Thread: replacing frame rails how think should they be

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hey everyone Im replacing the rear frames rail and connecting to the front frame rails with 3x2 box tubing but i dont know how think i should get? should I get 3/16 or 1/8 the car is a 63 comet 500 hp street/strip any info would be great thanks

1/8 will be plenty, I'd be looking for thinner stuff but Shapiro Supply shows 1/8 to be the thiinest in 2x3.

I would think 1/8 would do but if you have revisions 3/16 is going to hurt you weight wise

You might want to look at possibly using say 2x2 as it will save you about 12 oz (3/4lb) per foot and gain you an inch of ground clearance--or some other variations instead of just going to 2x3--- like maybe even round 1 5/8x .083 would save 3 lbs foot

im to worry of the weight of the 2x3 the 2x3 is for the rear frame rails and I was going to use 2x2 to connect front rails to the back rails.I was going to use 14 guage sheet goods for the floor and trunk. Bother n law work a metal fab shop and he can me 24ft 2x2, 24f 2x3 and 5x10 sheet of 14 guage for $250 bucks is this a good price

you don't need anything near as heavy as 14ga. for a floor, especially if you're going to install heavy frame ties!!! I drag raced a number of Mavericks and Mustangs over the years, usually used 2 X 3 11ga. for the frame ties and 1 1/2" round tube for crossmembers, with a bit of carefully placed, welded, and gusseted 10ga to use for 4" X 4" plates where the crossmembers go in. One round tube works great as a front attach point for a set of ladder bars, and another with a bolt in center section for a transmission crossmember. As your brother-in-law works in a fab shop, some nice 20ga. with a few beads rolled in it will make a great floor, be plenty strong, and way, way lighter then a slab of 14 ga. My last Mav ran low 10's, 9's on the bottle with the same setup for floor and frame ties, plus a 10 point cage! Leave the heavy stuff for tanks, takes horsepower to move a lot of extra weight!!!

A well designed executed roll bar/cage is more a major part of the strength of the backhafted section than the thickness of the rear frame rails.

major part is right--made out of the proper materials--

he is talking about 48 feet of stuff that weighs almost 4 lbs per foot

1 5/8 x .083 weighs only 1.4 lbs ft

Go to AutoWeld web site (they are in pennsylvania in case there is more than one popping up in google) they are the folk that make most of the kits for the commercial resellers - competition engineering for example. They might make a rear frame kit for your car, they might even have an installation video of how to put the frame in that car. The tubeing will be nice and thick - an 1/8th (11ga) is too thin, even if they don't have a specific frame for that car they will have a universal kit and they offer it tacked together as well. All the engineering is done for you. They also have a cage for that car - like Gary1 said, you will need the cage assembly to tye everything together (you may not realize it as of now, but when you cut the stuff out to install the rear frame and connectors you will be cutting your car in half and replacing everything from behind the drivers' seat - it needs to be resupported and the cage is what tyes it all back together. I have done this a lot.

11 ga. does work fine, proper construction and gusseting is much more important then mass and bulk.... My last Maverick built with 11 ga. did 5 summers on the track then another 3 years on the street before I sold it. It's still alive and doing very well!

Also, I ran my frame ties half above and half below the floor with lots of weld on both sides. The stock floor is a very strong structure, designed very well with lots of bends and beads to increase it's strength. The most important part is to NOT cut everything apart at once on the car. I would suggest having the frame ties, main cage hoop, and door bars installed first. Then, brace everything thoroughly in the back half of the car laterally and longitudinally BEFORE you cut out any floor or structure to make room for the new!!!!

If you are going to continue with the leaf springs on the rear, you really don't need to do anything to that car except attack the lower traction bar to a spot thats about a foot in front of the leaf spring front hanger--In 1964 I raced a cyclone and I ran a piece of angle iron along that lowerportion of the unistructure to the mounting point

Now, if you are going to add coil overs you will need toadd strength to the upper mounting area to carry the weight ---back in those days they were running the AF/X cars with pretty much just a cross member mount in that area for the arms to hook to.

Your biggest area to work with is the front suspension on that car to make room widthwise for the engine/exhaust

Hey dave thanks on the tip on bead rolling I didnt think of that.Im going to use a thiner guage for the floors and bead roll it. hey jerry I will be useing a 4 link with coil over rear suspension or a ladder bar and coil overs because my rear tires will hit the leaf springs the tires are 28in tall by 10 wide as for the front end im puting a straight axle on the front so I wount have the shock towers nomore the engine is a 393 clevor.

That sounds like a fun build, post some pictures as you go

take a look at the welded kits that Competition Engineering has(Moroso company) all the parts fit together like they should, jig welded------------

We picked up a brand new roller from Jegs back when they had their shop.Certainly was a education just being in the shop watching them build chassis's.All the brackets being plasma computer cut on a jig for one.

The primary support is above the coilover area and forward of that.Anything that is remaining after the coilover area is just supporting the rear portion of the body.All the torque effect and instant center's from whatever traction devise you have is applied to that coilover are and needs the tie/connection of a good roll bar/cage.

I am a fan of Chris Alston's Chassisworks and their Battle Cruiser back hafts mainly because of the four link ends they offer.The durability they offer in that is hard to match.Remember when you order a roll bar/cage you get a banded pipes that need to be fish mouthed to size.It does really matter how tight those seams are.You want to fuse those pc's of pipe together and not do filler welds for gaps.So make sure you have the fixture to fish mouth.

Depending on how comfortable you are welding,you might want to work out a deal with a weld shop to tig weld it after you spot welded it together.No offense intended here.It's just I have seen a cage come apart and gin-zoo the driver.Not a pretty sight.You might want to buy a box of gussets for the joints.You wouldn't think so,but it's the little things that matter.

I look forward to your posts on the build.