2"x3" 0r 2"x4" and either 1/8" or 3/16" thickness. If going with the smaller tubing you could use the 3/16 for more strength.

Gary

 

tubing wall

Most of us use 0.120 wall tube...2x3,2x4,2x5 square main rails....0.095 or 0.120 wall for cages and hoops..Just Make it be STIFF..Safety and performance issues ya see...

OMT

 

I agree w/ OneMore - 0.120 wall rectangular tubing is more than adequate for car frames. It is the shape of the tubing, not wall thickness that gives you the strength. If you were to use a "C" channel, you would need to go to the thicker section but a closed tube is much stronger with less wall. You can eve drill large holes in one side of the tube for internal access and not lose any strength.

 

Sounding good.

The local metal shop has 2X3 and 2X4 -- 0.125 listed, so it will do just fine.

Another question.. I want to keep the original floor pans (they drop down about 6 inches below the rear seat floor, under the front seats). I would really rather not have the rails running through the inside, so what do you think bout shaping it down and under the floor pans, it will have a bunch of bends and wont be as nice as a straight rail for the middle section.

see any problems with this?

And finally, any ideas on here i can find info to draw out a frame, based on a mustang II front end? Looking at the heidts one. Where can i find info on the width of the front frame rails and such?

Thanks!
Mike

 

I have a buddy who is just finishing a '67 Falcon with a tubing 'space frame' built just as you describe. That is going to be one SUPER car - custom built front suspension, custom turned aluminum wheels, TOTALLY anal body work, racing/plush interior, monster 289. He is anal to the max about details and the car is a literal jewel. Been in progress for at least 4 years but he did have to take off quite a while to beat colon cancer but still, he is taking a really long time to do it perfectly.

 

Another question.. I want to keep the original floor pans (they drop down about 6 inches below the rear seat floor, under the front seats). I would really rather not have the rails running through the inside, so what do you think bout shaping it down and under the floor pans, it will have a bunch of bends and wont be as nice as a straight rail for the middle section.

see any problems with this?

I can think of a few...
A bunch of bends will only add flex to the rails. Every bend you make will also induce extra fatigue points into the chassis. And keep in mind these "bends" will end up being cut and welded "Z" bends. Keeping the rails straight is the best practice for stiffnes and fatigue. That's why they run through the floor. The other issue is ground clearance. If you plan on setting this car close to the ground you need to keep the frame high enough so it doesn't drag...

And finally, any ideas on here i can find info to draw out a frame, based on a mustang II front end? Looking at the heidts one. Where can i find info on the width of the front frame rails and such?
Your best bet is to measure up the car you are putting the stuff under. Use what you've got as a baseline and go from there. I don't know what the track width differences are between your '70 and a Fox Body buuuut, it may be enough to make that suspension look funny under your car... Measure the track width of the '70 and compare it to the Heidts kit.
This is a huge undertaking if you haven't done this kind of work before. I would suggest picking up some chassis design books and doing some homework before you buy anything...
Mark

 

Measure the track width of the '70 and compare it to the Heidts kit.

Mark

Well lucky for me, the car as of now already has a stock mustang II welded onto the custom frame. My reason for replacing it is:

1: The jacka$$es that built this car cut the x member to take a stock oil pan DUH, so now it is soooo weak.

2: i don't trust their welds onto the frame, look pretty sketchy, Id be alot happier with my own welds.

Keeping the rails straight is the best practice for stiffnes and fatigue.

On that note, where is the best place to put a jog to line up the track of the front IFS and the mounts for the rear end, im guessing as of now, it wont all be completely in-line (im thinking 4 link for the back, ford 9").


And finally, about books, any references, i've looked around but have yet to find anything that sounds like a bible of chassis design?

Thanks, you are all a wealth of info, couldn't do any of this without you!
Mike

 

Just do a google under chassis design. You'll find tons of info.
Here is a site that has a bunch of stuff and a lot of it is usable...
http://www.gmecca.com/byorc/designpublicationsbooks.html
You really need to have a good understanding of the terms, hows and whys when reading many of these books. Don't expect to pick one up and run with it... you'll be a while just getting a grasp of the basics.
Mark

 

Take a good long look at drag car designs. You want to adapt and stiffen from there for your purposes. Floors will become secondary when you design and build your own framerails. Form must follow function. Plan on at least some sort of roll bar or cage as you will no longer have the designed-in stiffness of the unibody to build from. Look into getting some mandrel bent rails or even some individual bends of 2x3 and use them like building headers. The difference being to use some inner supports and rosette welds to hold it all together. You'll be so happy you did when you step back and look at it.

