Converting Unibody 4th gen to Solid Frame?
Staging Lane
Joined: Jul 2008
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I was checking some prices and round tube over 4" really jumps up in price.
Now I understand why most folks use rectangular tubing if possible.
I don't have a way to measure the exact size I'm going to need, but if I went with a 4x2, 4x3 or 4x4 tube, would .125 wall be strong enough? I know it's stronger that what the factory used and the convertible cars seem ok. I figure this will be strong enough. I want it to be light, but not too light. Know what I mean? I'd rather err on the side of caution and have a few extra pounds than have the car be a flexi flier.
Now I understand why most folks use rectangular tubing if possible.
I don't have a way to measure the exact size I'm going to need, but if I went with a 4x2, 4x3 or 4x4 tube, would .125 wall be strong enough? I know it's stronger that what the factory used and the convertible cars seem ok. I figure this will be strong enough. I want it to be light, but not too light. Know what I mean? I'd rather err on the side of caution and have a few extra pounds than have the car be a flexi flier.
Thread Starter
Joined: Sep 2004
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From: Hou. TX.
Yep. If we forget the trans tunnel for a moment, the area under the doors is going to be the weakest part of the frame. See the frame in post #50. If it's not beefy there, the car will want to droop and flex there. I want the points between the four spring/shock mounts to be as rigid as possible so the suspension works like it supposed to and bumps don't cause the chassis to flex.
Once you get bigger than 2x4 tubing, 1/8" wall looks to be the thinnest there is. I'm comparing weights as well.
2x4 .083 wall is 3.24lbs per foot
2x4 .120 4.75
4x3 .120 5.61
4x4 .120 6.53
4" round .125 5.1
It looks like each side will need to be 5' long, so that's 10' total. So even the beefy 4x4 would weigh 33lbs per side. 66lbs total. That's not too bad considering that's the weakest area.
Does anyone make a 4x4 with a thinner wall?
Ahh, here's a thought. I could take 20' of 2x4 .083 tubing and lay them side by side. Then cut the 4" tall side off of just one length so it's a C shape. Then I can weld them together to make a 4x4 piece with an extra wall in the center. Both sides would weigh less than 66lbs and still be plenty strong.
Anyway, the rest of the car will use smaller, lighter tubing since it can be cross braced.
Once you get bigger than 2x4 tubing, 1/8" wall looks to be the thinnest there is. I'm comparing weights as well.
2x4 .083 wall is 3.24lbs per foot
2x4 .120 4.75
4x3 .120 5.61
4x4 .120 6.53
4" round .125 5.1
It looks like each side will need to be 5' long, so that's 10' total. So even the beefy 4x4 would weigh 33lbs per side. 66lbs total. That's not too bad considering that's the weakest area.
Does anyone make a 4x4 with a thinner wall?
Ahh, here's a thought. I could take 20' of 2x4 .083 tubing and lay them side by side. Then cut the 4" tall side off of just one length so it's a C shape. Then I can weld them together to make a 4x4 piece with an extra wall in the center. Both sides would weigh less than 66lbs and still be plenty strong.
Anyway, the rest of the car will use smaller, lighter tubing since it can be cross braced.
Last edited by JasonWW; Dec 9, 2008 at 04:40 AM.
Thread Starter
Joined: Sep 2004
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From: Hou. TX.
No, not really. I work 6 days a week so Im working on it in my spare time. It's going to be slow because this is the first big project like this I've done. There is a big learning curve involved.
I may do such a sucky job I'll have to scrap this chassis and buy another stripped one and start all over. The main thing is I plan to learn a lot.
I may do such a sucky job I'll have to scrap this chassis and buy another stripped one and start all over.
The main thing is I plan to learn a lot. Last edited by JasonWW; Dec 9, 2008 at 09:23 PM.
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your brave man, but try it. All you have to think is its just steel. You can fix it. You have exellent ideas.
I would go with the 4x2 .083 wall and dont even worry about doubling it.
Angle cuts will be alot easier with the rectangle tubing. I wouldn't worry too much about support in the trans tunnel. I would do the tubing like above with an X in the middle. Cut holes in the x to run your pipes through. Then the trans tunnel is not as involved in the frame design.
Like in the picture below, but your own design in the front and in the rear.
I would go with the 4x2 .083 wall and dont even worry about doubling it.
