pgh1992

Getting ready to drop in a new motor and rear end in my '92. Just wanted to know how much power the frame could handle because the car has t-tops. Not sure if i need to run subframe connectors or anything like that.

//<86TA>\\

iTrader: (14)

subframe connectors are a must, even for stock 3rd gens, have them welded in.

1MeanZ

iTrader: (9)

some people on here will tell you they are a must but I think thats a bit excessive. It depends on what you do with the car and how much power it will actually have. Yes these cars do flex, but I've never heard of one breaking or being damaged permanently. By comparison, 2nd gen T-top cars will actually break the T bar when punished.

If you autocross or road race, SFCs are certainly of use even at stock power levels.

If you have stock or mild power levels and it's just a street car I'm not sure they are of much benefit.

If it's a drag car, frankly I'm not sure where to draw the line there. There are a couple guys on here, one white IROC I know of that runs 10s and he doesn't have SFCs and claims to not need them.

8t2 z-chev

getting the chassis rigid is one of the best modifications
that can be done to a third gen-GM slipped up bad when
they designed the chassis of the third-subframe
connectors are a good start,welding certain body seams
helps too.Also the front structure ahead of the firewall
is not overly rigid,causing what i'll call"doghouse shake"
strut tower bracing and an extra x-member just under
the fan area will eliminate that.
a rigid third drives oh so nice

1BADRZ28

iTrader: (2)

Why would sfc's be excessive? They are an easy install and do not get in the way with anything on the car. IMO one of the best upgrades even for an all original car.

JamesC

iTrader: (5)

Check behind the drip rail of a thirdgen, even the babied ones, and you're likely to see stress cracks. +1 for SFC's.

JamesC

mister_hudson

iTrader: (3)

Better to be safe than sorry! They are a little extra weight but the benefits far outweigh...

1MeanZ

iTrader: (9)

Far outweight what? What exactly is breaking on these cars with lots of power?

Excessive would mean money spent that you don't get any benefit out of, and weight you added to the car that gains you nothing.

James, I 100% know what you are talking about and recently I found out what REALLY causes the sail panel tear you speak of. For the record, my passenger side sail panel is severely torn on my IROC. I discovered the real cause of this when BIGMODS and I cut his T-top roof off his Camaro, and swapped on a hard top. The tearing issue is just as common on hard tops as it is on t-top cars from what I've seen.

The issue is caused by a bad resistance weld right at the corner where the window seats to the roof. There is a fairly thick metal strap that is welded vertically from the side of the sail panel up onto to the flat part of the roof of the car. It is common for one of these welds to break off the roof skin leaving it unsupported in the corner where it sees the most stress. The tear is caused and made worse by opening and closing the door, especially if the window is adjusted up too high on a T-top car.

My tear has gotten worse over the years and I've had sub frame connectors on my car for a long time. You can see it open and move when you close the door with the window up. Again, this issue is caused by a broken spot weld on a support stamping inside the roof and is exacerbated by opening and closing the door, and window adjustment.

Again, I'm not saying SFCs are bad. I'm saying for a mildly driven mildly powered car, I'm not convinced they are worth it. I think the cars that need SFCS worst are cars that are autocrossed or road raced, especailly on bumpy courses. For lots of power on slicks, I think they are probably a good idea for drag cars too.

A few more grains of salt
https://www.thirdgen.org/forums/orga...-touching.html

https://www.thirdgen.org/forums/orga...hsr-first.html

(this is the white IROC I was talking about not having SFC)
https://www.thirdgen.org/forums/orga...y-but-new.html

JamesC

iTrader: (5)

And exacerbated by unibody flex, I assume, even if the cause is elsewhere (Could we believe that the weld itself is broken by flex?).

My stress cracks haven't shown signs of 'growing' and/or moving since I installed SFC's. Interesting comments. Thanks for the input.

JamesC

1BADRZ28

iTrader: (2)

I'll take my sfc's anytime. I call rigity part of the equation. Any car feels more solid with them. I wonder why they were even invented if no one needs them.

radical82

Stiffening the chassis is the best way to let the suspension do it's job without flexing the chassis.... Hard to account for flex when setting the chassis for good handling or even a bracket car... Without a good firm, non-flexxing structure, how can the suspension components perform correctly??? But if all you're doing is cruisin' on Saturday nights, doubt you would notice the improvement a rigid chassis brings... If you're going to be doing any performance or race driving, then IMO it becomes essential to first have a non twisting structure....

