RevGTO

iTrader: (12)

I had 'em on each of my quarter panels before SFC's till I got 'em PDR'd. I got SFC's & they didn't come back - I just got new ones ON TOP of my quarters.

z_speedfreak

iTrader: (3)

got no dimples on my '96, altho the rear quarter panel has started to sag a lil bit, under a 1/4" but its enough to bug me..
but i did put some good ripples on my old 3rd gen with a whooping 200hp right up the rear quarters and up the B-pillars but that was a 3rd gen..

trackbird

iTrader: (4)

My 3rd gen had cracks 4 to 6" up both A pillars (right by the windshield).

Awake455

OOH! Don't forget that high quality 10 bolt rear axle, and restrictors in the clutch hose.

2002_Z28_Six_Speed

iTrader: (19)

My door must have magically misaligned themselves then. Mine hit on the striker. There are small pieces of the fiberglass missing

All I know is that the unibody does flex. I don't know an exact number or how important it is but it does flex. I have seen how much the floor flexs when you step on it with your body weight.

Tie a string from back to front on some mount points. Now, jack the car on one corner and I bet that string will be no where close to taunt anymore!!

Foxxtron

iTrader: (1)

Of course this is a joke, because that doesn't do anything to the string. I've tried that before everytime on the same two 4th Gen f-bodies I still have after 5 years (street car/part time AXer) and one for about 12 years (track vehicle) and it results in nothing with the string and I haven't been particularly nice to either vehicle (because I bought the cars to perform, not to treat like babies). That technique works much better with cars mostly of designs from the 1980's and earlier, even if they're box or tubular chassis. Today, there are many monocoques that are more solid than their tubular chassis counterparts from decades ago. The biggest problem the monocoque design suffers from is that it isn't a very efficient use of material with concerns to weight.

Yes the body flexes, just not as much as people are reading with their booty dyno, or for the matter of fact if they would reach out and hold onto the areas with their hands while the vehicle is in motion (DO NOT DO THIS UNDER ANY CIRCUMSTANCES). It's measured in Nm/degree and it's minute to the point that strain gauges with real time data acquisition is required in order to get an idea of how and which parts the monocoque have their weakest points. When performing this, the variables should be with SFC's and without SFC while all other controls remain nearly constant, of course all while operating the vehicle within a closed course.

mitchntx

iTrader: (14)

Jesus! How much do you weigh?

I weigh 275 and crawl all over a stripped interior installing a roll cage and don't see or feel the floor pan buckle.

Look at the channel a typical SFC sets into. Just ouboard of that are the door sills. The door sills are comprised of multiple layers of metal all overlapping and welded to gether. It runs the length of the body. It's argueably the strongest part of the car body. Cut one open some time. It has 4 layers and 5 in some places.

That IS the SFC. Installing another one just adds weight.

Silver02TA

iTrader: (6)

i have a couple fender demples on the driver side rear. SFC are in the garage fixing to be put on.

2002_Z28_Six_Speed

iTrader: (19)

Strip all interior. Remove T top. Step on area behind where driver's seat was.
It doesn't buckle. It deflects. There are many spots in the car like that.

Why is everything on this site an on-off logic? No one sees small changes just large ones or none.

2002_Z28_Six_Speed

iTrader: (19)

What the hell are you talking about? I was just saying use the string as a measuring device. Under slight cornering force, simulated by jacking one end of the car up, the string will no longer be taunt indicating that a change in geometric relationships between areas of the car has changed. I never said how bad it was or the magnitude to which it could affect your steering or stability going down the track.

I just inferred that it probably wasn't good and could lead to other issues.

Foxxtron

iTrader: (1)

I am talking about how it's actually applied and not what you're contriving. The force applied while lifting one corner up with a jack is not the same as the vehicle taking a corner. Even so, I have tried the same thing you are mentioning for many years and it does nothing with the string that the visible eyes, ears, and hands will detect.

Again, you need strain gauges with real time data acquisition to reveal the torsional stiffness that a whole lot of non drag racers are so paranoid about.

And Mitch is right about what he's doing.

