I read a bunch of threads on this topic and I'm still unsure if I will feel shortchanged if I only did the Spohn outer weld in subframe connectors.

I have an 88 GTA, 5.7, hard top, TES headers, 3" CAT Back. No mods to engine and I do not race - just a weekend driver.

I was thinking to do these AND inner SFC's as well but is that overkill? Do you really see a difference from adding the inners? My main concern is ride quality - the roads are TERRIBLE in my town so I'd like to cut down on the squeaks, rattles and flex on the car. I'll do both IF it makes a difference. And in that case...What should go with the Spohns?

I spoke with Spohn about this, by the way, and they said inners are not necessary in addition to theirs and that I wouldn't see a difference.

 

I have UMI outer SFCs and MAC inner SFCs. First I installed the UMI then a year later the inners, they both made vast improvements and together left the car feeling brand new, they removed all the squeaks and rattles. If I had to pick one I would go with the outer style, but if possible do both. With factory spring rates a single set should be fine but if you're running higher spring rates you may benefit more from the added bracing to keep the chassis from flexing and making the spring and sway bars do the work

 

http://www.swracecars.com/store/82-9...70=40-600.aspx

These tie the rockers/subframe/floorpan into one unit. I have it on my car and I couldn;t be happier. Only caution is if you are planning to lower your car the rear control arm mounting point might occasionally scrape if you hit a bump too fast

 

I've thought about taking the S&W racecars setup and welding it in... haven't done it yet though...

 

On a typical street car, driver, cruiser, IMHO inner and outers are overkill,

Heck, I've had people on here argue that any sfc is overkill, but I disagree.

There are plenty of real fast 3rd gens with only one set of sfcs.

I think it comes down to a weight vs strength question.

Do you really need the extra strength vs the extra weight?

 

I welded in my umi outer sfc's and it made a world of difference. No more noticible flex. Now when i open the doors the car doesnt sag (ttops). Its a street car, no rattles on bumps. Defiently recommended.

 

Thanks guys.

I guess nobody on these boards has ever said "I installed the outer SFC's first, tested them, then installed the inner SFC's and there was no additional improvement".

So if it's true that adding the inners in addition to the outers WILL indeed noticeably improve things for me, even just tooling around town, then I will always feel regret that I only went with the outers and it will drive me nuts until I get the inners.

 

You'll be more than happy with just the outers.

 

OK, just ordered the Spohn's from Hawks. Will have them welded in and see how I like that.

Next up I will do the Edlebrock strut tower brace and the steering Wunderbar.

Thanks for the help guys.

 

I bolted and welded mine and couldn't be happier.

On a streetcar,driver,cruiser weight is more than likely not a big part of the equation either, at least not the small amount were talking about here.

There is nothing more annoying than seeing those little cracks start to appear in the corners of the roof after you spent hundreds of hours making the paint perfect. So given the the choice, personally I would choose strength and sacrifice a little weight. That's why in my opinion S&W is a nice option that addresses both issues at the same time

 

My car has 170k miles on it...and I have a little crack like that driver side roof...My car is LONG overdue for the SFC's! Crazy thing is my car was owned by a mechanic before me and he didn't fix anything as it broke; power door locks, cruise control, VATS, hatch motor, hatch shocks, exhaust, spoiler....He just kept it running as it all fell apart around him.

 

I understand thats quite common that mechanics don't keep up their own cars as well as they could. Its understandable, if i worked on cars all day i doubt i'd wanna work on mine when i got home too. One of the reasons i didn't become a mechanic.

Anyway, back to the point. I bought UMI outers, haven't installed them yet but i will as soon as it warms up and the rain washes away the salt. TDS wonderbar too! The only good thing about storing the car for 5 months a year, STOCK PILING NEW PARTS!!

 

What color are your UMI sub frame connectors ? I'm also going to use the UMI sub frame connectors so please take photos of the install so I can get a look.
I also went with a UMI Wonder bar = https://www.thirdgen.org/forums/afte...r-bar-1-a.html

 

Actually I did, 1st umis on a hardtop and then added alstons. Nticable difference!

