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Now that thread ^^^ was super informative. Thanks, Tom.
Musings...
It left me wondering if square (rectangular, really) steel tubing, maybe 1" or (1.5") by 2", could simply be stitch welded to the under sides of the frame rails in the same place that the fancy $500 frame stiffener setup is mounted. Put on flat, with the broad side to the existing rail. This would seem, to me, to be much better and much cheaper. It would take almost zero fabrication and would add not more than 30ish pounds (at the very bottom and in the middle of the car, minimizing the effect). These tubes wouldn't effect ground clearance more than about 1", probably less, given other lower-hanging parts. Not only would the welded-on piece create single-piece continuity between the front and back of this rail, it would effectively increase the vertical dimension of the rail considerably. It would be almost entirely hidden, and would obstruct no mechanical work. What would it cost? Maybe $150? Good jacking point, too!
It's such an obvious, simple, and inexpensive solution that I'm sure someone else has tried it, or at least dismissed it as folly. It obviously wouldn't give the C4 a 2010+-Porsche-911-like chassis, but it might mitigate some of the obvious faults and provide better handling feel for those exploring limits handling.
It seems to me that the weakness of this particular span of frame rail is mostly to blame for many of the C4's faults with the top removed, and perhaps a good number of them with the top on. A simple, cheap, aesthetically benign, and substantive solution would be tremendous, if it could be found. Maybe I have no idea what I'm talking about. Long day.
It left me wondering if square (rectangular, really) steel tubing, maybe 1" or (1.5") by 2", could simply be stitch welded to the under sides of the frame rails in the same place that the fancy $500 frame stiffener setup is mounted. Put on flat, with the broad side to the existing rail. This would seem, to me, to be much better and much cheaper. It would take almost zero fabrication and would add not more than 30ish pounds (at the very bottom and in the middle of the car, minimizing the effect). These tubes wouldn't effect ground clearance more than about 1", probably less, given other lower-hanging parts. Not only would the welded-on piece create single-piece continuity between the front and back of this rail, it would effectively increase the vertical dimension of the rail considerably. It would be almost entirely hidden, and would obstruct no mechanical work. What would it cost? Maybe $150? Good jacking point, too!
It's such an obvious, simple, and inexpensive solution that I'm sure someone else has tried it, or at least dismissed it as folly. It obviously wouldn't give the C4 a 2010+-Porsche-911-like chassis, but it might mitigate some of the obvious faults and provide better handling feel for those exploring limits handling.
It seems to me that the weakness of this particular span of frame rail is mostly to blame for many of the C4's faults with the top removed, and perhaps a good number of them with the top on. A simple, cheap, aesthetically benign, and substantive solution would be tremendous, if it could be found. Maybe I have no idea what I'm talking about. Long day.
Great topic, by the way.
I think that you may be onto something. Good old "weld-in sub frame connectors". They really help F-bod's and Fox's...why couldn't they work here too?
FWIW this is how I have my car set up. I first put a vert x brace on the car and it made a nice difference. Then I bought a camber brace which helped some more. Then I boxed the x brace with 1/8 inch flat stock and was amazed at what that did. I can put a jack under one corner and lift 3 wheels off the ground and then open either door if I have to. I have just finished installing coilovers but have not had a chance to try it out thanks to the weather.
We have discussed at great length the cowl shake thing and it has been found that a lot of the older cars like my '85 does not experience cowl shake. Mine never did even with the top out, we never did figure out why some did and some did not.
At some point, I used to have the fastest C4 around.... The fastest ASP car... and I drove it to the track and home and around town on same tires...
The trick was to stiffen the frame. Adding stiffer springs, especially, to the front, made the cat feel like the front frame became the spring i.e. it would move up and down.
There are several important 'fixes'. The frame is very 2-dimensional and not triangulated. It is supposed to be a semi-monocoque with those big tubes running up and down... but(!):
1. The frame rails were spot welded. The whole idea of semi-monocoque was defeated! What looks like a big frame rail is two pieces (or more) of steel that move independently and do not contribute to stiffness. You have to weld the whole frame properly. If not then do step 2.
2. A cross-brace can be welded from front to back.
3. Belt bar and rear roll-cage connected to roll-over bar stabilizes the rear suspension. The rear bushings have to be solid. 5-link + rubber = disaster. Polyurethane makes it squeaky but not much better than rubber.
