i have an 85 firebird an i want to know the strongest sub frame connectors that are avaliable and where to find them at and the price if you can get all of that information right now i am looking at these on http://www.umiperformance.com/2400.aspx
what do you guys think

 

those are bad @ss. although I do not know about any of the other brands.

I did my homework as far as weld points and the way it ties into the rear suspension and the umi-connectors made a huge difference in my t-top car.

 

Those have to be the best design ive seen for are cars. And the price is even better. Very well designed and not cheap to make like some others ive seen. They will go up up in price, if i didnt have a set off Hotchkiss i would be looking into s set of those.

 

i have the hotchkis subframe connectors and im happy with them

 

Yeah the Hotchkis work great! There a good design as well. Like any other, they really need to be welded in. And a long the pinch weld. I wouldnt remove them to install another set.

I just had them welded in recently. The car is so tight now, i dont feel any flex what so ever.

Going down the road i can pull the wheel to the left and right. The body feels so tight, now. It was good before because its a hardtop. But this is a solid feel that wasnt there before the install.

And when i nail it from a stop it doesnt feel like the car is going to twist in half. goes straight.

 

Square tube is not as strong as round tube # for #. This is an undesputable and easily researched fact.

Square tube is rigid in torsional applications until it twists and the torsion stability flexes. Tubular is much stronger for torsion AND twist loads.

you chassis twists, and so will these when installed onto it.the design does not link the left side to the right side to keep the floorpan in torsion sync when road forces are applied. So when the front of the car twists and the rear of the car stays flat, the square tube SFC's will twist also.

 

two examples of how square tubing twists- tubular does not do this.

 

That all sounds good and well, Ive read alot about the square versus round tube thing. I know some race cars have round tube.

But.. in the real world driving my IROC down a fast twisty road. Or the 1/4 once in a while, i doubt i would ever know if my subrames are round or square.

 

I certainly would know the difference from seat of the pants feel. If your chassis is twisting, then your car is suffering in cornering abitly because your wheels are not all staying planted. Youare driving around a corner on a tripod.

Front of the car chassis= green

rear of the car chassis = blue

sq sfc's= red

Someone sould email UMI and tell them to read this post. They need to take down their "strongest SFC's" ad. They are misleading the public.

 

I went with Spohn SFCs. I like the way they tied to the cross member area. Not sure if they sell that style anymore. The pics on their website don't show the additional supports mine came with.

They seriously tightened up my T-top car.

 

Thunderfest..There isnt much to the floor pans on these cars. IM no chassis guy. But welding a round tube to the floor pan. versus a square one. Is not going to make much difference in this type of application. None that i could tell anyways.

Where talking about weld in subframes. For a fbody that the average joe wants to play with. Not a full on race car.

Sometimes it comes down to how easy they can be manufactured. The profit margin...

 

Another added benefit for using SFC's is a jacking point so you do not harm the subframe of a 3rd gen.

Round tube is better here also.
The round tube pivots and stays within the tabs of most floor jacks .

 

Thats not the point. The POINT of this topic was "Strongest SFC's" and they are not. Spohns tubular ones are stronger keeping the chassis stiff from twisting and keeping the wheel planted and under traction around corners. Your car is still twisting like the second sketch I drew. If you can't understand this then I don't know what else to tell you. You can in fact feel the difference and experience it if you are trying to corner fast even on a street car.

Tubular is better than boxed for lightness and function. Handling boils down to one simple basic- Keeping the chassis as stiff as possible so it does not twist or flex.

and by the way, I am a chassis guy.

 

For me...The point is real world...Not to hard to understand. All that square versus round does not apply here IMO.

The part about jacking the car up is pretty funny. The jack pad is the pivot point. Mine is.


Round tube is great IM sure Spohn is a great design. Had i bought a set, and installed them, im sure i would have been just as happy.

 

I have said all anyone could say here, either you get it, or you don't. All the info is there for REAL WORLD testing and viewing.

Thank you, I am finished here. Anything else is just bickering needlessly.