 

I'm going to start with the Spohn weld ins, the Edlebrock 3 point strut mount, and the Spohn steering brace. Those 3 things should fix me up pretty good for a while.

 

I'd suggest after market strut mounts before or in conjunction with the STB. Modification of the mounts may be required.

JamesC

 

UMI SFC's it is !

 

Lets give some hard facts-

Round tube is stronger than square tube when the same mass is used.

Torsion resistence is better with the same round tube (twist force as in jar & lid)

To give an example of equivilence in strength of round tube and square tube.

If you take 3/4" x.065 square tube, it is the same weight (mass) as 1" x .058 round tube.

3/4"x .065 square tube will hold 1066 lbs
3/4"x .065 round tube will hold 625 lbs (but alot lighter in mass than 3/4" sq tube)
sooo...
1"x .058 round tube (same mass as 3/4" sq tube, actually still just a little lighter) will hold 1445 lbs

Umi SFC's are 1.25" x 2" rectangular tube- (average torsion is 1 5/8") x.120 wall

Spohn SFC's are 1.75" x .120 wall round tube.

Spohns have alot stronger torsion resistence. Also when you increment weld them along the span, it greater strengthens both units tied together from flexing upon eachother- they work more as one thicker unit rather than two thinner units. Their load span shortens which in tern makes for stronger support when tied together with the rocker panel.

I choose round tube over square tube for this very reason.when talking in torsional twist of chassis forces like I described in another post about the front and rear lateral vertical walls of the 3rd gen chassis. The SFC's are not just lifting in beam load, they are keeping the independant sides in uniform of lift with torsional load. The 1.25" torsional load of the UMI does not compare to the 1.75" torsional load of the Spohn design.

Plus I like the round tube for a jacking point- it gives the jack cup a nice rotation surface as the car lifts and keeps the cup centered under the tube at all times for safety. (I jack my cars frequenly so this is important to me). The sqaure tube frame on my truck scared the heck out of me so I am very cautios jacking that. I have reinforced the frame rails inside it with round tubing layed inside the C channel framing to strengthen it years ago because it torsionally flexed terribly. I carry alot of weightin this truck and the squared c channel frame was not cutting it in torsional deflection. You could littlerally see it by the naked eye- not anymore.

 

Good info, but you did not answer the OP's question.

For a street car, do you need 2 sets of SFC's?

 

I also want to add that square tube is used often in Airplane truss structure ONLY in traigulated truss form because trust struture when engineered properly does not have any torsion bend load- It only has compression and tension. It is easier to fabricate and weld square tube especially in truss triangulation form (think of a lifting crane structure- boxes of metal with triangular supports in each box struture).

We do traingulation in the subframe, but it is triangulation of the longitudinal beam of the outer SFC style with the firewall shear wall unibody struture to keep both sides of the chassis uniform.

Spohn is so far still the best out there for ultimate handling and chssis rigidity when installed properly.(My opinion)

 

no, Not for a race car either if you use the Spohn SFC's and install them like I did with increment welds on the beams like suggested in Spohn's installation instructions

My car would teeter totter the RF and LR wheels intermittently off the ground when the RR tire was backed up on a standard residential curb aporx 8" tall. I have posted pics of this many times on TGO. I am the only person to ever show this that I know of. This is done as a real world test with the proper load of the tire footprints transmitting torsional deflection into the chassis through the spring pockets of the chassis. I could not do this prior to the Spohn SFC install. I have tried it wil a few friends cars (one with Alstons (Mitch), and one with Global West (Sterling) and they would not do it on the same curb. Even worse was another friends C4 vette(Dean also)- could not believe the frame flex on that thing. his doors were binding.

