Hi Everyone,

I am in process of installing an 8-point roll bar in the Duster and have been considering installing a set of subframe connectors. Is this necessary with the roll bar? Any suggestions on brand versus making them out of 2x2? Any help would be greatly appreciated.

Thanks,

Jon

My opinion is that if you are installing a roll bar - then subframe connectors would be an obvious upgrade. You may even be able to tie the cage to the connectors with the main hoop - or the bars coming off of the hoop.

I have 2x3 or 2x4 box tube subframe connectors in my demon with an 8 pt cage all tied together.

Yes.. put the connectors in.. drop the angled
bars of the main hoop onto the connectors for
added strength.. I build them for customers
out of 2X3 tubing

Always

I use 2x3 .083 and section it up into the floor. The rear half of the connector will slide into the front of the rear frame rail (on a stock rear frame car), be sectioned up into the floor in the passenger foot area, go back under the floor 100% under the front seats and butt against the rear of the torsion bar x member just outside the torsion bar sockets. This makes maximum use of the frame tie to stiffen and tie the car together. The main hoop diagonal can be attached right to the top of the connector. This diagonal is required on a full cage anyway and a good idea on even a simple bar.

I know everyone suggests 2x3 connectors and sticking it up in the floor, welding solid, etc, etc. While that in no way hurts anything, I feel it is far from required. 2x2 will be plenty

I put the 8 point cage in my late B a few years back. This is a big unibody car that they don't make anything off the shelf for ( cage / subframe connectors). Before the cage install, I was running mid 11's and starting to wrinkle the rear fenders by the B pillar posts. I installed a highly modified E body 8 point cage. What I did to stiffen the middle of the car was to add a bar near and parallel the floor between the main hoop and front down bars ( pic). Since my main hoop sat over the front part of the rear frame sections and the front down legs sat over the rear parts of the front frame sections, I essentially made a box over the area where there was no frame. I was going to fab up some sub frame connectors, but decided to try it without them. I still might in the future, but the car now runs mid 10's with no body flexing that I can visually see.

I really like the way dvw ties the subframe connectors to the rocker, then attached the cage to that member.

https://board.moparts.org/ubbthreads/ubbt...age.html#UNREAD

That's the way it should always be done. Tubing landing on the 6x6 plate welded to the floor pan doesn't tie cage into chassis very well

Those longitudinal bars function as subframe connectors, as long as the hoops are secured to the chassis.

Whatever you decide on, don't go crazy on wall thickness. Even if you do 2x2, 0.125 wall is as big as I'd go.

One other thing, all steel has the same spring constant, so even the lowliest piece of 1019 hot rolled will have the same stiffness as a piece of 4340. The low carbon steel will be much easier to weld, so don't get fancy.

R.

IMHO the optimum height of the connector is a function of how much power, how much traction, and the wheelbase (longer = more flex).
On paper, 2" wide X 3" tall is much more rigid than 2 X 2 (over 2-1/2 times), the question is "how much is enough"?
I wonder if anyone has done a specific size install (2 X 3 etc.) and tried to jack up the left front, and measured how far off the ground the right front went up vs. another size?
Obviously, at some point the connector's stiffness exceeds that of the remainder of the chassis, and the right front will come up simultaneously.

Actually, The floor on most unibody cars makes up the top half ( welded to ) the front and rear frame sections on a unibody car, which makes the frame a square tubing as it attaches to the unibody. It is just as strong as any full frame car in those areas. As long as your 6X6 plate is welded to the floor above the square tubing frame area under the unibody, you are essentially welding your plate to the frame sections, or top half of the square tubing. Adding subframe connectors, will help stiffen a unibody car, but does not qualify ( NHRA rule book wording ) a unibody car as a full frame car. Attached pics is 6X6 plates welded directly over the rear frame section ( square tubing ) for the hoop and rear down bars.

There is strength in the stamped sheet metal parts that form the body. Just like a simple bead in a piece of aluminum makes it stiffer, the piece of sheet metal that is stamped to form the floor becomes much stiffer. By attaching and/or tying the cage and frame ties into the body structure as much as possible, and in as many areas as possible, you are creating a much stiffer assembly. A frame tie attached only in the small areas at the front and rear ends of the tube will still flex the sheet metal in the area where it's welded. Attach it to a substantial part of the floor in the center of the tubing, and you increase the rigidity of both. One can't move without the other moving also.

2 things. The top part of that rail (the floor) is only spot welded to the top flange of the rail, and both are formed from much thinner material than floor plates or even .083 box tubing. So now you have piece of .032 sheetmetal with 6, 8 maybe 10 1/4" spotwelds attaching that floor plate to that frame rail. Now there are some builders who will go through a unibody car and stitch weld all those spot welded joints to stiffen the body structure before even starting on the chassis, but usually only on higher end Super Stock, Comp cars, etc. Also, by using connectors or "outriggers" between the framerail and the rocker, which is also a substantial part of the strength of a unibody, and even welding that connector to the floor pan between the framerail and rocker, the body and the cage both benefit from the additional support.

Most don't put their hoops on the raised crossmember that you did. Most weld a 6x6 plate on the floor pan in front of that in the rear footwell. Welding in an outrigger is much better in either case

What I do on stock type cars when putting in
a roll bar is to keep the main hoop out as far
as possible.. this will land on the rocker/sill
plate area.. you still have to put in the 6x6
plates.. I bend that plate to fit the sill.. part
of the hoop will land on top but part will be on
the downward angle.. I cut the hoop to fit that
angle.. then I fit the angled down leg to land on
the frame connector... doing it this way keeps the
main hoop out close to the side of the car to maximize
the interior space and IF you wanted to add more strength
you can add(if needed) short brackets to the B pillar if
it lines up with it... most guys wont do this if its a
street car but if its a race only they gain some strength
doing it.. on a full tube chassis I dont bother being that
the chassis has the strength and the body is just along
for the ride
EDIT
if you put that 6x6 plate on the bottom of the
foot well area.. or anyplace like it.. its just
there t increase the surface area with the 1/8"
material.. its a much greater area to tear out
in a crash/roll over

And that last part you posted is exactly what most guys do. And then when you look underneath, not only is the plate just on the sheetmetal, they also blew the sheetmetal full of holes attempting to weld the plate to it

On my car, I believe the area you are referring to is just in front of the front of the rear spring hanger mount. I did weld (from the under side ) in between the factory stitch welds in this area ( where the 6X6 plate sits ). The plate does not sit directly over the frame though, which I believe Monte was referring to. About 1/2 the 6X6 plate (inner portion) sits over the frame. Not ideal, but - - - . The rear down bar 6X6 plates do sit directly over the frame. My floor pan was also in 2 sections ( just in front of the Hoop mounts ) and stitch welded as you said. I welded that up also. Probably helped stiffen the middle of the car also.

The rear half of mine. I found 2x3 sub frame connectors (though over kill in size) to be a good fit and able to attach to the entire floor pan. There are plates welded to the inner rocker to spread the load as well. Easier to take the floor piece out and reinstall when finished.
Doug