What to make my frame out of??? Round or rectangle?

[Black Rock Fab]

Hey guys, im not looking to get into what is stronger conversation (tube v.s rectangle ) but i have been doing a ton of research and am trying to decided what type of frame to build for my pro touring project. Just a little insight if you have seen the movie Christine then you know the car im building. I have a 1958 Plymouth Belvedere that im installing a 6.1L heim with superchager pushing 550hp with front and rear c5/c6 suspension. Im at the point where im deciding how to build the frame. should i do the standard 4x3 or do something different like the guys at SIII and use some 2" x .120 or .188 wall tube? what do you guys think? i attached some pics of the original frame. . . . . . . kinda funny some guy tried grafting a nova front clip. . . . .scary!!!!!!

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75908

amazing their is nothing to these frames!!!!!! ! ! ! !! ! ! ! !

[Black Rock Fab]

75909

this is the frame i was referring to with the tube. I not a fan of how they did the upper A arm mount on the front, doesnt seem like alot of support

[T_Raven]

I just built a frame table to put my 67 on. I've got some 2"x4" tubing that I'll probably make the sub frame out of. I've always liked the idea of round tube though. I just got a tubing bender so I'll do some serious thinking about whether to use round or rectangular. I'm interested in seeing everyone's responses.

[Black Rock Fab]

T raven, what bender you have? I have a JD2 but i made a hydraulic setup for it which makes it really nice. I want to be different and go crazy with the tube. I would really like to hear from some people that have built or had both so im excited to see what kinda thread this will turn into. thanks kyle

[Black Rock Fab]

Also another question. Should i use the original aluminum sub frame for the IRS and IFS? I wasn't planning on it but i have seen them used in a few builds and it does give it a clean look i think. But then again i like the idea of integrating the mounts into the frame. Just thoughts.

[T_Raven]

I bought a JD2 32. I also bought a Harbor Freight tubing roller. I'm going to set them both up on a cart with an air operated ram like these plans on ebay

http://www.ebay.com/itm/Air-hydraulic-bender-frame-PLANS-JD2-tubing-bender-HF-tubing-roller-/261156249089?pt=LH_DefaultDomain_0&hash=item3cce201e01

[Black Rock Fab]

Very nice. Much better than doing It by hand. Ill take some pics of mine tomrrow. I have this digital read out display also called tube bandit, but they have gone under since I bought it.

Anyone have any input on the frame type?

[astroracer]

Anyone have any input on the frame type?

I guess it really comes down to how much work YOU want to put into it. A twin round tube frame is a lot more fab intensive then rectangular tube and it will take a lot more design time. The round tube does look cooler but is it worth the time and effort to build something like that to put under a big heavy car that, if you keep it low, no one will ever see...
I am in the bubble up/thinking/sketching phase of a twin round tube frame for my Model A. Being that most of the heavy design work on the van is done my mind starts to wander so, if you decide to go round, I'll be watching. :)
Just some suggestions to get you thinking.
Start sketching the side view profile of your round tube frame. Use the current CLR of your available bending dies to set up matching radii for your parallel tubes. I am starting out with a 1 5/8" lower tube and a 1 1/4" upper tube. With my current dies, to get the bends to follow (parallel to) one another, the finshed rail height will be 4.81". With a 6" CLR for my lower 1 5/8th dia. tube (using that as a constant throughout the length) I am finding I will need a large radius bender to make "matching" bends in the upper tube that flow with the lower tube. My top tube is 1 1/4 inch so any inside bends will work with my current 3" CLR Die. THe "outside" bends will need an 8 3/8ths CLR to match and flow with the 6" radius of the 1 5/8 tube.
There are some things to think about when going this route, maybe we can help each other out.
I just ordered those bender stand plans off Evil bay.. :)
Mark

[Black Rock Fab]

Hey Mark,

Sorry for slow response. Been crazy busy at the day job. Yea i know what your saying with all the extra work but im at the point where its do or die lol. I have done enough tube work to give it a go i think. I understand what your saying with the bend center line. I still need to grab some pics of my bender. Im thinking of doing 2inch x .120 wall and some 1 3/4 and maybe run another 1 3/4 or 1 1/4 to run brake lines and wires down inside jsut some ideas. I hope to be picking up my corvette suspension in a few weeks got some customer catching up on bills this week!!! Feels good to get paid for parts shipped hahah anyone else have some input?? thanks kyle

[sccacuda]

The square tube is relatively idiot prove. It would be in a ladder config, which is strong, but still has torsional flex. An 8 point would help reduce that. A round tube really requires some engineering to be strong and torsionally stiff. The only advantage is weight. It can be made more torsionally stiff than a ladder square tube, with the proper engineering. I prefer a square tube chassis like the Trans Am series car from the 90's. They are relatively light, torsionally stiff, and super strong. Most road race chassis's start on square tube rails with tubing for structure and support.

