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New to the forum. Didn’t know whether to post this in tech or general. Looking for a yes or no of whether this 6x6 mount is NHRA acceptable before forming and fully welding to body/frame. Doing 8.5 cage for first time. Not new to fab. Just don’t know with the way of the frame and body on the c6 if this will pass or not. Will be running tube through trans tunnel with plates bolted in center to remove to ease future torque tube removal. Any answer/tip is helpful. I understand I can take it somewhere but like most I’m on a budget and can fab myself. Just don’t want to spend all the time to not be passed. Thank you.
Personally I wouldnt bother running that cross bar, your main hoop supports (some people call them D bars or kickers) can go to the trans tunnel on 6x6 plates. Theres a spot towards the rear of the tunnel thats double thick thats a good place to land them. Then you can further brace them across underneath, I used a 1.5” .120 bar forward and back since I also deleted tunnel plate and torque tube.
Ok, the d bars to the tunnel makes sense but maybe I’m going about doing the cage wrong? The cross bar is what I was planning on welding the main hoop too, having another cross bar upfront for the bars running along the pillars and then having rocker bars to connect between the 2 cross bars. Just haven’t seen much and too much misleading info on the proper way of doing the main hoop.
I've seen chassis cars have the main hoop on the crossmember, but rulebook says for frame rail cars to land the main hoop on the frame. Best bet is to consult with the regional guy that will be inspecting the cage for cert as rules are always up for interpretation. Since the frame rail is outside of and lower than the drivers legs technically you don't need the rocker bar but it never hurts.
I've seen a few cars that bend the 6x6 plate 90 degrees, gusset the plate underneath the bend, weld plate to frame, then main hoop to plate. Seen plenty of certified unibody cars that build a box of sorts under the main hoop instead of just a 6x6 plate. Certainly a few options for install.
I did some digging and when a cross bar is welded to the frame its counted as the frame as long as its properly installed. So it should be fine to use as the base of your main hoop assuming its a 2x3 or 2x4 .120 wall similar to building an outrigger on a narrow frame vehicle.
I appreciate you looking more into it. I did get in touch with the regional inspector and he said he hasn’t dealt with any steel frame corvettes, just a handful of the z06 frames. After explaining he said the crossbar way is a safe way in his eyes so there wouldn’t be any issues he could see that it wouldn’t be acceptable. After more thinking and research I think I’m going to go ahead and bite the bullet and just trim the floor as needed to build rocker boxes and just weld the main hoop and front bars to those. I think it will give a stronger platform than just relying on the crossbar welded on each side in the case of rollover. He didn’t say anything about the crossbar needing to be bigger diameter than 1 5/8 for the bars so maybe I’ll ask him about that part the next time I talk to him for future reference if anyone else should want to try the crossbar way and get away with not having to cut the floor to reach the full inside of the frame.
Not sure what you mean by trim/cut the floor to reach the frame. You can put the rocker box or outrigger on the frame where you have your plate now with something like shown below and land the main hoop on it. I got my main hoop very tight to the sides of the car so I welded the bar to the car for a few inches as well, made it very solid even before adding the fore and aft supports.
Yeah with how low my main hoop needs to be to add the rocker bars and keep them below the top of the interior plastic piece on the rocker I can’t get to the bottom of the rocker box to weld it so I need to trim the floor to gain access to weld it. I know with the 8.50 cage I don’t need the rocker bars but I’m still going to add them just for extra safety but don’t want them to high in case of situation I need to get out the car quick.
That is really not the best location. Remove the fuel tanks and go directly to the frame. Verify the tanks clear the main hoop. You will need to remove a piece of the rear bulkhead to access the area to weld the pads to the frame and the main hoop to the pads. Trim the bulkhead panel to clear the main hoop and reweld in place.
Yeah with how low my main hoop needs to be to add the rocker bars and keep them below the top of the interior plastic piece on the rocker I can’t get to the bottom of the rocker box to weld it so I need to trim the floor to gain access to weld it. I know with the 8.50 cage I don’t need the rocker bars but I’m still going to add them just for extra safety but don’t want them to high in case of situation I need to get out the car quick.
Gotcha, I ditched all the plastic stuff in the way.
That is really not the best location. Remove the fuel tanks and go directly to the frame. Verify the tanks clear the main hoop. You will need to remove a piece of the rear bulkhead to access the area to weld the pads to the frame and the main hoop to the pads. Trim the bulkhead panel to clear the main hoop and reweld in place.
I believe the g speed kit uses the location you reference. But its the same frame that runs under the door, the b pillar then bends upwards to the location you suggested. Just more cutting to get to that spot, but that would work fine as well. Keeping in mind the rule of the main hoop being within 6” of drivers head, that might be too far back for some drivers. Technically I don't believe the corvette counts as a “frame” because its not at least 1/8 thick so you still have to run spreader plates. I bent the 6x6 plates and used them to saddle the “frame” to support the bars.
Either way all these solutions are more secure than the bolt in bars that drill through the floor and saddle the flimsy sheet metal as a support.
C6 roll cage help.
