Roll bar question

[AlanCasida]

Over the weekend I looked closer at putting a roll bar in my 66 Galaxie. With the perimeter frame and the sunken floor board(it’s not flat) it will take a lot of cutting to get it mounted to the frame. The frame basically fits up in a channel in the lower body. That got me wondering why it has to be attached to the frame other than the NHRA requires it. At first I thought it might be because the floors are thinner in full-frame cars compared to unibody cars but now I don’t think that’s the case. I have a few other theories too. What do you guys think?     

[machoneman]

It's one of those rules IMO that makes sense: make the roll cage as strong as possible by integrating it into a frame, where present. Now, if your not going NHRA racing (nor other racing venues that require frame mounting) then you can skip it and act like it's a unibody car and weld it to floor plates. JMO!   

[MRadke]

I think that if you stiffen the body with the roll bar without attaching to the frame, you will rip the body off of the frame, with any kind of horsepower.

[jayb]

NHRA rules specify that for a full frame car, the roll bar has to be attached to the frame.  The 1/8" plate approach is only acceptable for a unibody car.  When I did the cage in my '64 Galaxie, I cut a hole through the floor and ran the roll cage tube down beside the frame, then used gussets to attach it to the frame.  But when the NHRA tech inspector came over, he told me that was not acceptable, and that I had to have the bar welded on top of the frame.  He let me put bars from the main hoop at an angle down and attach them to the top of the frame, and then gave me the chassis cert.

As far as I know the best way to put a roll cage in a full frame car is to cut a hole in the floor that is big enough so that you can weld around the tube that goes down through the hole to the frame, then make a patch panel to cover that hole after the bar is welded in position.  Also, make the hole large enough so that the hoop and back bars can be slid over and dropped down beside the frame.  That way you can bend up the bar and get it tacked in place up at the top, then slide the whole thing over so that the whole cage drops down through the floor a few inches.  That will give you clearance to weld up the front and rear bars over the top of the main hoop.  Then, just put it back in place before you weld the main hoop and rear bars to the frame of the car.

Good luck Alan!

[57 lima bean]

http://www.nhra.com/UserFiles/file/General_Regulations.pdf       4-10

[cjshaker]

Even on unibody cars, the roll bar is typically welded to the top of where the frame or front/rear torque box is. It's just reinforced with plates so that it's not solely relying on the thinner sheet metal that covers the top of the frame. Even rear bars are welded to frame crossmembers if not the outer rail itself. If you only weld to flat sheet metal, such as an open floor pan, then you've only created an area for the bar to punch through in the event of a rollover.

[turbohunter]

"installation of frame connectors on unibody cars does not constitute a frame; therefore it is not necessary to have the roll bar attached to the frame."

This is the most interesting passage to me.

[machoneman]

Yeah, they left out the very last word: "connector"

[fairlanegt427]

I put the angle kickers ill call them from the main hoop to the to of the sub frame on my 65 comet.   I hated to cut those holes in it to fully weld those 2 tubes but wow did it stiffin up the whole cage/car.  imo

[jayb]

NHRA calls them the "D" bars, referring to the drawing in the NHRA rulebook.  I did the same thing with my Mach 1, and I agree that this did stiffen up the car.