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Discussion Starter #1
So obviously you can’t get a torch on the top of a roll cage because of the roof. This video says you can either build rocker boxes or the other alternative is drilling holes in the floor to drop the cage down, weld it, and then put it back up.
Well, NHRA guidelines don’t allow for rocker boxes (he was building a road racer) which leaves only drilling holes in the floor which seems like a piss poor way of going about it. Cutting holes in a perfectly good floor seems nuts to me. Is this really the only way to do it or is there more than just what this guy knows?
 

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Drop it through the floor, weld, then raise, or use gussets
 

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The round holes drilled in the floor which are slightly larger than the roll bar o.d. will be welded back in, and your 6" square reinforcement plate will be welded over the holes. Non issue.

If your cage is not too tight against the roof, a small tig torch can sometimes make a full weld.
 

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NHRA allows a specified size gusset if you can't weld all the way around.

I was fortunate and just cut the roof....Also allowed me to get the bars pretty tight...


For cars being built to the Rulebook Spec (i.e., 8.50 seconds e.t. and slower), there are times when it is not practical to fully weld the windshield bar and/or the main hoop to its adjacent structure. In this case, the use of two (i.e., two per affected joint) 1 3/4-inch x 1 3/4-inch x .110-inch 4130 chromoly or mild steel plate gussets, fully welded on one side, may be used to replace up to 25 percent of the weld. These plate gussets may have a maximum of one 1/2-inch-diameter and two 5/16-inch-diameter holes. Another option to correct these incomplete welds is to use two, fully welded, tube gussets per affected joint. These tube gussets must be a minimum of 3/4-inch x .049 4130 chromoly or 3/4-inch x .118-inch mild steel and at least 4 inches in length. These gussets are an acceptable correction to incomplete welds only in the OEM roof area.
 

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I drilled 2ea 3" diameter holes through my newly installed floor behind my rear torque boxes to drop the main hoop down to access the top of the front down bars. (SCCA spec)

IMG_20140411_175332.jpeg


I also constructed the halo bar to the main hoop, temporarily supported by the forward down bars, welded what I could and removed it from the car for final welding and paint prep.

IMG_20140408_193432.jpeg


The holes in the rear of the car were to attach the forward down bars to the halo.

IMG_20140411_174835_zpsuqs0mhec.jpeg


While it is slid back, if it is a multi point cage, install your door bars so you can access the tubes for 100% welds without drilling holes in your body. I prefer to remove the roof skin to install cages, especially when the cage it really tight to the body of the car. The halo bar in this cage is barely visible from outside of the car. It gives maximum head room and lots of room to get in and out of the vehicle.
 

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Discussion Starter #7
Looks like holes in the floor it is. Thanks guys. Do I have to weld the sheet metal back in place or will the 6x6 floor plate be good enough to pass inspection (specifically NHRA)?
 

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If you place your holes behind the rear torque box through the single floor thickness I would definitely weld them shut. I would also recommend installing your main hoop on top of the rear torque box lids. I prefer not to weld plates to the thin floor pan, even with the recommended plates, unless there is no other placement available. I would want the bar / cage to be extremely functional IF it ever has to be used. Do not skimp on any attachment points or construction methods.

738268
 
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