4. The roof has to be solidly mounted or the roll-cage has to have x on the roof and run down to the front.
5. Engine can be stressed to connect both sides of the front frame rails together i.e. solid engine mount.
6. Same as (5) can be applied to the 'torque-arm' (same as C5 torque tube). Note that the nose of the diff has to be supporte with any kind of power or it will come right off! at about 600ft.lbs.
See how above makes a 3-d stricture and everything is ties in.
Unfortunately, all of the above takes a lot of steel and it is heavy! The local tube-frame manufacturer said that the stock frame The frame is 900lbs! It is very heavy. Consider that Lotus Elise frame/tub is 70lbs. Long-wheel-base Lotus Elise with 400hp V6 has the same wheelbase as the C4! Almost same track, same power as the C4 ZR1 and weighs in at 2200 to 2400lbs in North American trim (It is for sale in Canada as road-legal car). The world does not stand still....
Great post...I've seen it posted before that running a bead in place of all the spot welds "helps a lot". Maybe more than any other bolt-on.
Two questions:
1. What do you mean by "solid bushings" in the rear suspension? Wouldn't that cause binding in a 5 link? Or are you talking about spherical bearings for the joints?
2. In #6, what do you mean by "same as #5"? The C-beam is already rigidly mounted to the trans and diff....and that assy isn't adding the the frame's rigidity in an meaningful way. Were you talking about using solid batwing bushings in conjunction w/solid motor mounts?
Spot welds are a disaster. They probably ruined a perfectly good engineering design.
Forgive my jargon, solid bushings=heims=spherical bearings. Solid steel would bind. that is not good.
5-link or 4-link is weaker that SLA. A-arms are triangulated by their nature,so allow less unwanted movement and more suspension stiffness. On a Lotus elise, rear lower a-arms are structural components, without them the whole rear frame would bend!
So to make 5-link as good as SLA spherical bushings and re-enforced mounts are a must.
I never liked harder Delrin bushings. They would sqeek and bind and still be too soft. Guildstrand used to make bearings for the front like Joe's and Coleman for the circle track. They are the best!
I did not find spherical bushings too noisy on the street. Polyurethane was bad....
The front of the car and the engine is a tricky area, as it is a completely open and flexy box. I used solid engine ,mounts... but I ran an iron block. The k-member is spot-welded also. The greatest C5 improvement and the solution was a single cast cradle under the motor.
Even my 2008 BMW M3 that uses a similar monocoque un-glued the windshield at Mosport on very old and re-used R6's.
I forgot the work that I did on the C-beam. Its greatest function in the stock C4 is to support the rear diff. When I made a full tube frame, I left it out. I managed to crack the diff housing nose right off on a standing start. In a more stock car the c-beam can be re-enforced and connected to the frame to be a real structural member.
Originally Posted by Tom400CFI
Great post...I've seen it posted before that running a bead in place of all the spot welds "helps a lot". Maybe more than any other bolt-on.
Two questions:
1. What do you mean by "solid bushings" in the rear suspension? Wouldn't that cause binding in a 5 link? Or are you talking about spherical bearings for the joints?
2. In #6, what do you mean by "same as #5"? The C-beam is already rigidly mounted to the trans and diff....and that assy isn't adding the the frame's rigidity in an meaningful way. Were you talking about using solid batwing bushings in conjunction w/solid motor mounts?
The real trick is not to weld over the existing weld. That will do little, maybe something, but very little. In fact, it is the wrong question to ask.
You have to weld the whole frame of the car together... or as much as You can.
The C4 frame would be OK, if it was all one piece or 'hydroformed', as in C5. In this case the spacial tube-like structure of the frame would provide a lot of strength. It is not unthinkable that the prototypes, being hand-made, were like that. For manufacturing, the frame rails were made in two parts. This would still be OK. But then it was just spot welded!!!! in a few places!!! (Spot welds are OK, especially on a production line... usually...) The other way to say it, is that the frame is not welded in enough places as in the whole length of the join between the 2 halves. And there are 2 halves on each side, so you are driving a car that is about to come apart into 4 pieces. Remember Ford minivans that would separate into front and back halves?!? (I exaggerate a little.) So the whole monocoque is not connected in any way down most of the length of the frame!!!! It is just sitting there, moving about and flexing... a lot.
