I currently have a MS cage in my Demon and am wanting to switch to a CM for smaller diameter bars. I have seen pics of cars with CM cages tied into the stock chassis and I am wondering how one does that. I can only presume the chassis is MS and that the CM cage is welded to it directly.

Look at my "Coming To A Strip Near You 25.5 Challenger post. Obviously,mine is an E Body but same principle for your car. My chassis and full cage is all c.m. and is ran through all the stock floors and firewall.

Thanks I’ll check it out

No one reads anything but their own post.

You may have MS frame ties or you may be looking at getting it welded to stock floors or frame rails. That is acceptable, the rule says any weld that affects CM needs to be TIG. MS to CM, CM to MS and CM to CM are all TIGed. Beyond that, rules for construction are pretty much the same until you get to an SFI certified situation. The rule book is pretty detailed in it's requirements.

Also, using ChromeMoly instead of Mild Steel doesn't allow you to use smaller diameter bars. Just reduced wall thickness. Doing a cage instead of a bar allows you to use 1.625 instead of 1.750 diameter.

Another thing is resale. A moly car will always be able to bring more $$$ over a M.S. car due it being able to cert or re-cert & usually less weight when compared to the amount of bars each car would have.

Cage specs from SFI/NHRA usually do not effect tubing diameter, but wall thickness. Before you decide to change out, make sure that if will work with what you have in mind.

Actually I did read your post, and regarding your statement about roll bar vs cage being the determining factor in bar size. I appreciate the correction. I however currently have a cage so in this instance it does allow for me to go to a smaller diameter bar.

Thanks for your original input

6PKRTSE, I have owned the car since 94, she ain’t going anywhere. Even if it only stays a street car. A lot of great people have helped me since I was a dumb 19 year old kid on this car and no less than two of them are no longer here.i have the trunk flooring and the windshield bars I want to change so now seems like the best time to change it all.

You know what you want. That's what matters. I agree with your plan.

A 6x6 plate is welded to the floor pan. If the plate is moly it's TIG welded. But most use MS and tig a moly pipe to that plate.

I would try and get a copy of the current SFI specs on a NHRA legal cage, it will have the correct minimum tube diameters and wall thickness for both C.M and M.S.
The main hoop bar on a roll bar is 1 3/4, on a cage it is 1 5/8 is what I remember now
If your thinking of having it certified later to faster than 7.50 ET in the 1/4 it has to have a all C.M. cage, not mild steel is what I remember a friend finding out the hard way later after having his new race car built with some M.S. bars in it

I personally don't like installing a bar or cage on a 50 year old floor pan. Outriggers to a plated rocker make way more sense to me.
Doug

I also copied Doug's car and used 2x3 between the frame connectors (welded through floor) and rocker box. I had a really hard time welding to the rocker box due to contamination in the box itself. Not sure how to get in there and clean the backside of the box where the 2x3 is welded.

After I hole sawed through the top of the outrigger to locate the main hoop. This allowed me a solid fore-aft measurement for the roof halo, which works good in a 66-67 b body IMO. Once you have the roof halo leveled and tacked in you can raise the halo/main hoop up and slide a place under it to get the a-pillar bar measurements. I am 50/50 at this point between plates and outriggers on to land the forward bars after all of the trouble I had welding to the rocker box. At lease I can clean both sides of the floor pan for the plate.

That said if I was starting from scratch and not as a broke 19yo I'd have the car blasted before doing anything. The latest rendition of my red Charger has been the slowest going because the car is painted. If you google the NHRA rulebook 2017 is puplished and for what you are looking at it's the same as my 2018 book.

hth

Not always, especially when you have yourself on "ignore".

As pointed out the only thing to consider is where welding of moly is concerned is the moly tube HAS to be tig welded in place. You will see a minor weight savings from MS to Moly n a simple cage. It wont be a ton of weight to be sure but some. I also prefer outriggers over plates on the floor

I've always preferred to do it this way. I like to use 2x3 and section it up into the floor, sit the bars onto - or into - it above the floor, tying the chassis, cage and floorpan all together. This as opposed to the outrigger being under the floor with the floor trimmed around the bars. The 2x3 can be mitered and made to fit nice and clean. Most people think this is too much work, but it makes the car safer and stiffer.

My point was that when people who weren't interested enough to post correct information assume that no one else has, they're just wasting my time.