 

dude why are frames square or c channel and not round

 

I can answer that! COST if the car companys made the frames out of tubing it would cost a fortune. your gonna pay some wheres around $200 for a set of two tubes now think howmuch it would cost for a whole car made withit. I kinda like the TDS ones and as soon as i have money will be geting some.

 

I raced several years on the Global West units and am happy with them. Besides, you can jack the car up on them.

 

The ones TDS sells are Alstons. They tie in to a different part they don't run down the pinch weld like others. the actually connect the front subframe to the rear subframe right in front of the rear control arms. You can add those to ,i'm pretty sure, about all other brands of sfc's.

 

I have a set of Hotchkis SFC's and I must say it was probably the best upgrade suspension wise. Along with a 3 point strut tower brace, 34mm sway bar, ans a Spohn 1 1/8" wonder bar; car handles awesome.

 

yes i am aware of how they route them thats why i like them better than the others. the TDS ones will conect the subframes and make esentially one full frame rather than two with a funky angle thing. i can see the benifits of the others for a lowered car but i dont plan on droping the car as i take turns at 60mph and dont have any control problems. heck my car sits so high i can drive up and over a curb or parking lot bump stop and not scrape a thing.

 

Just because its round doesnt mean its stronger. Material, size, thickness all enter into it. Unless you sit down and figure out the properties of both set of SFC's, any claims one way or the other are only personal opinion.

 

I have the old South side machine square on mine and i love them

my friend has the round 1s and he loves them

Ive driven his and honestly not much difference at all....

point is they both work

 

Yes, Very true.

Lets compare then.

UMI- 2.0" x 1.25" ERW rectangular tubing [45,000 psi tensile strength steel material].120" thick mild steel/ 2.45 lbs per ft

SPOHN- 1.75" DOM seamless round tubing [80,000 psi tensile stength material] .120" thick mild steel / 2.08 lbs per ft

 

Nice user ID, very appropriate

UMI's look similar to the SSM's and the factory vert 'sfc'. There is some benefit to being able to weld to the rocker but who knows how much. I do have a couple cracks on the rockers where the SSM's are welded on my car so there is some force being transferred there.

 

you know i couldnt deside between the alston sub frame conectors or the ones from spohn so i ended up getting both now u wanna talk about no flex yea... so i guess my point is its all a matter of oppinon on what you think is best for you and how much u wanna shell out for subframe conectors

 

how did you have to modify where both sets attach to the LCA bracket?

 

Yeah I had a chance to drive mine before they were welded. It made a big difference to have them stiched along the pinch weld. Subframes really show you where the weakness is in the suspension thats for sure.


Oh btw..Dean... your really into the handling part of these cars. So.. you know what your talking about. IM just happy with my install. Round or not.....

 

Well if my calcs are right (didnt go to far into checking, but numbers look right)
The round bars vs square, end connected only:
77% stronger in torsion
63% stronger axially
Pretty much identical in bending, on the strong side of the box. I dont know how they mount in the car, mine are mounted what I would consider weak side, based on the loading its likely seeing in real life.
Err... I did not write down shear. The boxed would fare better, as a guess since there is more area of steel in cross section.

The round would be weaker or close to same if the yield strengths were identical. There would be no disparity.

A rough sqaure/box framed up system with vertical deflection at a single corner shows the tubing doing better, again all due to the yield strength difference.

The square bars, brackets/flanges aside, are only about 4# heavier based on 5.5' long connectors (about what I measured along the rocker) and the weights listed above. Not all that much, but if you are watching your weight I guess you need to go on a diet if you choose the square stuff.