Foxxtron

iTrader: (1)

You really need to be aware that you are the one not making sense. Myself and mitch have done that and guess what? You don't see the deflection or the bending under a specific applied load of even 400lbs. You need strain gauges for that again. Heck, I even applied olympic wieghts in that spot and the floor still didn't deflect to the point of "the dyno of human feel." With the weight of most drivers here, it's too minute for the human senses.

AFA buckling, again you need strain guages for a vehicle like this as well. unless you would like to apply the force several thousands of lbs. higher than what you'll ever see in cornering and you'll really see the jointed areas buckle like crazy.

And yes, both of my cars are T-tops.

2002_Z28_Six_Speed

iTrader: (19)

Friends, huh?

Please do make statements to attack another person. Let's keep to objective conversation. I don't understand why you keep attacking my supporting details. All I orginally wanted to say (if you look up. Please do.) is that these cars can obtain damage which is well documented by the dents in fenders or misaligned doors. This is common in unibody cars anyways.

What is your opinion on a drag car? Do you not see torsion forces as high as 1200 lb likely? When I go to the drag strip I see cars rear up on an axis from the right front wheel to the left rear wheel all the time.

All I am saying is that the forces produced from turning, accelerating, or braking are enough to alter the unibody given that from the A post to the rear end its structure isn't designed to resist torsion loading.

I DIDN'T SAY IT BUCKLED or any of the sort. I just said forces common to these cars could deflect the body's structure well under the ultimate tensile strength and then return to its normal position. I don't see how you could argue that.

You do not need a strain gauge to witness bucking as you have eyes. For testing forces which do not approach the necking down region as you suggest but I did not lead up to... yes, you do need a strain gauge.


Summary: The body can be deflected and return to normal.
Other thought: I don't see why since there is no play in the componets attached to the body that a deflection in the body could cause damage to a fender or misalign a door.

Foxxtron

iTrader: (1)

Here I go,

FWIW, mitch and the others are...

Mostly strangers to me, however from what they have experienced, they have pushed to f-body to very serious limits. AFA the supporting details, unfortunately they don't. The damage seen is mostly from other things and if you do a search on mitch, trackbird, Cal and Sam, you'll see what they've done and what they do. The dents and other damage you mentioned are acutally poorly documented, because unless they never see a parking lot, those dents are entirely possible. Not one SFC on the market ever reaches the point of the rear end of the body where everyone complains about.

AFA being common in monocoques, is very untrue because if that was a fact, then how many exotic vehicles and professional open wheel cars and prototypes don't have any evidence like this? I also have seen this on tubular steel frame cars as well.

An interesting example of this whole "weak stamped steel" and "strong tubular structures" would be the factory K-member vs. many aftermarket tubular ones. I have had three tubular K-members, all which have failed in several locations, not to mention the drastic reduction of front end stiffness introduced through running the tubular K-member. Both of my stock K-members haven't failed at all. The majority of stock K-member damage on a 4th Gen occurs because there is a heavy collision involved, e.g. running into a safety wall and less a situation of running up on a curb. It's more than just tubular frame vs. stamped steel. This K-member is very important structure as well.

If the wheels lift too much off the ground, they're launching wrong and if they don't have a cage, they're being suicidal. Again, you don't see exact numbers with your eyes.

So have you done what I've done with the vehicle you have posted? After all, I can tell by what parts you have installed that there is very little possiblity what you explained could have occured. You introduce the tyre jack, but you don't introduce frame measuring machines, which are the least you can measure these changes over time and those are only part of the battle.

Can't tell that with your naked eyes, and with what you mentioned, that test with stepping on the floor panel with the T-tops removed cannot be accurate if you performed like I think you mentioned it. The string test is really not accurate at all either. Again, you have to perform this in a real-time environment that will go above and beyond what you're mentioning. I should know, because a third f-body of mine was recently put through rigourous testing beyond what many auto manufacturers put on their vehicles. I assisted my friend with his completion of his Master's thesis by torturing this specific test car and I was operating with some very high spring rates and valvings to match, much higher than what can be operated on the street, and there were many bumps on parts of the courses we set up (basically lots of very high speed bumps). I have even installed SFC's on several intervals and removed them as well (thanks to a MIG welder and Plasma cutter) and there is not one difference in the results.