1MeanZ

iTrader: (9)

The weld could be broken by chassis flex or by the door closing. I have no data either way and I am certainly not disagreeing with you. I just want to challenge the status quo here a little to make sure we're all thinking for ourselves and not spending money blindly just because some guys on the internet says so.

FireInMe17

I wish I had money to get some, sometimes I wish the car was a bit more rigid, and sometimes the front end will shake a bit but it seems to come and go. SFC's would fix that.

8t2 z-chev

even if nothing ends up cracked or distorted from flex in
a stock,non-SFCed third they just drive and cruise so
much nicer when the flex is eliminated-most rattles and
squeaks dissapear,handling is improved,can't feel the
steering wheel moving from side to side in your hands,
can jack under the SFCs,etc etc.
Back in 1990,a buddy showed me his brand new '90 FB
formula,car was tight and rock solid as was my '82 with
86,000mi but by the time several years of winter driving
flex was noticable at 100,000 fixed it in '94-95,rigid
since
some of my other non-third cars have chassis flex too:
'84 amc eagle wagon-worse than a thirdgen
'81 porsche 928-german engineering and cost $40,000
new-could use SFCs
'68 roadrunner -chassis flex and "doghouse shake"

FireInMe17

What are you guys talking about "dog house shake"? Never heard of that before....

8t2 z-chev

not sure if that is any "offical"word,but that is what i call
flex and shake of the front clip structure drive a stock
third(or an old torson bar mopar)with the hood off,
drive over rough uneven terrain,and watch the radiator
support move and shake indedendant of the cowl
(firewall area) A 3-point STB,extra x-member(s) or
shock tower to firewall brace(like a '71-73 mustang)
will cure the problem

FireInMe17

Will that make the steering shake pretty good? Mine gives me weird vibrations when ever I drive it, even on nice roads, and it was never there when I got the car nearly 20,000 miles ago.

ls six

I think you got the cause and effect backwards on the sail panel cracks, look into the history of the airliner and you'll see refferences to an olde jet passenger jet called the Comet (mebe meteor, been a while since I caught it on the history channel) it suffered several disasterous crashes in it's early years that were a complete mystery until they discovered stress cracks around some of the planes windows.

The diagnosis was that the plane had been built with square windows, since the entire fuselage is a stressed element in a plane the forces collected at the corners of the windows causing cracks and eventualy complete failure.

A radius at a junction reduces/redirects stress lines and makes a structure less prone to cracking, we see the same principal in action with filleted cranks and welded joints.

The later A/G bodies have this exact same problem in high powered or rough service situations. And thats with a full frame! I dont know about anyone elses but my car (hard top btw) not only has the cracks but diagonal ripples running from the cracks back and down toward the fender.

This indicates to me that the area is being over stressed by either engine torque input or suspension energy input.

BTW, if that white iroc iIS running 10's then it's caged, cages are rarely structural in effect but givven the obvious lines of force involved in these stress cracks I imagine that any 6 point cage or better would have an effect on atleast the beaming stregnth of the car.

pgh1992

Is the weld-on kit better than the bolt on kit? Or do they function the same?

ericjon262

very good point. I would have never thought about it like that.

JamesC

iTrader: (5)

Most members would recommend the weld-ins.

JamesC

1BADRZ28

iTrader: (2)

mister_hudson

iTrader: (3)

For the most part they function the same. If you drive hard the bolts will come loose after a while. You can always have the "bolt-ons" welded to be safe but then you may as well just buy the welds and go that route... Weld them in and forget about it!

KITT1983

iTrader: (3)

any updates?

Pablo

iTrader: (1)

Thank goodness there is at least one voice of reason in this thread, 1MeanZ

The idea that SFCs are absolutely necessary is a total myth. There are and have been plenty of very fast Thirdgens without SFCs. In fact there was a member on here named ZZ3Astro who used to lift the front wheels on the street with a blown SBC, T tops, and no SFCs.
Furthermore, with respect to the drip rail crack, the forces imposed on the vehicle structure from a hard launch are working to push that area of the car closer together. If you look at the two sets of wheels as the ends of a bridge you will see that suspension loads from bumps in the road, etc are what are working to pull the car apart. When the rear axle is moving forward it is acting to push the car together, if anything a very hard launch would cause buckling issues. This happens to G bodies in the quarter panel area. In addition to all of that, it is quite easy to generate forces many times greater than a drag launch by simply driving over a pothole. My Buick has cut a 1.54 60' foot pulling a wheel off the ground and that didn't feel as violent as some potholes I have hit.