Anyway, in car what the SFC's are trying to do is minimize deflection. Neither should come anywhere near a failure point, so talking about ultimate strengths is pretty moot, more important are deflections. Also torsion is going to be the least of your worries, if you take a look at how and where they connect and what the frame is doing, the twist is very minimal compared to the bending and shear, and that showed up on my model. If you were really concerned about torsion, the square tubing is better if it can be seam or stitch welded to the rocker. If you look at the equation for angular deflection based on torsional forces, the length of the element in question factors in. If you can stitch weld the square and not the round every 6" or thereabouts, the rocker adds to the strength of resistance to some extent since you'd likely only be able to weld one corner of the square tubing. This will also effect bending and shear strengths, with the added connection points along the member, less free unconnected/unsupported length. How much, arguable. I dont plan on figuring it out. I'd say there's some benefit to the square vs round if one can be stitch welded and the other not, for obvious reasons, but the round tubing has some additional strength of its own to compensate. Its still a pretty long free span, however. So I'm not sticking my neck out and saying one is better than the other but you can decide on your own. Both likely do a significant job of strengthening up the chassis as its a wet pretzel to begin with. Are the sqaure ones stronger by themselves end connected only, like they claim? I'm gonna say... no, sorry guys. Maybe if you used higher strength material. The DOM and ERW arent gonna matter though, as I said in a situation where deflection is the concern the last thing you should be worried about is getting near the yield point, you shouldnt be near that point. Closer you get, you are talking about large deflections and you really need to use a bigger piece of steel.

 

UMI's subframe connectors used in conjunction with a Spohn tubular transmission crossmember gives a very solid ride. I like how the UMI's and Spohn subframe connectors add a link to the transmission crossmember area.

I wish Kenny Brown made a "Diamond-style" connector for third gens. It is by far the best produced set-up, IMHO. They can be had for 4th gens.

 

I'll jump into the foray, I purchased these bolt-ins from CGS Chassis for $160. My engine isn't built up too much so I wasn't worried about the "bolt in" type. Plus they can be welded when I'm ready. After the installation I did notice a harder ride. I was wondering if placing a polyurathane bushing or "biscuit" above or below the washers would take some of that harshness out of the ride and then weld the front and back bracing. Or do you need to seem weld the entire length of the subframe?

 

A bunch of great posts here, huh?

Lets start with the obvious, tensile strength has nothing to do with how the tube is formed, it depends on the material used. Most subframe connectors are made of 1018 or 1020 steel, which has a tensile strength of about 70Ksi no matter if it’s ERW or DOM.

If you want a stronger material, go with GW, which is I believe the only company that makes chrome molly (4130) SFC’s for our cars. Of course, real world that is a stupid reason to make that choice because normalized 4130 has almost the same tensile strength (about 75Ksi) unless it’s heat treated, and 4130 doesn’t like to heat treat to any significant depth, like .120 is difficult. Real world, unless you find some way to heat the SFC’s to over 1200*F and keep them there for hours AFTER they were welded onto the car you really don’t end up with anything stronger, but you do end up with something with brittle points around the welds.

The fact that the box stock is ERW has almost no effect because of it’s shape, it’s unlikely to split a seam before it deflects. For the most part the same is true of ERW round tube but it is actually more likely to split a seam and fail that way.

Now yes, mass for mass round tube has a higher torsional stiffness then box section, but in this application you’re not twisting, you’re bending. If the SFC were run up the middle of the car where the DS is then it would be twisted along that axis, but instead most of the connectors that we’re talking about run along the rockers where the forces exherted on them are bending forces. Welding them along the rockers not only increases attachement points but further makes sure that they CANNOT twist, making rount stock’s torsional advantage even less of a factor then it already is.

Now someone go and calculate resistance to straight bending forces when both types of tubing are supported so they CANNOT twist and tell me which is stronger (hint, box stock in the same size, but that’s irrelevant since the box section SFC’s are actually LARGER anyway).

The jacking point argument… I’m not sure that I can make coments about it without calling someone names, I’ll stay clear of that for now.

If you want to do this right and really stiffen things, then you should make them out of 1025 box stock and section the floor pan right by the rockers and tuck the stock in there and weld it the whole length, and then tie a proper cage into the top of it which also ties into the A and B pillars as well as the roof and you’ll have something that feels like it’s carved out of a solid block of steel.

