistaken. Your comment on "welded tubing", is indeterminate to me, most of our typical tubing is welded, including DOM. All of this has been covered on moparts ad infinitum. What has never been proven or even narrowed down, is exactly what forces are at play with the frame connectors, and in what applications are they notably different.
Reality check, that half the population is smarter then 50% of the people and it's a constantly contested fact.
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Re: Frame connectors
[Re: Tech Instructor]
#2093814
06/18/16 02:25 AM
06/18/16 02:25 AM
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Joined: Oct 2007
Posts: 4,206
New York
polyspheric
master
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master
Joined: Oct 2007
Posts: 4,206
New York
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The greatest load in racking (angular twisting of the chassis by application of power, in which the axle planes are no longer parallel) is bending in the vertical plane. More height increases stiffness, which is why rectangular frame connectors are taller than they are wide. Welding through the floor makes it a structural member, otherwise it's a big tin playing card. Compare the frame rails of 1/2 ton and 1 ton trucks - the height difference is huge. Making the tunnel taller is a key element in small sports cars - it's not just to clear the driveshaft. Taller door sills also helps, see my article here: http://victorylibrary.com/mopar/frame.htm
Boffin Emeritus
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Re: Frame connectors
[Re: polyspheric]
#2093889
06/18/16 11:28 AM
06/18/16 11:28 AM
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Joined: Dec 2003
Posts: 22,696
Bitopia
jcc
If you can't dazzle em with diamonds..
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If you can't dazzle em with diamonds..
Joined: Dec 2003
Posts: 22,696
Bitopia
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The greatest load in racking (angular twisting of the chassis by application of power, in which the axle planes are no longer parallel) is bending in the vertical plane. More height increases stiffness, which is why rectangular frame connectors are taller than they are wide. Welding through the floor makes it a structural member, otherwise it's a big tin playing card. Compare the frame rails of 1/2 ton and 1 ton trucks - the height difference is huge. Making the tunnel taller is a key element in small sports cars - it's not just to clear the driveshaft. Taller door sills also helps, see my article here: http://victorylibrary.com/mopar/frame.htm I question the "bending" comment in the first sentence. In maybe a full cage car, I might see the Frame connector seeing bending loads when seeing power induced twisting, besides expected tension/compression, but in our unibody cars, with the stiffest item being the added frame connectors, I'm thinking torsional twist is the bigger stress. Your informative link worth reading, has one IMO extremely important point, often ignored or overlooked and worth repeating, and in design should be followed closely: "every effort should be made to attach the rear of the connector directly to the forward end of the rear spring support structure (spring hangar box, trailing arm pivot, &c.). The forward end of the connector should approach the lower control arm mount as closely as possible." 
Reality check, that half the population is smarter then 50% of the people and it's a constantly contested fact.
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Re: Frame connectors
[Re: Tech Instructor]
#2093952
06/18/16 02:32 PM
06/18/16 02:32 PM
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Joined: Dec 2005
Posts: 11,558
Fulton County, PA
CMcAllister
Mr. Helpful
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Mr. Helpful
Joined: Dec 2005
Posts: 11,558
Fulton County, PA
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How it is installed is much more important than sizes and shapes. Welding a 4' long tube, regardless how stiff it is, to sheet metal at both ends without supporting what is in the middle, will do more flexing of the weld areas at the ends than it will to stiffen the entire unibody structure. Will it help if you decide you don't want to cut the floor? Yes. But it's not as effective.
If the results don't match the theory, change the theory.
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Re: Frame connectors
[Re: Tech Instructor]
#2094974
06/20/16 02:18 PM
06/20/16 02:18 PM
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Joined: Apr 2006
Posts: 4,220
West Plains, MO
DrCharles
master
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master
Joined: Apr 2006
Posts: 4,220
West Plains, MO
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This may be a dumb question, but you're talking about round tube (going all the way through the torsion bar crossmember), right? Could this be done with 2x3 1/8-wall box tubing also? The way I usually see it installed is with a 2x6" piece of 1/8" plate welded to the box tubing and then the plate welded to the rear side of the crossmember...   Sounds like a big hunk to cut out though. 