 

Look into getting some mandrel bent rails or even some individual bends of 2x3 and use them like building headers.

I've been wondering about this actually.. I can get this done, i know where to get it done, and can probably afford to. But is it actually worth it? Wouldnt bending just stretch the metal on one side and in turn weaken it? uin theory if i weld Z's for the frame properly,l it should be as strong as the original metal.. If i hold it in place well and make sure it doesnt warp, it should be just as good?

 

Speedway has mandrel bent chassis kits here and here and here

 

Reproduction 32-34 Ford fames are built up from 3/16" flat sheet. The sides are cut from the flat sheet and placed in a jig that forms them to the shape of the original frame. Then flat sheet steel sides are full welded on. After all the crossmembers and X frame is welded in the frame is flipped upside down and the bottom sheet steel is welded on forming a completely boxed frame which is super strong. My frame from The Roadster Shop is a work of art, it has some of the most perfect TIG welding I have ever seen. If it would not rust I would like to have left it in original metal rather than painting it.

Vince

 

My plan was to do something like this

Cboy's Frame

I like the way it came out.. and seems fairly straightforward?? A frame designed like this should be plenty strong shouldnt it?

Mike

 

Has been done probably 1,000,000 times and yes, is very strong.

 

Keep it simple

When one looks at a sprint car or a dragster there is nothing there that does not absolutely needs to be there..No unessasarybends or joints anywhere..

Go Here as they have extensive online tech articles on squaring a chassis as well as a lot of suitable parts at decent prices..

As far as mandrel bending versus cutting and welding Z's it is either your money or your time deal..either one works just fine..Just a lot easier and a time saver to pickup some prebent frame rails..

OMT

 

BTW, most frame builders recommend 2" x 3" tubing for street use with a rollcage and 2" x 4" for street use without a cage...

Russ

 

I guess my point about mandrel bent rails is regarding appearence as well as strength. If I had my choice, even if I was butting together with bends, I would design my frame to be bent in load areas vs being simply welded. While welding is a wonderful and sturdy process it does do things to mild steel that over time will prolly result in a failure...minor or major.

To expand that thought...let's call it the kick-up where it goes over the rear axle. I would design it to be bent, 1 piece per side, as long a peice as possible, then add my length front and rear from there. All of the butted joints would have inside plates to carry the added tubing rosette welded in place on both sides, fully welded joint, then metal finished in all visable areas. I'm pretty sure that would be a real strong and durable frame rail. I guess 'cuz I've done it to a few already. Once you get one lined up where you like it, before welding it all up you duplicate exactly for the other side and presto, 2 custom built mandrel bent rails.

I will not discount the fact that many rides are out there with "Z'd" rails and they work. But no matter what happens to the steel in a bending process, 1 piece is better than 2. And indeed the tensile strength of the steel may be greater in the bent area due to the process. I aint no metalurgist, just goin on regular knowledge there. Why not just butt weld and miter cut roll cage tubing? 'Cuz it's the same deal, more integrity with 1 piece where a change in direction is needed.

I hope I cleared up my input there fellas.

On a totally different note I wonder if my new avatar is up yet...

 

In my 78 camaro Im going to put in sub-frame connectors to my mid cross-member im making then from there back 2x4x.188 wall tubing. Granted it will be both street and drag but I like over kill when theres rust especially. Im making the sub-frame connectors out of 2x3x.188 tubing. I would put in torque boxes too. if the 351 is or will be a hot engine. I have twisted one unibody already. almost forgot any miter cuts you have before the rear axle make sure you drill holes in the joint around the area to be welded and put a plate in there that you can weld thru the holes connecting the miter on both sides, butt weld with backing and plugs too, Ive been told you shouldnt do this past the axle since its a crumple zone but i guess its up to you.