 

http://www.swracecars.com/camaro_boltOn.asp
Check these guys out, they advertise in GM High Tech Performance. In the picture, they look like they'dd be stiff. But I think they are bolt-in. I'll have to look again to see if weld-in.

 

SPOHN..

 

For the love of g()d, The boxed SFC's ARE twisting.

The chassis exerts twisting force on them. They are not bending up and down, they are twisting and allowing one side of the car to go upward and the other side of the car to go downward while the outer SFC's are remaining flat.

They are twisting torsionally. This is why round tube is so much better for torsion. Heck, I don't ever recall any time in history when someone has used square tube for torsion or swaybars.

Try this people. mount a square 1x1 tube vertical with a cheater bar welded to it and try to torsionally twist it- low and behold, it twists easily. Now try the same with round tube of the same size, it is very hard to torsionally twist it- hence why it is used for heavy torsional loads on car suspensions (aka. torsion bars and swaybars)

Geez- its like pulling teeth around here trying to get factual info into peoples heads where they can grasp it.

 

So why do you keep coming back Dean? How many times must I tell you, you're perfect 3rdgen.org material. Get your *** over there.

 

I'll check it out Cheyenne. It just kills me to see other people posting nonsense and flase data- I am unable to non re-register and correct this travisty Besides, Its fun just to see how long it takes for someone to finally reconize me with each screen name I pick- I figured this and the last would be oh so obvious.

But for the mean time, maybe just maybe one more diagram might just help people understand that they DO TWIST.

Please study carefully. Boxed SFC's will twist and cause the chassis to flex in cross wedge like how the chassis does without SFC's and still allows more potential for suspension geometry change during cornering loads.

 

Checked it out brefly but enough, from the juvenuile comments from the members on this link, I will have to say I graciously decline. thank you though. http://www.frappr.com/3go

 

round is light, square is heavier,round has decreased bending strength, round can be had in stronger material to counter act this decreased bending strength.

Perimeter style subframe connectors aren't subjected to much torsional load if any as they go on the outside of the car. These are subjected to front to rear loads. All the torsion is on the crossmember. The ones Alston make are subjected to alot more torsional stress as they are in the center of the car.

Personally I have the alstons and the UMI's price was a big factor, that and welding round to square on the outside wouldn't have been much fun, whereas the square to square worked out rather well.

 

The torsion is on the crossmenber? Only pertaining to motor torque on launch- Otherwise- No, the torsion is on the wheels ands suspension acting upon the chassis trying to push and bend it . I give you all these diagrams explaining to you how and why- and you still come into here and post there is no torsional load on perimeter SFC's. PLEASE GIVE US A GRAPH OR SOME INFO BACKING WHY YOU MAKE THIS STATEMENT. I have giving plenty of factual graphs explaining the exact opposite of what you just said- so give us something to back what you preach. I'm waiting patiently.

What you are saying about twisting of the chassis with inner SFC's as opposed to outer SFC's IS CORRECT, but that is not the part I am trying to explain here. I am talking how the SFC's will still twist easier on the perimeters if they are boxed SFC's as opposed to round SFC's.

 

Well Mr. expert, how about rather than drawing silly diagrams and making grand claims, you actually post up some numbers regarding the torsional stress and bending stress of... oh lets say the round tubing, the square would be too difficult for you, with a 2" vertical deflection on one corner of your box, other ends fixed. Hell I'll even let you double it up with moving the opposite corner. Dont try to weasel out of this either, you brought it on yourself. Post up the numbers or shut up.

And dont misquote me either.

BTW I hope you dont get kicked off again before you can respond, seriously. I want to see this for myself.

 

Hey college fatboy, Looking to get your *** kicked again talking to me that way?

How about I take the ol school prybar I can twist that squared tube with and shove it up your *** college boy. Doesn't take a bookworm to actually grap someting and twist it. Try it some time.

1" sq tube Vs 1" round tube/ both .063 wall- Don't hurt yourself.

 

See, thought so. You cant. Only thing you can do is attempt to threaten and insult. Oooh I am so scared. Not. You also have your 'facts' wrong, guess you are still living in the past.