Angle cuts will be alot easier with the rectangle tubing. I wouldn't worry too much about support in the trans tunnel. I would do the tubing like above with an X in the middle. Cut holes in the x to run your pipes through. Then the trans tunnel is not as involved in the frame design.
Like in the picture below, but your own design in the front and in the rear.
Thread Starter
Joined: Sep 2004
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From: Hou. TX.
Thanks for the tips. So your saying I should do it like in post #1?
One thing is that there won't be room under the seats for the exhaust. I plan to tweak some C5 headers and run twin pipes under the driveshaft.
I don't even know if I'll have room under the floor for an X shape. Remember that this car is going to be really low. I may have to drop the seats a tad for the choptop.
One thing is that there won't be room under the seats for the exhaust. I plan to tweak some C5 headers and run twin pipes under the driveshaft.
I don't even know if I'll have room under the floor for an X shape. Remember that this car is going to be really low. I may have to drop the seats a tad for the choptop.
Last edited by JasonWW; Dec 9, 2008 at 11:55 PM.
Yep. If we forget the trans tunnel for a moment, the area under the doors is going to be the weakest part of the frame. See the frame in post #50. If it's not beefy there, the car will want to droop and flex there. I want the points between the four spring/shock mounts to be as rigid as possible so the suspension works like it supposed to and bumps don't cause the chassis to flex.
You would probably be best off running an X of some sort and running the exhaust through the rockers like you mentioned before. then the tunnel doesn't have to be wider to accommodate exhaust, it doesn't push the seats out farther and you don't compromise being able to lay the frame on the ground.
As you mentioned before you can make any space an airtank.
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Verdad Gallardo TECH Fanatic
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So you are going to drop the floor between the frame rails? Hmmm. If thats the case, ill have to think about how to do this. Your idea might be pretty good with the exhaust under the driveshaft. You will still have to have some kind of cross bracing for the frame rails though.
Thread Starter
Joined: Sep 2004
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From: Hou. TX.
Lately I've been thinking about making the choptop even more extreme. Give it a real gangsta look, something like Darth Vader would have built. Or maybe the Prince of Darkness would drive around in. Something that's going to scare people. 
Oh yeah, even with my *** sitting so low, I'll still have room across the rear of the seat as well as in front of it. I just can't have any tall crossmembers right under the seat.
Oh yeah, even with my *** sitting so low, I'll still have room across the rear of the seat as well as in front of it. I just can't have any tall crossmembers right under the seat.
Last edited by JasonWW; Dec 11, 2008 at 12:25 AM.
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ok i got it now. Well, dont worry about having to run your exhaust under the members. Just cut a circle through the crossmember and weld a piece of pipe in there. That way you can run your exhaust through it. Ever since I saw this thread I have been thinking about how to pull this off.
I would gut a f-body (like you are doing), nothing left but the sheetmetal. Brace up the inside of the body as well as possible. Then cut the whole floor out of the car. Once the floor is cut, you can set the body over the chassis to the height you want. Make yourself some temporary body mounts to hold it where it needs to be, and start building your floor.
I would set the body so the bottom of it is level with the bottom of the frame rail. Build the floor keeping everything as tight to the chassis as possible. I dont think you would have to go through all that of dropping the floor between the frame rails. You can gain alot of room by basically using a cushion directly on the floor.
Once you have your floor finished, and seat height figured out, then you can look at the top and see how much you can chop off of it before it hits your head.
That brought something else to mind though. How tall are you? because sitting that low in these cars, might keep you from seeing out the windshield. im almost 6', and i dont think I would be able to see if I was sitting on the floor of my car.
Then finish up your floor and start putting the car back together. Done!! sounds simple right?
I would gut a f-body (like you are doing), nothing left but the sheetmetal. Brace up the inside of the body as well as possible. Then cut the whole floor out of the car. Once the floor is cut, you can set the body over the chassis to the height you want. Make yourself some temporary body mounts to hold it where it needs to be, and start building your floor.
I would set the body so the bottom of it is level with the bottom of the frame rail. Build the floor keeping everything as tight to the chassis as possible. I dont think you would have to go through all that of dropping the floor between the frame rails. You can gain alot of room by basically using a cushion directly on the floor.
Once you have your floor finished, and seat height figured out, then you can look at the top and see how much you can chop off of it before it hits your head.
That brought something else to mind though. How tall are you? because sitting that low in these cars, might keep you from seeing out the windshield. im almost 6', and i dont think I would be able to see if I was sitting on the floor of my car.