I certainly do my research, and them I also test things afterwards. If I have a product I am not happy with, I have readily posted that info to others as a buyer beware. I do not jus tlist products are great becasue its what I have. Case in point were my Hunter Aluminum strut mounts. They were the original prototye design before anyone started making any aftemarketr units. I was one of the original test guinea pigs. To date I am the only only I know of that had failure with the aprox 20 sets that were produced because I exert alot more "testing force" shall we say to my parts and the aluminum started to stretch in no time causing slop in the bearing reatainer section of the strutmount. Steve Spohn consulted with me years ago when he duplicated the prototye and stated doing production runs of it in mild steel.m It was a great design from Hunter, just poor choice of material.

 

Good to hear, and as you may notice, I am in full agreement, that inners and outers are not needed, and just adds weight to the car, and takes it out of your wallet.

Buy the spohns, and take to other $200 and spend it on something else!

 

Thanks SlickTrackGod. I am bringing the car to a body/frame guy that has been doing it for 60 years so I trust him to check my frame, then weld on the Spohn's exactly as the instructions tell him to.

I guess the answer to my question may be that while my car will not NEED additional SFC's to the correctly installed Spohn's - I MAY still benefit from it. I will probably spend the money elsewhere.

 

You DO NOT need inners.

I seriously doubt you would notice any difference if you installed them later after you installed the Spohns. Just adding a lot of weight with a little gain that again you would never realize, especiall on a street car.

Agree, put the extra cash towards some good struts.

 

I did alot of creative bracing on my old car.. I did alot of creative modifications to it also- withthat said, it was very low to the ground and I did not even have the consideration to even put inner styles on my car. Would they have helped? Depends how you look at it. Of course anything with more support will help with bending, but help in weight> yes AND no. Depends on how and why you need to add that weight- A whole nother diuscussion which I have gone over in other threads. if you want more? I would personally contact Steve Spohn and see if he'd make you a set in .188wall or even .250 wall. I would rather have that then add outers AND inners. Just more of a good thing rather than a good thing and an OK thing.

 

Actually I would put all of my money here first until I bought some at least high end dampers. I am consulting and helping a friend right now as we speak on his car. He can not afford much and is a major NASCAR fan with a badass looking DaleJr replica 3rd gen. I am helping him do a Boomtube exhaust in a few weeks (we were just measuring for tubing bends etc two days ago). He is more into looks and barel drives the car but probably 500 miles a year. The car has about 400hp but the suspension is less than desireable so I am also trying to help him with a budget build so he can at least get the thing places a little better without tearing up his floorboard (and current exhaust :duh: . Since he can not afford Koni Yellows at $280 each. I told him to at least just get a step up for OEM with some KYB gas charged struts to keep him from bottoming out. No need to go mid range since I still say they are not worth it for performance.

The aboslute best thing you can do to these cars after tires and shocks is to replace the OEM strut mounts with some aftermarket solid strut mounts....period... if this is a daily strret car of if its a track car regardless. This makes the car controls more percise and responsive- its a safety thing like brakes etcs. Then I suggest going SFC's as you get into pushing the car hardered and twisting the chassis. Doesn;t matter what you do to a car modification wise if you do not have traction, brakes and steering. A stiffer chassis will not matter if those other thangs are not better first. Shocks and tires are grip, brakes are brakes, and strut mounts are steering reponse control in case you need to swerve etc. Those things make a car safe to drive faster fwy speeds in preperation for a panic situation (accident in front of you, etc)

 

For a same diameter and wall thickness a square tube will be stiffer than round, however the round will have a significantly less cross sectional area (and weight), if you even out the cross section (larger diameter round tube) the difference will be less.

If weight is no issue and size isn't either, a square and round section, same weight, same wall thickness...the round will be stiffer.


D = OD, d = ID
____________
Area of round tube = PI/4 (D^2 - d^2)
Area of square tube = (D^2 -d^2)
Moment of inertia, round tube = (PI/64)*(D^4 - d^4)
Moment of inertia, square tube = (1/12)*(D^4 - d^4)

Torsional calculations assume that the torsional moment will be applied at the axial center of the shape. The problem with evaluating frame cross-sections is that the applied torsional moment may not follow the centroid of the structure and may also be combined with bending or other forces.

