drag1LE

Recently put a 10-point in my car. Does that negate the need for SFC's?

I'm planning on going with new LCAs and relocation brackets (to try to help with my hook) and am wondering if SFCs are redundant with the cage in.

Thanks.

AC

iTrader: (3)

Drag1LE, no it doesn't. Of course the cage is helping and doing something to stiffen the frame but at much different points on the frame than the SFC's do. IMO I would've gone SFC's first then if I got REALLY spunky I would've torn the interior out to weld in a cage. I think with a wonderbar, strut-tower and LCA's you could achieve a great deal of frame strenghtening / twist resistance.
Is your car streetable or is it a track car?

MrDude_1

LCAs ARE redundent if you have a full cage.
they'll just add weight, and the car doesnt get any stiffer.


ive seen this personally on several cars... and its one of the reasons i didnt want to put SFCs on my own car... because i knew id end up with a cage in it.

AC

iTrader: (3)

MrDude, you said LCA's are redundant...or did you mean SFC's? How could they be reduntant if their tieing different areas of the frame together? I know the unibody is connected to the frame but I'd think they were strengthening in different areas in their own respect.

drag1LE

Street/strip car. Needed the cage to pass tech (bottle-fed 388).

AC

iTrader: (3)

Drag, Ahhhhhh, that makes sense. If I ever make it to the track it will be for a 1 pass, get my slip, and get banned forever from that track. I'm sure my car will run in the 11's on a good tune. I've had some say possible 10's with slicks but I'm not going to try because my luck I'd run 10's and wreck either my car or accidentaly hurt someone else.

MrDude_1

i ment SFCs.. heh musta had a brain fart.. LOL.


they really arnt strengthening different areas.. the unibody IS the frame..
the only reasons SFCs "connect the subframes", is that thoes are two stiff structurally sound parts of the car... you're connecting them not to have them tied together, but rather, using them to try to stiffen the floorpan from flex.
note, most SFCs dont really even do much subframe bracing... they run along the edge of the floor pan to stiffen it... and use a small arm to brace on the front subframe.. the rear sticks to the lower control arm mount.. not the inner subframe.

when you put a cage in, you now have a big stiff 3D (not flat bars) steel structure.. holding the body in place in those areas... it makes it ALOT harder to twist then subframe connectors do...
adding connectors, will not stiffen up anything in comparison... and ends up doing nothing but adding weight... and on most cars that need cages, they want to keep the weight low for racing

AC

iTrader: (3)

MrDude, nice explanation. Makes sense to me

AlkyIROC

SFC connect the front and rear subframes together. A roll bar/cage stiffens up the chassis but it's only attached to plates that are attached to the sheetmetal floor.

You should have both. They do different jobs.

AlkyIROC

Not mine. Mine run roughly under the seat(s) and are welded to the ends of the front and rear subframes. They were custom made by a local chassis shop. Personally I don't like the rocker panel SFC style since they don't really tie the subframes together properly.

Shagwell

I agree with Stephen, you need both. Sfc's will help eliminate twist, which a cage will do very little for.
- Think of it this way, with the main hoop welded in place, how hard would it be to twist(from side to side)the a-pillar pipes from the bottoms, even if they were tied together? - not very. A cage alone doesn't do much for the torsional stress involved in a good launch.

Even if you had a full cage with an x-brace, the center of the car would still be prone to twisting on launch.

drag1LE

Thanks all for the advice. I really need to get this thing to hook.

Last time at the track, I ran an 11.35 @ 128 mph. With a 1.9 60'

Imagine where the ET would go if I could pull a decent 60'.

MrDude_1

bull fu<king ****.





you know, i could see Stephens point if hes talking about the force of the car going forward, and wanting to tie the push on the rear LCA mount, into the subframe at teh front of the car.

but you talking about a cage not being stiff, is just plain bull****.

honestly, id go into it, but really, it would be a waste of my time. you're just going to keep spouting off crap on the board from **** you read earlier on the board anyway..

83 Crossfire TA

iTrader: (2)

That is a VERY bad idea. I understand the whole making one run and getting chucked consept, but limiting traction to keep it from being too fast is WAY more dangerous then just putting slicks on it and going for it. Typically a car as fast as you’re describing gets babied or pedaled out of the hole, and then the driver gets comfortable thinking they have traction at half track, they get into it and go sliding across the track hitting the wall or another car between the 1/8 and the finish line.

it really depends on how you build it. As long as you tie the cage into reasonable points on the floor it would be hard to do it so it isn’t significantly stiffer then stock or even with subframe connectors.

If we’re talking about an actual cage it should have down bars going from the main hoop to the LCA pickup points and a rocker bar from the main hoop to the front bar, essentially creating a structure that is a lot like a big, 3D subframe connector.

AC

iTrader: (3)

83 Crossfire, I completely agree with you. As I said, I could put slicks on it and go way fast but knowing my luck I would do just as you said and probably feather it off the line even though I could probably do a 5k clutch dump. Once off the line I'd have that false sense of off and running and nail it. After that all hell would break loose and 1 of 2 awful things would happen (we've both described them). I've built my car for street only. Yes it's track capable but I don't have track experience and I really think one should have that if you bring any serious equipment to a track. At least for the other drivers saftey sake.