Like we've said before, you'd snap the TA or the rear end before that will happen. Besides, what exactly have you done with the vehicle. I have a 94 that's never seen SFC's but have seen lots of Drag racing, then Open tracking. There are none of artifacts that these crazy testimonies want to mention. AFA testing forces are concerned, they are way above and beyond what you assume and to the point that's beyond many occupant's threshold of tolerance.

Not to the point of your eyes, ears, and hands can detect. There is not enough movement when operating the vehicle with even the most spirited AX than can even come close to doing what your mentioning.

If the body would misalign, the strain guages would be the first to easily detect it for before your eyes, ears, and butt would. Interior cameras are poor at this, because they are mounted in such a manner that vibrations will affect the stability (no matter how it's internally mounted). These cars are not "flexy fliers."

What kind of seats do you have installed? How old are the bushings? What kind of Hp are you currently running? How long have you owned the car you mention? How many others have you had in your long-term possession? Do you know your precise spring rates?

Jon A

Foxxtron, really, I love you man, and I hate to butt in without anecdotal parkinglot tales or completely meaningless strain gauge data, but for the love of God you are making my eyes bleed! I'm trying to look away, really, I am. I'm too busy to be spending my time looking at these accidents. But in hopes it will help some people:

If this is a subject you'd like to educate yourself about, I'd suggest starting with papers like THIS for starters. If you think these cars are better than the baseline case with all of its "problems" in the above I've got a really nice bridge for sale.... Measuring the torsional stiffness of a structure with a couple strain gauges randomly stuck somewhere is akin to measuring the windspeed by licking your finger and sticking it into the air--you had better have about 50 pages of analysis or a complete FEM with about 20 pages of analysis with which to relate it to overall stiffness and a means of validating that relationship or it means nothing.

You're trying to infer a much more global property by measuring a local distortion. If you don't know exactly what the structure is doing, every single piece relative to one another for a given load, you're pissing in the wind. You'd be much, much, much better off with a jig, a crowbar, some weights and a tape measure. Actually directly measuring what you're trying to measure instead of infering it from microscopic strains in pieces of structure you may not even understand.

Could somebody please point me to the source that teaches if something doesn't break it must not be flexing at all, EVAR!?! That's enough to make any Engineer, or anybody who has actually measured anything . Because we all strive for structures that flex the least and even when overbuilding them many times as "strong" as they need to be (and really, really, heavy) they still flex. And yes, significantly enough to affect performance in applications such as this. I really do wish avoiding it was as easy as you guys want to think. Unfortunately the reality is quite the opposite.

1QUIKWS6

iTrader: (61)

Well, what we need then is a concrete scientific explanation for the IDENTICAL dimples that happened to show up on the top breakover of each rear fender almost directly above my rear wheels. They were not present when the car was new.

My car has NEVER seen a parking lot (unless you count the times it's at a car show and I'm sitting 4 ft from it at all times). It is also quite impossible to get a door ding in the area that these dimples occurred and there was no paint removal.

All I can atest to is that after I installed the SFC's, and had the dimples fixed by Dent Wizard, they never reappeared and this along with even higher power available than when they first appeared, and the fact that I drive the car much harder.

So until someone can actually prove that these dimples are not body flex related (by modeling the car completely in 3D and then conducting an extensive FEA analysis) - I'm stickin' with that theory...

Foxxtron

iTrader: (1)

FEA cannot always suffice solely on it's own when it comes to the actual complete outcome. It is more of a "calculator" of sorts than one of true occurance, and a very accurate one at will. I am a materials scientist and I use FEA quite often, but the problem is that FEA is propagandised as "solid proof" when in acutality it's one of several instruments for analysis, not one of absolute determination though it's awfully accurate. In the end, what happens on paper or computer doesn't always match what occurs with the operational prototype during test runs.

What happens with the dimples should be more from the springs on the rear than the strength of the floorpan. The dimples above the rear quarter panel mostly come from...

The factory. I have even seen several in a lot of new ones with those dimples. It's a manufacturing defect. There are ones with them, and ones without.

Also I know of 28 cars that have SFC ever since less than 1000 miles, yet all developed them afterwards. Their Hp ratings are from 300rwhp to 750rwhp. This opposite example still doesn't solidify what's happening.