Want me to school you on structural? I can. Thats the problem, you dont want to learn. While you can teach, you could learn too. I was actually trying to be helpful but figured you'd get mad when someone disagreed. What a shocker there.

So anyway, subject at hand...
Take that 5' long connector, move it up 2". Move it over 2", doesnt matter. It moves in an arc, as you know. Whats the resultant length? 4.997'. If that .003' were to cause a twist, it would amount to all of... 0.95 degrees. Lets see... 2", 0.95 degrees... pretty obvious.

Built one of these before? Designed, built, and tested. Works too. I might even tell you what it is. Might even support your car, it'll hold at least 2000#.

 

Man I'm gonna get deleted, I just know it.

I should put a thirdgen model in there... photoshop.

 

Dear engineering boy. Fact has it that any reputable chassis builder will tell you these proven points from years of trial and error- I thought this was common knowledge, but I guess not.

Here's some basic covered facts from a reputable race chassis builder on tube torsion and few other facts.

Remember- I posted the comparison between Spohn round tubes and Umi sq tubes. One was DOM steel, the other is ERW. Both basically the same weight tubing (i.e.-the same size).

You just don't get it do you. The *attack * has nothing to do with this post- Its the fact that your father has said some things to me on a personal; bassis behind his computer wishing harm upon me by someone else- Fact is- You are both two faced peices of sh*t and I will smack the both of you around (together)next time we cross paths for trying it instigate harm upon me. teach you to keep you fat fuc*ing mouth shut and mind your own business.-It is now personal fatboy.
---------------------------

Round Tube vs. Square Tube Analysis:
There is ongoing discussion and debate about the use of round vs. square tubing in frame design. Most of it is from people who are selling one or the other. The bottom line is that it costs more to produce an original style round tube frame because it's more difficult to design and manufacture. Many companies have taken the easier path of making square tube ladder style frames. FFR felt that their challenge was to make an original style frame stronger without losing the beauty or period correctness. Good engineering means form and function. Once they decided to go to the trouble of building a round tube frame they found some pleasant surprises.

* Round tube weighs less than square tube.
* Round tube is available in stronger steel. There is no rectangular 1020 DOM tubing, it is all 1010. 1020 DOM is about 30% stronger than 1010.
* In torsion, (exactly the kind of stress that cross members are subject to) round tubing is much stronger than square tubing. Makes sense why there are no square driveshafts, right?
* Under vertical bending loads, square tubing made from the same steel as round is stronger, but since the round tubing is available in higher-grade steel, there isn't much difference between cold rolled 1020 round tube and square 1010 tubing with respect to vertical bending loads.
* The end result of using round tubing is a lightweight ladder frame, with superior torsional load rigidity and vertical load resistance equal to most any square tube design. It's one tough frame!
* Square tube frames are more common because they are simple, easy to design and the materials cost less. They can be made strong, but sacrifice beauty. A well-designed round tube frame is the hallmark of professional chassis engineering. They are complex, requiring intricate jigs, difficult to design and they are usually made from better materials. They are also more beautiful.

One final note:

All of these frames work. It's probably more a question of aesthetics, materials and cost. The next time someone tries to sell you on how much better a square tube frame is over a round tube design; keep a few things in mind. The 1020 DOM 4" round tube that FFR uses for its main rails and cross members costs $8.75 per foot. Square stock tubing (commonly used) costs $1.98 per foot. I doubt the folks selling you on the virtues of their square tube frame told you that. Race engineers use the more expensive materials because they are better.

 

The stuff in bold i agree with. Round is much better handling torsion vs. square it's a fact

but...

since the load is vertical on the sfc's I don't see it having much torsion at all granted the k-member ,crossmember, and upper panhard bar on our cars. with your design your putting forces on a single center point between the two braces. As i said with the design of our cars the deflection would be so small that the torsion amount put on the car would be minimal. So in reality it's only weight savings unless your car has 700ftlb of torque or more in which case you'll probably need a full cage to drive it anyway. Alot of the local guys run 4th gens and they have basically the same suspension except for the coil overs.

