frame stiffening / subframe connectors

[sigmfsk]

This is a collection of subframe connector links and info from
www.bluesbrotherscentral.com/forum/topic/6578-make-your-bluesmobile-handle/page__hl__+make%20+handle__st__20
and my BBC Marin County page.

----------------

I'm looking for frame/body stiffness. This page talks how one can ripple the quarter panels with even a mild engine:
> - Frame Connectors:
> You will have to fab these, but pretty simple. This big uni-bodies are surprisingly
> stout, but there is flex. My Fury had rippled quarters with just a 318 to prove it!
www.cbodydrydock.com/forum_viewtopic.php?6.74655.10

so subframe connectors are a must, and maybe even more bracing. I figure whatever I can weld in underneath is good, as I won't be installing a roll-cage. Here are some interesting links:

beautiful pic of torque boxes:



from
www.cbodydrydock.com/forum_viewtopic.php?5.39078.20

other info and pics:
www.cbodydrydock.com/forum_viewtopic.php?6.31020
www.cbodydrydock.com/forum_viewtopic.php?5.36682.0
www.cbodydrydock.com/forum_viewtopic.php?5.49071
www.cbodydrydock.com/forum_viewtopic.php?5.51735

take a look at the sets of pics for August 2007
satellite.uruuk.com/timeline_p3.php

Auto Rust Technicians previously offered subframe connectors for c-bodies, but no longer. This web-page
www.autorust.com/sitemap.html
still shows the link for "68-74 C-Body". I called them, and they agreed that it should have said "-73 C-Body", but it doesn't really matter because they don't offer them any more.

Their web-site has several good articles about frame stiffening via subframe connectors and torque boxes:
www.autorust.com/articles.html

Here's another subframe connector/torque box article:
www.moparmusclemagazine.com/projectbuild/mopp_0612_classic_barracuda/index.html

I took a look underneath the car, and it may end up that the strongest subframe connectors would intrude up an inch into the rear floor pan areas. If that ends up being the case, I could probably live with that.

---------

ghostbluesman wrote:
> I used mild-steel U-channel on my '68 Dart when I dropped the
> 440 into her; you could feel a definite "stiffening" of the frame
> when you lit 'em up on the tarmac and put the torque to her...the
> SFC's are really a good addition; as a matter of fact, I'm thinking
> about adding them to my Falcon wagon. :wink:

---------

Here's a thread discussing these frames and other stiffness possibilities:
www.montecarloss.com/community/ubbthreads.php?ubb=showflat&Number=796325&gonew=1

This post:
www.montecarloss.com/community/ubbthreads.php?ubb=showflat&Number=812788#Post812788
has this pic:



that outlines a poster's earlier comment:
> For the stock frame, I easily agree that those C-channel mid sections are a key source
> of torsional compliance. When I stiffened them by adding a 1/8"-wall steel box tube of
> 1" x 3" cross-sectional dimensions, running from the front wheels to the back wheels
> and connected with those central frame rails, the improvement in rigidity was significant
> and immediately apparent.

-----------

I found this thread:
board.moparts.org/ubbthreads/showflat.php?Cat=0&Number=5697053&Main=5693878
with this post
> I have installed frame connectors and torque boxes...
with a link to this album:
s11.photobucket.com/albums/a199/2445Cline/GTX/
with these underbody pics. Looks nice.



------------

One of the links that I posted earlier
www.cbodydrydock.com/forum_viewtopic.php?5.51735
shows the subframe connector in this pic:



that overlaps the rear crossmember and welds to it.

That same thread has these pics:



of a different car showing how this method resulted in the rear floor pan being cut into.

This thread:
forums.vintage-mustang.com/track/543451-underriders-caltracs-slide-links-etc.html
shows subframe connectors in this pic:



that go completely under the rear crossmember and weld to it.

The method shown in that last pic might allow the rear floor pans to not need to be cut into.

-----------------------

Here's a pic of challenger subframe connectors (showing how they raise into the rear passenger floodboard area)



from this fascinating thread:
www.horsepowerjunkies.com/forums/showthread.php?t=36751&page=19

and some other pics from that thread:





----------------------

Here's a page on a buildup of a 1970 dart swinger
www.schwartzperformance.com/projects.aspx?projectid=21
that has some nice pics of underside frame upgrades:



----------------

Here's a guy that's turning a 76 Gran Fury Brougham 4-door sedan into a police-clone,
> street-strip-show car with 500 cubic inch powerplant and 3.90 rear axle ratio.
www.cbodydrydock.com/forum_viewtopic.php?5.86767.0

Looks like it's going to be an impressive build.

pic showing the extra longitudinal welds along the front subframe:



He's planning on subframe connectors and such; there's a great opportunity to share info between the boards. More pics on the thread referenced. Now that I think of it, I should post this thread over there as he'll probably be interested in this "handling" info.