[Black Rock Fab]

Craig, so what do you think of the above tube frame design? what sizes and design would you suggest i consider for my project? thanks kyle

[Schwartz Performance]

Round does look cool, but also think about the weight aspect. Yes you'll spend a ton of time notching tubes compared to making it out of rectangular. You can also make it out of partial round tube, like we do on our chassis. (Front crossmember, rear upper 4 link mounts etc).
Material costs will probably be higher too, as you'll use a lot of round tubing.

Regarding the aluminum subframes- Might want to try and test-fit the 6.1L into the front sub- My guess is you won't be able to get it to fit right UNLESS maybe you cut the firewall- The engine in C5/6 sits pretty much behind the centerline of the front wheels. Using the rear sub might be pretty cool, however!

Good luck :)

-Dale

[Black Rock Fab]

Dale, thanks alot for that input you do some amazing work!!

I have no real concerns with the price and notching aspect of tube work. I deal alot with DOM for the monster trucks so i get good pricing.

Dale do you guys bend your own rectangle main frame rails?

As with the aluminum factory sub frame for the suspension i see what your saying with the 6.1 fitting but is it due to the sub shape or the rack being so far back? If i mill a new steering arm moving the rack forward you think that will allow me to slide the engine forward? or is the sub frame that confining? I should be picking up the front and rear stuff soon. So i can get a better understanding of the fitment

thanks kyle

[sccacuda]

Craig, so what do you think of the above tube frame design? what sizes and design would you suggest i consider for my project? thanks kyle

It looks cool, but I don't know who made it or engineered it. I personally would recommend a square tube box frame, 2x4 mild steel .120 wall with cage if your building it yourself. Their are a few companies on the forum that can mandrel bend your square tube rails. You can't go wrong with anything Schwartz recommends, this is what they do.

[astroracer]

If i mill a new steering arm moving the rack forward you think that will allow me to slide the engine forward?

You don't want to start chasing that tail... Changing the rack location destroys all of the inherent Corvette steering geometry. If you are going to do that you should start from a clean sheet of paper and forget the C5 subframe.

[Black Rock Fab]

It looks cool, but I don't know who made it or engineered it. I personally would recommend a square tube box frame, 2x4 mild steel .120 wall with cage if your building it yourself. Their are a few companies on the forum that can mandrel bend your square tube rails. You can't go wrong with anything Schwartz recommends, this is what they do.


I want to stay away from a cage in it just so it doesn't clutter the interior. Thank you for the input keep it coming. I still have some time before i start building the frame. Just picked up a 4ftx12ft old tslot table from a mill so i can build the frame on it. So another week or so i want to have a decision made on round or square. It just seems it all comes down to the time rectangle saves v.s bending the tube in 3planes keep it all the same, which some of the monster truck frame building i was involved with we have done. thanks kyle

[Black Rock Fab]

You don't want to start chasing that tail... Changing the rack location destroys all of the inherent Corvette steering geometry. If you are going to do that you should start from a clean sheet of paper and forget the C5 subframe.

I see alot of people making the arms moving it forward but if i recall none of them use the factory sub frame.

Im not opposed to just building my own mounts i just happen to see a corvette build that narrowed them to fit that app and it just looked clean.

[sccacuda]

You don't want to start chasing that tail... Changing the rack location destroys all of the inherent Corvette steering geometry. If you are going to do that you should start from a clean sheet of paper and forget the C5 subframe.

Could he move the rack down and use a longer pin to put bump steer shims in?

[Black Rock Fab]

I mean i would really like not to cut my firewall up but having the engine back further would really help with weight distribution. I plan on have air ride on it too so that's more weight in the back

[astroracer]

Could he move the rack down and use a longer pin to put bump steer shims in?