I would have went with tubular sfc's if i wouldnt have gotten a discount through UMI. And with Steve Spohn's pricing he's pretty hard to beat regardless, and he carries a hell of a reputation among the 3rd and 4th genners. And with him saying he "overengineers" everything I'll trust him especially since i think in 2002 he changed from boxed to tubular sfc's and people haven't had any complaints.


And in reply I've talked to the guys at factory five racing on a few occasions even visited the shop while on a road trip. That's where you got that information from. Even so they use both tubular and square tubing in the designs of their cars.

It's pretty much a meek point to argue with anything as until someone can verify and get actual readings no one is going to believe one is stronger than the other. They've made up their mind. We need someone with hard data!

 

Wow, having to quote someone else. Trying hard?

And I really dont care what your beef is with my dad, it doesnt concern me. Keep it to you and him. Dont start personal **** with me. I will not take lightly to it.

 

IM, your 'analysis' of the chassis ignores something important, what the subframe connectors in place are experiencing. I tried to tell you, you arent listening. If it was in the middle of the frame, sure... it'd be in torsion. Its not, its on the edge of the frame. Its not seeing any significant torsion, same thing I said before. You really need to do the evil deed and stick your nose in a book and learn a few basic things because quite honestly its a pretty basic principle. Armed with that information... well with what you are doing to cars, it would be quite helpful.

I already know about round v square. We werent allowed to use round for our project, its against the rules, well unless it was solid. No hollow round tubing. We all would have been using it otherwise, no secrets there.

FYI in that pic:
I used 4130 seamless mil spec 90ksi .049 and .035 wall square tubing, in 3/4" and 1/2" size, respectively, to build a 3' wide, 3' tall, 14' long clear span bridge, built in 3'max long, 6" high tig welded trussed sections, tension rod crossbraced, with 4' long cantilevered ends to hold 2000# center loaded with less than 2" deflection, less than 2" sidesway, and 1000# center and canitlevered load the same criteria. Square tubing. 95# total bridge weight. It was also designed at the edge of breaking, when you have things like a competition where weight and deflections are a huge factor, you want to throw any overdesign and factors of safety out the window to save weight and design appropriately to minimize deflections. This was actually not my #1 choice, the head of the team picked it. The winning bridge was almost a carbon copy of my #1 design. We built one section and broke it to test the failure point vs the computer model I made, funny they matched. Trust me, you can call me college boy all you want, I know what I'm talking about. If I worked for a structural engineer for a few years, I could take the test to be licensed in structural engineering.

Check this out:

http://www.hendrickmotorsports.com/t...360.asp?bhcp=1

I think I see square. No doubt them Hendrick boys are slow.

 

Talk IM into putting strain gages on his car and taking it to the track. You wont get better data than that.

 

This is where I am trying to explain to you where you are mistaken.
Fact is, SFC's are NOT a ladder type constrution. What does this mean? It means that there is no ladder bar type cross members along the two SFC rails connecting one side to the other. SO..The one side is not locked into the other side with in sync vertical movement. Ladder cstyle crossbars along the 5 ft span help eliminate rectangular tube twist along its 5 ft lengths and ties both left and right rail together in sync.

Since they are not ties together in sync, the left front SFC rail can go up (keep in mind the entire SFC rail on that side is not bending up- however the span of its length is twisting) allowing the other side of the car to stay level since the twist of the sqare tube in torsion from rear to front allows the floorpan to tweak still. Round tube does not twist as easily in rear to front torsion along the rails SO... the left and right sides of the car stay better in sync WITHOUT a ladderbar style contruction.


And to the fatboy- your scale model you show is trangular I-beam rails mounted on solid pillars so there is no road tension or suspension acting upon your model- it is a far strecth to compare that structure to a loads a frame will encounter. Try taking your pillars off and mounting a suspension and wheels on it and watch that baby flex on those side crossbars frnt and rear while the rails do not bend verticaslly, but infact will twist without the solid floor mounted pillar risers and wire supports.