[note, that was before BBC went offline. I suppose I should update him with this new thread]

[sigmfsk]

On BBC, I wrote:

take a look at the sets of pics for August 2007
satellite.uruuk.com/timeline_p3.php

and then copied that to the post above. The link is dead - the entire uruuk.com is dead. When I copied the link from BBC yesterday, I attempted to check the internet wayback machine, but it was not working at the time. I checked now and all I can find is:

web.archive.org/web/20090627070856/http://satellite.uruuk.com/

Google searching for
1970 plymouth satellite "project black car"
yields only the dead-link, and the BBC page where I reference the link.

That satellite thread was a cool writeup. If you think of a way that I could contact the owner, please let me know. I'd love to catch up with him and see what happened to his project.

thanks,
arthur

[sigmfsk]

Dec 2011 "Mopar Action" has this pic of a 70 Charger roadster:



The article says:
> Patrick came up with 2x2" square subframe connectors and a round
> tube subframe cradle with a large X-brace...The beefed chassis is
> very stiff. You can jack up the car from any corner and still open
> and close the doors. There's no flex at all.

Interesting.

[sigmfsk]

That x-brace on the Charger fascinates me.

I just can't imagine why he didn't use an X. Like this 1990 Corvette convertible:



from
forums.corvetteforum.com/c4-tech-performance/1500152-downside-of-removing-convertible-cross-brace.html

Herb Adam's "Chassis Engineering" book has a nifty section on testing out ideas of torsional stiffness by using balsa wood models.

Some of that info can be seen here:
www.cobrakit.com/Chassis/ChassisBasics.htm

> When a crossmember is added, there's approximately a 50
> percent improvement in the models torsional stiffness

I think I understand the utility of an x-brace. I don't know why one would want to change from that to the design shown on the charger.

I found that the place that did this 70 Charger is the same outfit that did the 69 Charger that I use for reference pics for the March pulley set I plan on using my on my 440.

His page here:
www.scotlea.com/ChargerRoadster.html
has these pics and many more of the 70 charger.



And this page
www.scotlea.com/scotlea_frameset.htm
has tons of pics of the 69 charger

[sigmfsk]

Talking about those corvette convertible braces, here's where a guy boxed in his brace:

from
forums.corvetteforum.com/c4-general-discussion/2875676-installing-a-convertible-x-brace-on-a-96-coupe.html

Here's an aftermarket replacement:



Interesting crossover.

Surely the round tubing the charger used would be stiffer than this, welded all the way throughout. But why not just make an X, and why not have the ends of the X go to the ends of the car?


Here's a BMW E36 M3 cross brace:

from
www.teamspeed.com/forums/m/35345-story-my-e36-m3.html

[
edit: found info on it here:
www.bimmerhaus.com/raceprep/M3facts.html
> Chassis X-Brace
> I use the BMW factory chassis "x-brace" which triangulates both
> sides of the lower portion of the transmission tunnel for added
> stiffness. This brace comes standard on all M3 convertibles, the
> M3 LTW, and all Z3's.
]

A 67 Camaro convertible had this crossbrace:

from
www.67yenko.com/images/general/pages/583473-700-0_jpg.htm


Here's an interesting article.
kit-car.org/Files/Chassis/kitcaranalysis_V2.doc

which has this portion on an x-brace:

> the X braced frame is stronger, lighter and simpler.
I hear you, brother!

It also has some good links. This one:
www.ultimav12.ca/
has detailed information on the chassis stiffness improvements (if any) that resulted from each change they made to the car.


> Roof sheet metal brought stiffness from 8800 ft/lbs/deg. to 9500 ft/lbs/deg.
That surprised me. The interior of the bluesmobile can't look different than stock, but I could stiffen up things behind the panels and under the fabric headliner monstrosity.

I'm thinking that's not worth the trouble though. Just put in subframe connectors, torque boxes, and a giant X brace underneath and be happy with it.

[sigmfsk]

Here:
www.rs25.com/forums/f9/88813-homebrew-x-brace-gc-chassis-11.html#post1746934
the writer refers to this:

as a "double-K". He has strong opinions on it:

> gusseting an X member may be needed, but could be minimalized
> if not avoided alltogether with a redesign... when tying together
> the rails of a hot rod, you wouldn't use an X, you'd use a K... a
> stout K member is stronger than a X member..... it still uses
> triangles for strength, but less intersections makes it stronger..
> the X doesn't mind twisting in the middle, especially after some
> welding has slightly weakened the steel at the intersection
> point... but a K member uses a thicker cross beam, then smaller
> legs from it to gusset itself, making a very strong crossmember,
> and the industry standard, prolly since before I was born..

It seems that a K is better than an X because there are less intersections at a single point, which makes it more resistant to fatigue.