Shagwell

look at what I said.
I did not say that a cage doesn't stiffen the car. All I said was that you can still twist the car in the center, so sfc's would still help. Under a hard launch the rotation of the engine tries to twist the driver's side of the car upward, the passenger's side down. A 8, 10, or 12 point cage by itself doesn't have a lot of strength to counter twist in the center of the car. YES, it does some, but sfc's still help. The sfc's would also give you much more to tie too, as 83 Crossfire TA stated. - As for force of the car moving forward, yes sfc's would still help, but the door bars would also be helping this.

-My info/opinion is from personal experience. If I don't have experience with what's being asked, I stay out or respond by saying "from what I've heard....search for X post" etc. I am a frim believer in a cage, especially after having the unfortunate event of watching my father take out 2 sections of retaining wall at 125mph Friday night, then slide over 1/8 on the roof. He is fine, the car we built held, nothing from the firewall back moved, all the safety equipment did its job, thankfully.

AlkyIROC

If you have a full frame car, Monte Carlo etc, and you install a full cage, would you cut out the center part of the frame just because you have a cage?

A third gen doesn't have a frame. Just multiple layers of sheet metal in key areas. Even first and second gens don't have full frames but at least on those the front and rear subframes were closer to a rear frame. By joining the front and rear subframes, you make the chassis stiffer and more controllable. A full cage adds stiffness to the car body but does little for the chassis because of how all that sheetmetal flexes.

Norm Peterson

The load paths get better with properly designed SFC's - with or without a cage. Every little kink in a load path represents something that's bending, which you can freely translate as another location that is experiencing higher stress and greater fatigue, as well as giving away some chassis stiffness.

Tying cage tubes to sheetmetal, even with mounting plates of the required size, is still not as good as cooking up a combination of existing chassis structure, SFC's, and cage that all work together instead of being "band-aided" on top of one other. The details matter.

A full tube-frame car would be better yet, but I think that's still outside the scope of this discussion.

FWIW, the mostly 2-D frame of the "full frame" G-bodies is nothing to get excited about. It takes less pry bar than you think to open up an extra quarter inch of clearance between the frame and the body for body bushing replacement. Even if you loosen only the bolt in the one body mount that you're replacing. Not all of this "give" is in the body sheetmetal . . . in two or three places on each side it's mostly the frame that's bending/twisting . . . typically involving the extra frame flexibility that's present where it is bent . . . which brings this right back to the concept of straight load paths . . .

Norm
(structural engineer/pipe stress analyst)

Time2Fly

To address the original question The answer is yes. Let me (someone with chassis building experience) explain why: When properly installed (read positioned), the door bars will transfer torsional stress from the front sub to the main hoop. When properly installed, the main hoop should be tied into the rocker panel and also tied into the rear sub where the trailing arms (LCAs) bolt to the rear sub. This is acomplished by the small 1-1/4" tubes that should run from the intersection of the hoop, cross bar, and door bars to the point at which the LCA bolt to the rear sub. Now, let me explain something here that everyone else who has replied is not addressing. GM produced this car in mega quantities (among other lines) without "tying" the front and rear sub frames together as you have. GM engineers tied the front and rear subs together using the floor and rocker panels. This is why the sanctioning bodies require rocker tubes if the inner rockers have been altered. Although GM engineers did not intend these cars to go 10's at 128 mph, they did expect them to be safe and reliable-which they are! They are stiff enough (untouched) for 100,000+ street driven miles. The laminated construction of these cars has been used successfuly for many years and by tying the front and rear subs together with a cage rather than using round tubing in a horizontal plane you have stiffened your car and made it safer. Obviously this arguement would not hold true if you were to back-half the car, then the answer to your question would be no. If your cage was installed correctly and has tied the front and rear subs correctly, it will sit on three jackstands-two up front (under both lower A frames) and one under the rear end housing close to where on of the LCAs bolts on. If you try this carefully, you may be surprised at how stiff you car is now.

83 Crossfire TA

iTrader: (2)

I think that we just said exactly the same thing. One thing that I would add here is that if at all possible, that front plate/rocker area tied into the doorbar in a perfect world would have outriggers under the pan tying that area into the front subframes, but in a real world, on 99% of cars you only have room to do it on the driver’s side. On the next car I do I may actually try cutting the floor pan on the passenger side and do the same mostly _on top_ of the pan to do the same…

OK, this may explain something that I’ve wondered and asked about a bunch of times that I’ve never found a real answer… by rocker tubes you mean a tube running from the base of the main hoop to the base of the front hoop or front down bars or front mount of the door bar, right? The answer I’ve always gotten about them is “it’s like hinged door bars” (no rules against them, no rules how they should be done so they are up to the inspector), in that yes, they technically are on the drawing but you don’t see them in a lot of cars and most tech inspectors let it slide.

It would make a lot more sense if it really was “well if that piece is modified you need one, like a knee bar if the firewall is significantly modified…

My next question would be why would you alter the inner rockers?

I’ve thought about actually tying the rocker bar into the inner rockers with some sheet metal or even cutting the floor pan sheet metal at the rocker and sinking it in/welding it to both, and then just carpeting over the whole deal and never got a clear answer if it would be legal… same thing with tying the main hoop into the roof structure.

Time2Fly

Yes. On cars where the original floor has been removed, they are required for certification. Good question...In my previous reply I should have stated that this bar is also required if the original floor has been removed as would be the case in a back-halved car. I cannot think of a scenario that would call for modification of the inner rocker without removal of the floor although I am sure someone else can.I always tie the rocker bar to the inner rocker with 1/8" plate material at a point where the outside seat belt tab is to be welded to the rocker bar.