I too have seen the drip rail cracks, not only on a thirdgen, but on my Turbo Buick which is a full frame car. When I personally repainted the Buick I discovered that this area of the car has a large section of lead filler metal ostensibly to cover the weld that holds the roof. Couple this with the sharp corner that is a stress riser and a metal that does not have very good tensile strength, well then any flex is going to cause a crack. I'm not surprised to hear that there is similar funny business going on in that same area on a Thirdgen.
The other supposed "benefits" of SFCs are more than likely imagined than anything else.
There are certainly handling benefits but unless you have data to back up your claims you really don't even know if you made the handling worse with SFCs. Look up project Mont1go from Hotrod magazine from the late 90s. Their handling went out the window when they installed sfcs because the flex in the chassis happened to be working with the suspension. A go kart uses chassis flex to essentially be the suspension.

What I would really like to see is some data. No one has ever provided one shred of data to show how much flex is being reduced by sfcs and where. If you do a search on the net, the only article where they try to quantify the effects of SFCs is on a late model mustang. They couldn't measure any difference on that car before or after http://www.musclemustangfastfords.co...ang/index.html
If someone would do a similar test and report their results I think we would be way further along than the same hearsay over and over again.

Now don't get me wrong, I am not against SFCs. I suspect they reduce chassis flex enough to improve handling on a vehicle set up to take advantage of a stiff chassis. I also wouldn't doubt they strengthen the structure. What I want to know is how much. After looking at the chassis like a bridge, reading some SAE paper data on foam filler placement, etc.. I think that just an SFC is not the great benefit people hope.

I think reinforcing the roof to floor connection will yield greater results. Indeed the SAE paper I alluded to talked about having the greatest benefits when foam filler was used in the a pillar to roof structure section -albeit on an SUV

I wouldn't be surprised if adding the T-top/convertable door strikers to a hard top would have as much of an effect.

Anyway I just want to see some numbers. Everything else is just an opinion really.

KITT1983

iTrader: (3)

pablo you got to stop stocking me

ls six

If you actualy look at the cracks you will see that they are largely the result of the compressive forces you described, just because it's a crack dosnt mean it's the result of the metal being pulled apart.

I'll be designing a set of SFC's for both my TA and my Mazda, I'l do before and after tests to determine how much each car flexed before and after so I'll havs some relevant data to show.

I suspect on the TA especialy I'll need more than the simple bars most companies sell, something more like a truss system under tha car that ties as much of the chassis together as possible.

I have also been thinking about sheetmetal type reenforcements.

It's something I picked up from a Japanese tuner who builds wicked fast time attack cars, he'll take a new body in white and rather than weld SFC's and a cage in he'll start off by ordering replacement rocker sections and instaling them over the originals.

Then he fabricates sheetmetal "buttresses" that box out the rest of the unibody in specific areas, the result is a semi-monocoque structure. The design adds relatively little weight and makes for a supremely stiff chassis, and this is with cars such as the Honda S2000 and RX8. Cars that many people consider near perfect stock.

This requires quite a bit of work obviously but if people are genuinely interested I would happily sell kits.

btw, weld in SFC's are typicaly superior because they provide stiffer mounting to the original chassis where the bolt on type have one or two points of contact that unless doubled up can result in a pivot point rather than an integrated load bearing structure.


I would like others to look at the floors of their cars as well, i just stripped out my carpet and noticed creases behind the front seats just inboard of the rockers, looking at the car as a whole it seems as if it has been supported in the middle and bent down slightly at the ends.

It's been stock except for tires and wheels as far as I can tell, so i doubt it's from agressive drag launches and such but I'm wondering how common this is.

radical82

Very good point, ls!!! I'd suggested in another post that before you start on your next 3rd Gen project, a trip to the rack to have everything checked and tweaked back to spec might be a good idea!

Most of the aftermarket pieces are designed for ease of installation, unfortunately that may not be the best way to address the flex situation... But, as was said at a SEMA seminar I attended, aftermarket parts, other then those for hardcore racers, must be designed so Joe Average working in his two car garage with a $250 set of Craftsman tools can install them....

I like your ideas in the post above, and have been using some of those methods on unibody cars. Got a couple new ideas going in my '82, I'll post them as time and progress on the mods increases, but I will say the tub has some good points and a lot of bad things designed in to it for lowering production costs and making the car comfortable for Grandma to drive...to really optimize the potential of the 3rd Gen takes some serious design and fabrication work. Anxious to see some of your ideas!!!!!