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Re: Frame connectors
[Re: DrCharles]
#2095020
06/20/16 03:05 PM
06/20/16 03:05 PM
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Joined: Dec 2003
Posts: 22,696
Bitopia
jcc
If you can't dazzle em with diamonds..
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If you can't dazzle em with diamonds..
Joined: Dec 2003
Posts: 22,696
Bitopia
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Not sure what the OP's exact plan was, in my case, when possible, especially when floor pans were removed, I addressed this transfer stress forward issue by adding internal gussets, as needed, inside the TB crossmember where the FC attach. I'd be hesitant to think cutting out big chunks would be best solution, in the big picture. 
Reality check, that half the population is smarter then 50% of the people and it's a constantly contested fact.
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Re: Frame connectors
[Re: DrCharles]
#2095037
06/20/16 03:37 PM
06/20/16 03:37 PM
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Joined: Jan 2004
Posts: 8,257
fredericksburg,va
cudaman1969
master
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master
Joined: Jan 2004
Posts: 8,257
fredericksburg,va
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This may be a dumb question, but you're talking about round tube (going all the way through the torsion bar crossmember), right? Could this be done with 2x3 1/8-wall box tubing also? The way I usually see it installed is with a 2x6" piece of 1/8" plate welded to the box tubing and then the plate welded to the rear side of the crossmember... Sounds like a big hunk to cut out though. Right, just welding to the crossmember is not strong by itself, if tied to the floor pan, much stronger. Have to remember the sills and tunnel are supporting in the same way, just not tied as good. Welding all the seams, instead of spot welds, would help. Enough flexing(after 50 years) they get loose.
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Re: Frame connectors
[Re: Tech Instructor]
#2095050
06/20/16 03:47 PM
06/20/16 03:47 PM
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Joined: Apr 2006
Posts: 4,220
West Plains, MO
DrCharles
master
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master
Joined: Apr 2006
Posts: 4,220
West Plains, MO
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Thanks cudaman. I realize it'd be stronger welded to the floor pan everywhere, but there is considerable disagreement (over on FABO, for example) as to just how much stronger... http://www.forabodiesonly.com/mopar/threads/sub-frame-connectors-please-build-them-correctly.286631/What I really want to know is, could I cut a 2x3" hole in both the front and rear sides of the t-bar crossmember and slide the box tubing all the way through and weld both sides (as Monte recommended with the round tube)? Again, that would definitely be stronger than a plate connection to only the rear face of the crossmember, but will it be enough stronger to complicate the installation that way.
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Re: Frame connectors
[Re: DrCharles]
#2095142
06/20/16 06:21 PM
06/20/16 06:21 PM
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Joined: Jan 2004
Posts: 8,257
fredericksburg,va
cudaman1969
master
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master
Joined: Jan 2004
Posts: 8,257
fredericksburg,va
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Thanks cudaman. I realize it'd be stronger welded to the floor pan everywhere, but there is considerable disagreement (over on FABO, for example) as to just how much stronger... http://www.forabodiesonly.com/mopar/threads/sub-frame-connectors-please-build-them-correctly.286631/What I really want to know is, could I cut a 2x3" hole in both the front and rear sides of the t-bar crossmember and slide the box tubing all the way through and weld both sides (as Monte recommended with the round tube)? Again, that would definitely be stronger than a plate connection to only the rear face of the crossmember, but will it be enough stronger to complicate the installation that way. Are you lining up the tubing with the front frame and rear frame? If so, yes do that. I attach to the frames by going through the crossmember. Just cut out a section of floor over the frame and crossmember then notch and set the tubing down into the frame and x member (back too). More work but you know it's welded strong and will be no flex. Then you have a full frame from front to back, not just a connector. Easier to weld up top too
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