I won't recommend moving ANY of the steering components from the initial design points. ANY movement will alter the relationship between the components and this pretty much makes using a "Corvette" suspension a moot point. This applies to any front suspension, not just a Vette. If you have to start moving things you are much better off redesigning all of the suspension points to work with the new layout. Start with the Corvette rack, put it where you need it to be and then redesign the control arms and steering geometry to work with that position. This is the only way to get it right.

[sccacuda]

I won't recommend moving ANY of the steering components from the initial design points. ANY movement will alter the relationship between the components and this pretty much makes using a "Corvette" suspension a moot point. This applies to any front suspension, not just a Vette. If you have to start moving things you are much better off redesigning all of the suspension points to work with the new layout. Start with the Corvette rack, put it where you need it to be and then redesign the control arms and steering geometry to work with that position. This is the only way to get it right.

Easy for you, you do that for a living!! Just for a general question, if that route is not feasible, and like most everyone else here that builds what is available, do you have any suggestions?

I have moved the racks before, and then adjusted pickup points and tie rod length to eliminate bump steer. I use a Hunter DSP 600 alignment machine. I remove the springs and with the heads attached, move the suspension through its arc and shim accordingly to eliminate bump steer (dynamic toe) and even adjust toe cut at full turn to be the same as stock. I guess I don't understand how the rack affects suspension geometry if the rack isn't influencing toe any differently than the stock setup.

[Black Rock Fab]

Keep it going guys with the steering discussion. .. . i need to read more and do more homework on my suspension theories but i kinda see what Craig is saying. If your just moving the rack down how is it effecting anything through the suspension travel? Your not moving it away from the center line of the suspension.

I just want to bring up another point with the style of frame. I have also seen alot of guys cutting flat plate and boxing it in and welding all the seams. whats everyone thoughts on this? besides all the grinding and flapper wheeling. I like the look of the sharp corners and you can really have the frame how ever you want. Specially since i have a cnc plasma in my barn!! haha that was mean i apologize

[astroracer]

Easy for you, you do that for a living!! Just for a general question, if that route is not feasible, and like most everyone else here that builds what is available, do you have any suggestions?

I have moved the racks before, and then adjusted pickup points and tie rod length to eliminate bump steer. I use a Hunter DSP 600 alignment machine. I remove the springs and with the heads attached, move the suspension through its arc and shim accordingly to eliminate bump steer (dynamic toe) and even adjust toe cut at full turn to be the same as stock. I guess I don't understand how the rack affects suspension geometry if the rack isn't influencing toe any differently than the stock setup.

No, Craig, it's not easy... and that's the issue. I know everyone has Hunter DSP 600 Alignment Machines sitting in their shop so, moving racks, adjusting bump steer, tie rod lengths and toe cut at full lock isn't rocket science to anyone on this board. What everyone has to realize is, the rack is central to a good functioning suspension design. The inner tie rod points have a definitive relationship to the upper and lower control arms, both vertically and horizontally. Moving the rack, in relation to these points in ANY direction, results in exactly what you are doing with your Hunter DSP 600. Throwing shims and longer tie rods and out of spec adjustments at a non optimized rack location to get the steering back to some semblance of what the rack would do in it's stock location with no shims or long tie rods or out of spec adjustments.
I think you understand what is going on for the most part but, this is not to be taken lightly, simply moving a steering rack willy-nilly or, even worse, using one out of an entirely different car is not good design practice and, for the most part will result in an evil handling rig that will scare the be-jesus out of you every time you hit a bump or turn into a hard corner.
Yea, I do this for a living and I want anyone reading this thread to know it is very important to get this right... Your life and the lives of your passengers and bystanders depend on YOU being able to affectively control your car...
Mark

[Black Rock Fab]

No, Craig, it's not easy... and that's the issue. I know everyone has Hunter DSP 600 Alignment Machines sitting in their shop so, moving racks, adjusting bump steer, tie rod lengths and toe cut at full lock isn't rocket science to anyone on this board. What everyone has to realize is, the rack is central to a good functioning suspension design. The inner tie rod points have a definitive relationship to the upper and lower control arms, both vertically and horizontally. Moving the rack, in relation to these points in ANY direction, results in exactly what you are doing with your Hunter DSP 600. Throwing shims and longer tie rods and out of spec adjustments at a non optimized rack location to get the steering back to some semblance of what the rack would do in it's stock location with no shims or long tie rods or out of spec adjustments.
I think you understand what is going on for the most part but, this is not to be taken lightly, simply moving a steering rack willy-nilly or, even worse, using one out of an entirely different car is not good design practice and, for the most part will result in an evil handling rig that will scare the be-jesus out of you every time you hit a bump or turn into a hard corner.
Yea, I do this for a living and I want anyone reading this thread to know it is very important to get this right... Your life and the lives of your passengers and bystanders depend on YOU being able to affectively control your car...
Mark