My new rule: assume everyone already knows everything, and never makes mistakes.
Yup, that'll work.

And a note on Mild Steel, it's not all the same. ERW is a welded seam tube, typically made from 1010 steel. It's cheap and the wall thickness is hit or miss, which is why people have to use heavy .134 wall stuff to make sure it passes tech.

DOM is much more accurate and typically made with 1020. Usually you can use .120 wall with a .118 minimum spec safely.

ERW is really crap. Running a drill bit through both materials really shows the difference in them. Both are considered mild steel, costs are different.

I would go only one way if starting over. Build your cage, then attach your car to it. Front and rear frame rails attached with subframe connectors are your starting platform, build up from there. Sheet metal is just hanging there, but like my inspector said, you have two cages, body and roll cage.

Exactly. The formed sheet metal body is also a stiff and substantial structure. Use it. With some planning, the body and the new chassis/cage can be made to support and reinforce each other, making the assembly stronger than if the body was just along for the ride. Tie them together, beyond the mounting points called for to get the cage in the car, to create one assembly

You said it better than me, thanks

Much easier to remove a section of the floor. Weld in the cage and outriggers. Then trim and weld the floor cutouts back in.
Doug

I’m not sure who you are referring to, however I have noted on numerous occasions rather than interject positive helpful replies you post your feelings and then get butt hurt when not everyone agrees with you. My statement is correct, going to a CM cage allows me to use smaller bars, why because I have a MS 10pt cage already. So you assuming you know everything about my car gets old. So please do us all a favor and either start posting useful info or just don’t post. I don’t have time for you getting all butt hurt.

My mistake, I didn't realize how important you are.

Thanks for the pictures Doug. I appreciate the real world perspective. While theory is nice seeing practical applications in living color really helps and gives me hope that my project will turn out (half) as good.

Oh, and my feeling is also hurt because nobody bowed down and thanked me for my ambiguous post filled with information you didn't ask for lol.

Also, to answer your original question - you can use mild steel 2xwhatever for outriggers and utilize your MIG to tack the CM together and it won't hurt. The TIG process will use mild steel filler rod so it will be compatible for lack of better terms.

another useless statement.. what's up with the personal attacks..

Agree, another guy w/no car and who THINKS he's smarter than everyone else.....

Jeremiah, your info was useful I’m not sure why you felt as though you should’ve been included.

Doug, I greatly appreciate the pictures. If you could I would like to see pics of how it’s all laid out on the bottom side. I’m pretty sure we put the cross bars from the 2x4 box frame connectors in the floor by the rear seat but I’m almost 100% sure we didn’t do them up front. Headed out to look now.

I'm just messing with you buddy lol. Please take my middle comment with much sarcasm.

After re-looking at my setup over the weekend I am all in on the 2x3 outriggers in for the front bars. What I like about it among all the other reasons discussed is that the 2x3 is flat and level which gives you something decent to measure off of.

Another thing to note on my car is much wider at the windshield than behind the front seats. This means that the hoop is much narrower than the span across the a-pillar bars. Is there a rule pertaining to how far door bars can kick out (in degrees, looking from the top of the car) to meet the a-pillar bars? I did not find anything in the rule book but thought I'd ask here.

I assume the other body style of the era have the same issue to tackle if you want the bars tucked up good.

FastMop has some good pics too, he might post them up.

I built my chassis to cert for 7.50's. There is no ruling on angles or parallelism for the bars. Built how you want for your car, but use the required tubing measurements.

If you have any questions that are a grey area E mail your NHRA Division tech director. That's what I did. At the time Rich Bowers was our div 3 director. He answered all questions promptly. That way you know it's correct.
Doug

As long as the driver is inside of that 1.625 cage, they aren't fussy about fit when it comes to cert. Take the time to get the bars fitted out and up close to the doors and body, out of the line of sight out the windshield, etc. When you can't see the tree because of the A pillar bar, or don't fit in the car, it's too late once it's welded.

I'd have the bars come back along the top of the door then have them bend in at the hoop

After 44 years of racing and having cars certified to 7.50 I finally made the big time and have a chrome moly cage in one. Who knows what’s next for me.

I like to keep all the bars as straight as possible so
a slight angle at the main hoop will get you out to
where you need at the A pillar.. straight bars
are stronger