> From a structural engineering standpoint, "K" braces (we call
> them chevron or v-bracing) does have merit, especially when it it
> comes to seismic detailing, which actually shares a lot of
> similarities with car brace design. As with vehicles, buildings and
> bridges are most susceptible to failure at points where many
> connections intersect. All other things being equal, if you can
> minimize the number of connections at a single point, the
> structure will be much more resistant to fatigue related failure.
www.rs25.com/forums/f9/88813-homebrew-x-brace-gc-chassis-12.html#post1746994


> I'm still sure a fat K member will outperform the X member. I'm a
> platinum certified I-CAR tech, in unibody frame repair, and regular
> chassis frame repair, amongst other things... so I'm not just
> pulling this out of my ass, here...I've been trained to understand
> the way inertia and torsion effects the skeletons of modern cars.
> You just don't see X braces used anymore... everything should be
> triangulated, and a K is two triangles(three really).. an x member
> creates a weak point, the K cuts this weakness down
> considerably.
www.rs25.com/forums/f9/88813-homebrew-x-brace-gc-chassis-16.html#post1749238


Well, I guess that makes sense. A K might not be stronger than an X when it was first made, but it might be a lot stronger after the X fatigues and the K remains strong.

Of course, now that I read that, and see the pic above, I see it really has minimized the intersections at a single point. Even the legs of each K don't intersect.

That frame pictured above looks pretty stout. Now this:


from
www.gmhightechperformance.com/tech/0802gm_2002_chevy_camaro_ss/photo_06.html

looks flimsy city. Of course, looks can be deceiving, and it actually may add a lot of torsional stiffness, but I'd expect that charger to beat this thing 6 ways to Sunday. The article calls it an X, but it looks like "double-K" may be a better term.

Now this seems like a good use of a double-k: if you want the driveshaft to go through the center:

from
www.hotrodscustomstuff.com/OLD_SITE/DS-frame.html

and these two


from
www.customclassictrucks.com/techarticles/0509cct_1940_ford_chassis/photo_42.html

This isn't a "double-K", but it has two K members:

from
www.hotrodders.com/forum/do-i-need-x-brace-my-chassis-113053.html?s=c85969a5e17daa5f779ddc9e3d1d59af

and if a double-K is good, how about a double-X ?

from
www.k-series.com/showthread.php?10997-D3-double-x-brace&p=55853&viewfull=1#post55853

This pic:

from
50mustangsuperfords.automotive.com/42517/15518-maximum-motorsports-suspension-kit/photos2-0.html
reminded me to not forget about stiffening up the front subframe.

Here:
www.forabodiesonly.com/mopar/showthread.php?t=146986
I learned:
> Call the guys at Firm Feel. They have a kit of gussets that are
> designed to be welded into the K frame to make it stiffer. They
> have pictures of modified K-frames on their website.

I see info on firm-feels website:

> The factory welds are rewelded and we weld the seam all
> around. The steering box mount is boxed, gusseted. L.C.A. pin
> reinforcement plates are welded in. Reinforcement plates are
> added to the strut mounts.
www.firmfeel.com/reinfkfram_b.htm

Nothing for a c-body, but I didn't expect that, I'm just interested in the concepts.

[sigmfsk]

So we have this guy with the exhaust under the bracing:



and this guy with exhaust over the bracing:


And here's a guy with both:

from
www.fastlanerodshop.com/5window/exhaust.htm

It seems that having the bracing up against the floor (and welding the floor to it) would provide the best rigidity. And having the bracing down as the lowest point would be best for protecting the trans pan and flexplate. Why not choose both? Not something like the above, but something that runs the exhaust through the frame, like these:


from
Art Morrison
speedhunters.com/archive/2010/06/24/car-builder-gt-gt-a-visit-to-art-morrison.aspx

or this Corvette:

from
forums.corvetteforum.com/c1-and-c2-corvettes/1962512-exhaust-through-hole-clearance.html

Here are some that I thought interesting, but really too dainty for my setup:

from
www.britishv8.org/Articles/TR3-Plus-4-part2.htm



from
www.britishv8.org/Triumph/KenHiebert.htm

I've pretty much settled on a solid motor/transmission mounting. Why not the exhaust? Make it a solid part of the car?

This guy solidly mounted his muffler to the frame:

from
forum.ih8mud.com/fj55-iron-pig-preservation-society/518103-exhaust-out-front-rear-tire-bad-idea.html

I'm thinking that it would be fine to have the exhaust not solidly mounted to frame / floor pans, and just have it going through the frame as in that Art Morrison setup. Attaching rugged exhaust tubing solidly may make it strong, but may also increase interior noise. And certainly would increase heat transfer to the interior.

> My car has solid engine and exhaust, never broken anything. I would
> consider some flexible mouting in the interest of sound, but mounting it
> solidly allows you to gain the maximum clearance.
www.bmw2002faq.com/component/option,com_forum/Itemid,0/page,viewtopic/p,922793/highlight,/sid,7bc0520bd11e1b362ea8ebcb4656042b/


This guy use oval tubing for more ground clearance (on his 180 degree header system):

from
www.jalopyjournal.com/forum/showpost.php?p=5353172&postcount=1