 

Thank you for confirming all that. I stole those calcualtions from something else and have a hard time myself with formula's. I am back in school as we speak at the age of 46 going for a "formal education" to support my streetsmarts. It is hard for me to explain things like the cross section of the corners on sq tubing. I understand how it fails in torsional twist, but I do not have the education to explain it to others. I have learned things through trial and error as well as alot of down right overengineering just to be safe. The trial and error has been a gokart sand rail I built a decade ago and would purposely try to break it- I usually did, and thus learned alot of learns on fabricating and structure.

 

My opinion is that while they may add weight (about 40lbs or so?), it is atleast at the lowest and most center point of the car in between the wheelbase, which lowers the center of gravity actually. They do cost 150-200$ and they reduce ground clearance slightly (although for the record my 3" flowmaster exhaust hangs down just as low as my MAC inner SFC's, and it's not usually the middle of the car that scraped, it's usually the front or airdam anyway).

I put these on first in 2007 and added SPOHN's 2 years after because I wanted more chassis strengthening (I have ttop car.. enough is never enough). The MACS made a huge noticeable improvement, and the SPOHN's added rigidity as well but it was most noticeable when I would put my car on a lift and would notice the doors would open and close now MUCH smoother and without rubbing from the body flexing. This was probably due to the fact that they are stitch welded along the rocker.

I think having both is not necessary, just like poly/rod ended bushings are not necessary either, when rubber works perfectly for most people on the street. But for those who look for the most out of their cars performance-wise and want to add rigidity to their chassis, even if the SPOHN's are better vs any inner in comparison, the fact is that adding the inners to the outers does increase chassis rigidity.

ps. and by no means am I saying adding the inner SFC's will have the same effect on the car as adding poly or rod ended bushings, just used it as a loose example here

 

Again, on a track car sure, but the op just wants a good solid driver.

 

My car is not a track car by any standard. It is driven 99% of the time on the street, hard, and over bumpy and uneven roads, and dips and rises, etc. Having a solid chassis for me was a priority even for street driving. For me, it did make a difference even on the street, although I cannot say that adding the inners AFTER the outers will have the same effect (I did it the opposite way).

 

From OP, Of course, this is a moot point now. He has ordered the outers, and talked to spohn as well, who told him he would not see any benefit from the inners.

 

the actual necessity of dual sfc's seems to be subjective here.. I suppose for the average person outers or inners for that matter would be enough. For what it's worth, I was happy with just the inners, but wanted it stiffer (why does this sound funny.. lol)

 

I agree, and thats the point I've been trying to make.

For the typical guy that just enjoys cruising around on the weekends, any sfc would be of benefit.

For the more hardcore guys, they May be some benefit to both.

It would be awfully hard to really quantify this though.

What would the tool to measure be? Lap times? too many variables.

And as I stated before, most of the fastest 3rd gens out there only have one set of SFC's on them.

Of course, if you are beating on your car that hard, you porbably are required to run a roll cage per sactioning bodies, then IMO, the second set of sfcs are really doing very little.

 

I feel like I have my answer and am 100% confident with my Spohn purchase. Thanks everyone.

 

Point well made unless your car is a donor like mine. I have an 89 IROC 1LE that was horribly abused by the person who owned it prior to my brother's purchase. My brother left it to me in his will and now I'm the proud owner of a veeeeerrrry expensive project!!! I don't know how bad this car was abused, but the original motor was gone along with the original TPI, and the original rear disc brake axle was gone as well. I ran all the numbers, VIN, transmission tag, frame and body tags with my local Camaro expert so I'm certain of what I own. He wants me to restore it. But with a destroyed engine, trans, brakes, body work, and interior, I don't have an extra $120 grand lying around. Anyway, I am building the car for Pro-Touring I've already built the motor dyno'd at 580 hp and I intend to add an additional 400 of NOS. Why is this important? This car will be driven on the street, autocross and the drag strip. It has to be very stiff. i.e., no frame flex. So, my question is, will the S&W be enough with a 10 point cage?