Guest

Actually according to the table they put up, they did measure a difference and called it insignificant because they made their % margin of error larger than the % change in the numbers. If they really are that lame with a caliper, maybe they should not have bothered even taking a reading. If you look past their stupidity, the numbers are there for you and on a chassis that is a lot better (and newer) than ours and with only the chassis weight causing the difference not a road impact. The type of 'testing' they did is only used to gauge the effect, not to quantify it. You'd need to drive the car to do that.

The sail panel roof corner is not the only place these cars crack, its only the most obvious.

I'm just going to avoid the rest, as usual a whole lot of biased personal opinions floating around out there.

ls six

And how do you come up with a margin of error with only 2 data points? (ie one measurement before and one after) If one wanted to come up with a "margin" they whould have to pepeat the test several times, either with many cars or by taking repetitive measurements on the same car both before and after so they could average both groups of numbers.

Either having multiple people taking each measurement to rule out human error or repeatedly setting up the car before and after the instal to rule out differences in the setup procedure or both are a good idea but most vendors/mags/ suppliers etc dont have that much interest in producing even pseudo scientific results.

Guest

Obviously they did not really care to know, in fact I'd say they were more interested in a specific outcome and using a paper clip and calling the results statistically insignificant were just the means to an end.

Someone really needs to track down that supposed video of strut tower movement.

Guest

In case the original poster was scared off by nonsense...

You do not NEED sfc's for your frame to handle the additional power you're going to throw at it, however it is not going to hurt to put them on and its certainly going to stiffen up the already flimsy chassis these cars came with new.

ericjon262

just a thought, with a more rigid body (SFC's), I bet he would have gone faster, because more of his power would go to the wheels, and not body flex, how much is hard to say, but I bet it would make a difference.

1MeanZ

iTrader: (9)

please explain to me how body flex is eating up horsepower slowing the car down.... I'd love to hear your explanation of this....

exarkun1178

great thread.

im struggling with what to do here. my whole build is about weight loss. more importantly losing all available weight.

it will be solely an auto cross car where suspension is essential. will the added weight of the tower braces and SFC out weigh the body flex on a road course?

that adding foam thing got me thinking. though foam will still l weigh more then no foam....

ls six

Torque technicaly but he's right. Anytime work is done energy is consumed (converted actualy but same effect) and cannot be used for any other task at hand.

Deflecting a structure takes energy, that much is obvious. If said structure is more rigid then a given input will deflect it less but more importantly it becomes a more effective conduit for the transmission of energy.

It's very similar to electrical power and the resistance of the conductor, higher resistance results in less power reaching the end point and more power being lost as waste heat.

Now if the question is will the guy actualy go faster with a more rigid chassis then thats a tougher answer.

There can be too much of a good thang and that includes power to the wheels, if hes really that fast then he'll likely need to do some tuning to get the best results.

ls six

people can debate about needing SFC's on stock cars all day long but when you throw big tires and a stiff suspension on one of these cars the flex WILL become much more noticable. The inputs to the chassis become magnified many times over.

You'll never be able to tune the suspension accurately when the platform is essentialy a giant variable rate spring with no dampener.

jj74sd455

i love my subframe connectors, big difference in handling too

exarkun1178

thank you. hate the idea of adding anything but lightness... this may however make the car faster then the absence of its weight would

1MeanZ

iTrader: (9)

If you're that serious about autocross, then put race seats in the car with a 5pt harness and a roll bar and don't use SFCs. You'll want a good race seat, many of them don't recline, so you'll need a roll bar for roll protection on the street or track. a properly installed 6pt roll bar will be stiffer than SFCs by a long way.

I disagree. Using your logic, in a drag race scenario, the body will only flex to a certain point then it will stop deflecting. Then when the body uncoils after launch the stored energy from deflection will be released. The net effect lost is 0.

In the real world, the car doesn't flex enough to soak up any measurable amount of torque. I don't see how a flimsy structure absorbs a measurable amount of power.

1MeanZ

iTrader: (9)

Care to tell us how you arrived at that conclusion? Do you THINK it handles better or is there some measure of proof you can provide...

I'll back off this when people stop posting conjecture and half baked theories. This is supposed to be a technical forum, not a bunch of rumors convincing people to spend money on stuff they may or may not need.

Do any of you guys see the difference in making a fact based decision vs blindly following what someone else thinks is true?

exarkun1178

i have a one seat http://www.summitracing.com/parts/SUM-G1100/ for the car. and will be putting in a harness. still working on cage ideas. again torn between adding the weight of cage v. using existing points to mount/ single harness bar.

some people say the cage does stiffen the car. an equal number says not at all.

Guest

Is this your opinion of what happens? Zero loss?