Then finish up your floor and start putting the car back together. Done!! sounds simple right?
Thread Starter
Joined: Sep 2004
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From: Hou. TX.
Well your side frame rails are going to have to neatly integrate into your existing "siderails". If you don't have to raise the transmission tunnel, it makes sense to keep it and just cut out the floor under each seating position.
I still want to install each siderail and then I can set the body and rails right onto a flat surface. From then on I know exactly how low everything can fit. It's a little messed up, I know.
Right now I'm considering ditching all the rear sheetmetal from the door jams back and making a one piece tilt rear end of fiberglass.
I still want to install each siderail and then I can set the body and rails right onto a flat surface. From then on I know exactly how low everything can fit. It's a little messed up, I know.
Right now I'm considering ditching all the rear sheetmetal from the door jams back and making a one piece tilt rear end of fiberglass.
Last edited by JasonWW; Dec 15, 2008 at 12:18 AM.
Thread Starter
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From: Hou. TX.
I have been toying with the idea of making the doors fixed. The car will be so low that it would be pretty easy to just step over the door and drop down into the seat.
Think of Micheal Keatons Batmobile or the Sterling kitcar. Maybe even a gullwing affair consisting of the side windows and roof. I can just hop in it.
None of those really floats my boat right now.
Sterling:
Here's a really ugly car, but notice the gullwings? Now imagine if they were motorized and went all the way vertical plus my much shorter windows were attached. The short windows would keep you from hitting your head on them. Eh... It's a thought.
Think of Micheal Keatons Batmobile or the Sterling kitcar. Maybe even a gullwing affair consisting of the side windows and roof. I can just hop in it.
None of those really floats my boat right now.
Sterling:
Here's a really ugly car, but notice the gullwings? Now imagine if they were motorized and went all the way vertical plus my much shorter windows were attached. The short windows would keep you from hitting your head on them. Eh... It's a thought.
Last edited by JasonWW; Dec 15, 2008 at 08:57 AM.
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From: 336 NC
Just trying to imagine and give ideas. How about cutting the oe floor up the center from front to rear. Taking the two sections, and pulling them out. Then you'll have a open center of the car to make frame rails against the backs of the rockers and tie them into the original unibody/subframes. They'll be like jacking rails or a perimiter frame almost. Then run another set of rails along the center forming a transmission tunnel. You could the add braces between the sets of rails to further reduce flex by tieing it all together. After that modify the original floor to fit and weld back in. A roll cage would have near infinite ways to tie in.
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From: 336 NC
When I say the back of the rocker panels I mean have the frame rail out against them like a corvette. And if none of the unibody is going to be left cut the firewall, floor, strut towers, and whatever else out to mount the shell on a race chassis. But I thought this thread was ideas on how to make the existing car into a full frame car. My idea from before would tie everything together into one.
Thread Starter
Joined: Sep 2004
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From: Hou. TX.
Your idea from before may be perfect, if I understood it. I don't.
I originally started this thread with the intention of just redoing the front suspension. Then I said "Hey, why not extend it back a little more?". Now it's gone full blown tube frame and possibly mid-engined. Things just have a way of changing.
I originally started this thread with the intention of just redoing the front suspension. Then I said "Hey, why not extend it back a little more?". Now it's gone full blown tube frame and possibly mid-engined. Things just have a way of changing.
Last edited by JasonWW; Dec 16, 2008 at 05:57 AM.
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SuperSports idea is basically the same as mine. Use the stock unibody structure to keep everything square. Brace up the car from front to rear very well, as well as side to side. Cut out the entire floor from the firewall back to wherever the body ties back into the rear subframe.
Then you can build your whole frame onto the car. I dont think another set of rails is necessary in the middle, but might work well if you cant use material of any height where the seats go. Then build a simple floor from scratch. Its not that difficult at all really. You can buy prebent tunnels, or just bend one over an argon bottle or even a tree works. You wont need molded carpet or any of that mess either.
How does the car look now? any progress?
Then you can build your whole frame onto the car. I dont think another set of rails is necessary in the middle, but might work well if you cant use material of any height where the seats go. Then build a simple floor from scratch. Its not that difficult at all really. You can buy prebent tunnels, or just bend one over an argon bottle or even a tree works. You wont need molded carpet or any of that mess either.
How does the car look now? any progress?