How much cage do I really need?

[astroracer]

I am in the design stage for the roll cage for Bad Ast. I am having a hard time finding any data that tells me exactly how much cage I need to be drag strip or road course legal (if there is such a thing for an astro van...)
It will carry three passengers easily but, if I do race the van, there will only be one (or two) bodies inside. Do I really need to cage the full interior? Would a mini-cage (read that F-body size) suffice if it was built to NHRA rules?
Any help or thoughts would be very much appreciated.
Mark
Here are a couple of current pics to help the process.

[John Wright]

Build a cage around the occupants and not worry about the rest? I figure the idea is to keep the sheetmetal from collapsing in on you if the thing gets upside down, provide positive attachment points for harnesses and to add some structural rigidity for the chassis as a bonus. Seems there where cages posted on here in a Nomad, and/or other station wagons that might help give you some guidance. As for the legal stuff, I suppose the event specific rule book(s) would be the best guide depending on what events you propose to run in.

[Bryce]

Get the rules for each class you want to race and build to the most stringent.

You need to be concern with bend radii, the amount of bends, weight of the car and how it impacts tube size and material choice, intersection points, cleaerance for street driving, how you will tie into the chassis. With a full frame I think it needs to tie into the frame.

[67zo6Camaro]

Just as Bryce said.... but as a quick rule of thumb for a 3,500 lbs car/van; you will need a 2" main hoop with .120 wall DOM or chromoly. Supporting halo and main down bars need to be the same with gusseting bars allowed at next size down. There are some bend and cut restrictions on the main supports and down bars. Attachment should be to frame, but it is allowed to get close if you use a 6" x 6" .120 plate at floor. Typically the rule books will have some sample drawings to help you design the cage.

[MonzaRacer]

Actually from looks of it ther shouldnt be much issue with a cage. For that unit the typical halo bar tucked well up next to roof, down tubes right next to a pillars and all. Unless it gonna be some super high power rig my bet is the rear bars could go back above the door, then drop down to tie into rear rails, jsut keep everything good and tight to the body. I helped a guy put a 454 in an old Astro and we kept the the bars away from people. He had all but a few spots where everything fit under plastic panels and he installed 5 extra seats plus driver/passenger seats and no one came any where near the bars and all wore either adapted 3 way stock of 4/5 way harness. Kind of weird seeing his van with him, wife, 4 regular kids and one baby seat that could be in back or right behind driver/passenger seats.
We tied his stock sub into connectors and remade rear spring mounts in front. The van sat great after we settled the sub frame, and worked with Detroit/Eaton on multi leafs to replace the fiberglass mono leafs.
I try to dig up drawings of the cage and pics but thats almost 20 yrs ago,, not sure exactly where they are if I have them still.
Oh and his door bars we made with a spring loaded setup that has a sleeve that slides over the toothed catches made from solid steel an welded in, we also made the door bars a y in front that went back to the rear hoop and they could be removed for daily driving. NHRA tech crews passed him with nary a whimper but I think hes only good to about 9.5 or 10 sec in 1/4.
Van engine got rebuilt as a 427 recently with newer MS3 EFI and rebuilt the 4L80E and used the MS GPIO to control it as his old school bus computer was pain to reprogram,,,and it gave him ability to add in paddle shifter.
I built a lever to latch the door lock sleeves , kind of like a door handle pull back slide sleeve down to release and open door. had a small collar teflon lined so door bars would move with door as it opened. the lever was clearances toward the door panel, so you couldnt catch it while driving.

[astroracer]

Thanks guys, thanks Lee,
I am going with NHRA rules for the most part. 1 5/8 x .188 mild steel is what they call for. Should be good enough for some bracket racing which is all I plan on. I have held off on any cage work until we get the tin work wrapped up. I really need to get final front seat positions and heights which will drive the main hoop placement.
If you are following my build thread you know the doghouse flange area is 99% complete and we have started on the rear wheel well rebuild so it's getting there.
I am planning to have the cage welded to the body with the requisite 6" x 6" plates. Inboard angled bars will pick up points located directly over the body mount areas so the cage should be plenty strong. I plan on building two hoops. The main hoop behind the driver/passenger and an additional hoop behind the "back seat" passengers to carry the down bars from the main hoop down to the rails in back. I am working on the cage designs in UG so I should have some drawings by the end of the week.
Thanks for the input, I appreciate it. Any other concerns or comments are welcome.
Mark

[djorgensen3]

You meant 1 5/8" x .118 DOM mild steel right?

[astroracer]

You meant 1 5/8" x .118 DOM mild steel right?

Yes Sir.