1MeanZ

iTrader: (9)

The body deflection does act like a spring. It will load and deflect an increased distance at an increasing rate like a spring. It may or may not be linear, I have no idea. At any rate (puns intended lol) the body deflects to the point that the acting force becomes equal to the cars resistance to deflection. Then when the acting force is decreased or removed, the car has to rebound and return to normal or near normal shape. I do not know the elasticity of deflection but it would guess that it is nearly 100% My opinion is that the deflection distance is not far enough to rob the car of any forward motion, and the deflection also has no effect on the power output of the vehicle to the ground. In other words, I don't believe for a second that the car gets faster in a straight line if it is deflecting less due to SFCs. In a performance handling situation, body flex is undampened motion and it affects the car's stability slowing a lap time.

Again I want to make the clear distinction that a measureable amount of acceleration power is not absorbed by body flex. If the body twisted up 6 inches, or if the rear suspension could deflect by a couple inches it might rob the car of forward motion, but that would be the only way it would slow the car down. It would be similar to how popping a huge wheelie slows the car down. Chassis flex is not a parasitic power loss.

Guest

There are top fuel teams that disagree with your statement about flex not having an effect on ET. The appropriate question is, where is the line between too much flex and the additional weight of the SFC slowing the car down.

articwhiteZ

iTrader: (56)

I can tell you, that SFC's work, plane and simple.

they Keep the car from twisting it's self to death over time.
i have had a set or good SFC(South Side Mech) on my 92 Z28 the week it came Home from the dealer. and after 17 years of car shows and drag strip passes, looking at my car nexed to other 3rd gen camaro's that do no have SFC, there is a big diff in how the cars Feel and drive.

Linginfelter who did the stage 5 upgrade to my Z28, back in 93
also feels cars with sticky tires and Real HP will twist and flex the body to Death over time. doors dont close, windows dont seal, tops leak, the cars can feel sloppy over time. like driving a soup sandwich,

adding a rollbar to a car with a flexble body pan might help, but boxing it in with SFC, makes it even stiffer then with out.
i pulled out over 400lbs from the car and the bars and SFC only added back 200lbs. so you still save. and i still have power windows tilt. CC.

if its a car you plan on keeping for a life time, and thrashing on it. i would add SFC's, some guys will say you dont need them, bla bla bla, i say, sit your car nexed to mine, take them for a drive and see how they feel, then try to say THAT!

you can tell from how the doors close, to how the car rides, SFC's work,plane and simple.

1MeanZ

iTrader: (9)

I think my post indirectly addresses that. I do agree with you. From above "My opinion is that the deflection distance is not far enough to rob the car of any forward motion".

I think in the cars we're dealing with the amount of chassis flex that begins to inhibit forward motion is not present.

Guest

Probably true. Hard to say where the dividing line is, as far as drag racing is concerned. If I had to guess, its probably around the point where a normal suspension car is lifting the front tires off the ground. Might not be of much benefit on a hardtop car to a SCCA rookie driver who has a lot more to gain from driver skills than the cars ability either. Not like we're driving Fox body Mustangs that are about as stiff as a wet pretzel, that benefit from anything that adds stiffness to the frame.

I would say though that racing/sanctioning rules aside, there is not much point in calling them useless. These cars flex, way too much IMO. The roof cracks, whether they originated from a poor weld or not, are very telling. Either it is poor manufacturing, or poor design. In any case, there is too much stress traveling through that point of the car for the body of the car to handle. Worse yet, that is not the only part of the car that damage is apparent over time. Having installed them, the improvements in the car far outweigh the cost concerns. The only reasons IMO not to run them are if you have weight concerns, or your racing rules prevent them from being used. I can say that the vert SFC's were even put on some hardtops used for racing and called a factory part to get around the rules. So a useless part they are definitely not.

radical82

Probably the best explanation in the entire thread! Formulas, measurements, and theories on suspension geometry and dynamics don't mean a thing unless the chassis is rigid...

Not an issue on a daily driver type street car, but when you start getting into performance issues, a rigid chassis should be of primary consideration.

1BADRZ28

iTrader: (2)

I can give you real world data. I had a 10 point cage in a 1974 Nova with no subframe connectors on the car. I cracked two bellhousings over one year.Solid mounts yo frpnt and a ploy in the rear. The car never lifted a tire on the launch. Cars average run was 11.7@118 before sfc's. I finally added stiched in subframe connectors with nothing else done, the car went an average 11.45 @119 and started lifting the tires slightly on the launch I never broke a bellhousing again. Can I get an explanation? I just added 30lbs and went faster on average. I guess after that I was sold on them for all unibody's.