Mark, you couldn't be more correct!! I thank you for the input. I am one that doesn't cut corners and i want to do it right. What do you think i should do? I have all the capability to make an entire new front suspension, including new arms and cradle to fit my needs. I would rather have the engine forward more than back. What do you think? I trying to buy software from auto-ware to help with the suspension design points. thanks kyle

[astroracer]

Thanks Kyle,
As far as what you are doing is concerned I would suggest sticking with the Nova front sub and building off that. The Nova/F Body front suspensions have tons of aftermarket support and can be made to handle very well. Put in a new steering box from AFR and enjoy the ride and drive with no worries.
If you want to go full tube frame, transfer all of the pickup points to your design and keep with the known geometry. It can be adjusted a bit so you can look into that also.
Mark

[Black Rock Fab]

So you think the nova front end is better than a c5/c6 suspension? im also looking to do rear c5/c6 suspension.

[Black Rock Fab]

also, what are thoughts on frames i seen made from plates welded together to make a rectangle?

[astroracer]

So you think the nova front end is better than a c5/c6 suspension? im also looking to do rear c5/c6 suspension.
It is better because you don't have to move anything to fit the engine in. The steering box is a known factor and there is no need to move it. I would use that, anyday, over a cobbled up C5 with a non-stock rack position. Once you start modifying the C5 components any known "handling" and performance factors go right out the window.
On the Bad Ast build I started with the Corvette inner tierod points and designed the suspension around those... No compromizes.
Mark

[astroracer]

also, what are thoughts on frames i seen made from plates welded together to make a rectangle?

This is just my experience with this type of frame.... Sometimes this is done to creat an Engineering Developement Vehicle here at work. It is not widely cared for but timelines need to be met and, if this is the only way to do it, it gets done. These "plate & weld" frames are never run through any durability tests. The construction doesn't have the cross-sectional strength of a stamped "C" section or rectangular tube... All of that welding also lowers the strength of the steel plate. You would do well to just go with rectangular tubing from a strength and durability stand point. If you want sharp corners throw some All-Metal on the corners and sand it sharp.
I'm sorry if I sound negative all the time. I know what I know and I try to convey that whenever a question is asked...
Mark

[Black Rock Fab]

Mark, your not negative at all. When i see you responded i get excited, cause i know how much knowledge you have . I ordered a suspension software today so i can tweak the c6 suspension to fit my app. With some thinking im going to keep the rack where it belongs and just slide the motor back. I want the fire wall to be smooth anyway why not just cut it to make room for motor.Now you said it before if i did want to move the rack then i would have to design the suspension around that. If i do decided to do that at least i have the software to help me with that. Now with the other company's that move the rack is probably why they wont sell you the arm.. makes sense now . Now let me ask you what are some good numbers i should be shooting for when messing with the software? such as:

camber gain of .6 degrees per inch and keep the roll center movement as minimal as possible (2" or less would be good). The static roll center height should be low the ground, about 4" or so. How much should i shorten the SVSA for anti-dive?

Got a few suspension engineering books i have been reading. this stuff brings me back to the old class rooms days lol

Also, i know your not fond of it but i think im going to do a tube frame all 1 3/4x .120 wall dom tube.

Please don't take it that im not taking your advice, just need to see where im coming from. I build alot of parts deal with alot of tube work and i like the challenge.

thanks kyle

[Black Rock Fab]

This is just my experience with this type of frame.... Sometimes this is done to creat an Engineering Developement Vehicle here at work. It is not widely cared for but timelines need to be met and, if this is the only way to do it, it gets done. These "plate & weld" frames are never run through any durability tests. The construction doesn't have the cross-sectional strength of a stamped "C" section or rectangular tube... All of that welding also lowers the strength of the steel plate. You would do well to just go with rectangular tubing from a strength and durability stand point. If you want sharp corners throw some All-Metal on the corners and sand it sharp.
I'm sorry if I sound negative all the time. I know what I know and I try to convey that whenever a question is asked...
Mark

Yea finda figured. I really don't like the idea plus i mean keeping that frame together and in place while welding has to be a pain.