Foxxtron

iTrader: (1)

Dude, I understand, but I actually have read that journal, and I am performing partially what's there. What I'm telling people here is that there is much more than just strings and jack tests. Strain guages by themselves are not even anywhere close, but much more closer than what's been stated around here. I have and am doing much closer than what you have assessed with what I typed. I am not just throwing random sensors in random locations on a vehicle and running around with it and just coming up with some complete and absolute number without some effective pre and post trial analyses.

If you read what I stated earlier, I stated that the body does flex (deflect rather), but how in the world does it flex to the point where people are seeing it and with what simplified tests they're performing. Some do, some don't. Some will not fail while others will. Also I NEVER stated at anytime that if the structure severely bends it must break. Many structures like that won't, including buildings, bridges, and other structures of civil/structural engineering. NEVER. I stated that there is much more than what meets the eyes. But once again, with what many do here aren't like what you do either.

But how in the world can the SFC's like you have, and I have had significantly reduce what is being complained about here. This is what I'm am trying to figure out, especially since the human senses cannot easily do it.

All chassis have some deflection to them. What I am trying to figure out is how in the heck are all of these tales of extreme deflection that's visible to the naked eye happening? Where then Jon? I am not being sarcastic, just trying to get to the bottom of it.

In the end, it's a foregone conclusion that people will do what they want. I just think that there is more than just "it's gotta be chassis flex cuz it's a monocoque" argument. 4th Gen is far from perfect, but is it really as bad as people make it here?

But I have a question Jon. In the end with performance concerns, am I just realising that I am imaging that SFC's are actually increasing performance considerably? Because if it is, I am not recording any significant differences in lap time. Every little bit helps, but from what I am noticing, it's more hit or miss and the hit or miss probably has much to do with factors other than the monocoques rigidity.

P.S. I currently run the practically the same spring rates you do as well.

johnpate01

iTrader: (3)

Here is something to try. While driving, or someone else is driving, try to put your fingers into cracks, such as those between the t-tops and the body, or the back of the door near the sail panel. Then turn a corner. I know that I can feel a pressure change, like the chassis is flexing. But, I am not that concerned about such a small change. They chassis WILL FLEX SOME. It just will. But it is not even close to being noticeable for most of us out there. It really is a nonissue for all but the must hardcore or us out there, in my opinion.

Demon Of Dreams

iTrader: (3)

just going to put my few pennies in...

when I got my SS it had 13,894 ... was a garaged car and it was shipped down to Houston from Seattle... after it was washed and waxed, though it had a few swirl marks, I inspected it with a fine tooth comb... I had no markings, dimples, dents, dings, whathaveyou anywhere... 5000 miles later at 18,800, I am only now putting SFC's on the car. Unfortunately I wasn't able to order them when I bought the car due to some unexpected financial difficulty. That is my one biggest regret. The roads around houston take a huge toll on these cars, especially since I'm not doing a lot of highway driving (maybe 1500 of the 5000 are highway miles, trip to austin, galveston and brownsville and back) ... I do not have door dings, I make sure of it... there are no paint transfers, nor anyone who will be near me in a parking lot as I park in a spot with about 8 feet on either side of me where no one else can park :o

but I do drive the car hard, and unfortunately, it is driven on some very shitty streets.

and because of this, I do have a few of the dimples, and I am not happy about it.


for the naysayers out there, don't call the lot of us liars because we have "door dings", because these dings are nowhere near doors for the most part, unless somebody is hanging out of a window and hitting all of our cars with a stick or something...


of course it does depend on the car... some of these cars are stronger structurally than others. That's a given.

SFC's are just another form of "preventive maintenance" ...

coming from the thirdgen world into the fourth, you can tell me all you want to about how these cars are built and what they're designed to take... but I'll tell you right now, give them a few more years, at most the LS1's are 8 years old. If you think these cars won't loosen up and tolerances won't change, then by all means continue to beat the **** out of them the way you have..

but for those of us who love our cars and want to use them for just a bit more than stomping into the ground, just shut the **** up about whether or not SFC's do anything.

Fact is, they do, and over time and with previous results, you really cannot argue it in the long run because just like the thirdgen, when these cars hit that certain age, they'll be the same way, and we'll do our best to keep it from happening.

besides, its not your car, so keep your banter to yourself if you want to go judging what somebody else does.