To do a real job, you have to strip the whole car. Till only the frame is left. Take the frame and weld ALL the seams. In the process you would go over the original GM spot welds, mostly not to interrupt the flow...
I built a race car starting from a bare frame, so that is what I did. Took a professional welder half a day, just for the frame.. and then we added roll cage and other bracing.
I realize that not all would have the desire or the inclination to do this.
So what can be dne with the most of the car and body in place? What are the most important areas to attack?
I did the whole frame. I never thought about it the other way. I do not know. It would be a compromise. Would it be 50% as stiff as fully welded or 90%??? I do not know. i have not done any analysis. I, even, do not know where the original spot welds are. After pushing the original C4 frame to the linit with bracing and running FTD and a record for ASP, I decided that I needed something better.... But that is a whole other long story.
Anton
Originally Posted by VikingTrad3r
would anybody be able to post a picture of the spot welds replaced with bead welds? or a picture of the location of the tack welds
The real trick is not to weld over the existing weld. That will do little, maybe something, but very little. In fact, it is the wrong question to ask.
You have to weld the whole frame of the car together... or as much as You can.
The C4 frame would be OK, if it was all one piece or 'hydroformed', as in C5. In this case the spacial tube-like structure of the frame would provide a lot of strength. It is not unthinkable that the prototypes, being hand-made, were like that. For manufacturing, the frame rails were made in two parts. This would still be OK. But then it was just spot welded!!!! in a few places!!! (Spot welds are OK, especially on a production line... usually...) The other way to say it, is that the frame is not welded in enough places as in the whole length of the join between the 2 halves. And there are 2 halves on each side, so you are driving a car that is about to come apart into 4 pieces. Remember Ford minivans that would separate into front and back halves?!? (I exaggerate a little.) So the whole monocoque is not connected in any way down most of the length of the frame!!!! It is just sitting there, moving about and flexing... a lot.
To do a real job, you have to strip the whole car. Till only the frame is left. Take the frame and weld ALL the seams. In the process you would go over the original GM spot welds, mostly not to interrupt the flow...
I built a race car starting from a bare frame, so that is what I did. Took a professional welder half a day, just for the frame.. and then we added roll cage and other bracing.
I realize that not all would have the desire or the inclination to do this.
So what can be dne with the most of the car and body in place? What are the most important areas to attack?
I did the whole frame. I never thought about it the other way. I do not know. It would be a compromise. Would it be 50% as stiff as fully welded or 90%??? I do not know. i have not done any analysis. I, even, do not know where the original spot welds are. After pushing the original C4 frame to the linit with bracing and running FTD and a record for ASP, I decided that I needed something better.... But that is a whole other long story.
Anton
I really enjoyed your clear explanation of the C4 frame and it all makes sense to me (sounds like we are stuck with what we got unless we rip into our cars).
You said you needed something better and I am curious what you are running now
C4 frame progression and why you should never ever go racing
Thank You for the compliment.
When I had the mild steel roll cage welded in at CSC Racing, here in Toronto, they joked that it was 1000lbs. They were not too far from the truth.
The natural progression was to build a chrome-moli tube chassis/frame. It was less than 200lbs. Chrome-moli is great. Thin tubing requires some care when welding i.e. no fans or breezes through the shop. The car was 2350lbs, 900hp and went 200mph at Mosport back straight, when the 'hump' was still there. This car had C4 knuckles and diff housing and steering rack. The Europeans came up with new steel tube that is 50% stronger than 4130 and as easy to weld as mild steel. Technology moves on... It is easy to make something strong and stiff with structure. It is much harder to make it light.
Yes. that is a real C5R LeMans body. The aero was good.
The Lotus elise has the same suspension dimensions as the C4, especially the 'stretched' V6 cup car. It is very surprising. The aluminum chassis 'tub' is 70lbs. The Alfa 4c has a similar (inexpensive, so heavy) CF tub at 70lbs, but much stiffer. This is getting far off topic....
That is why You should never think about racing or AutoX or tracking Your car! It will lead to total ruin of an otherwise genuine character!
Anton
Originally Posted by grandspt
I really enjoyed your clear explanation of the C4 frame and it all makes sense to me (sounds like we are stuck with what we got unless we rip into our cars).
You said you needed something better and I am curious what you are running now
When you welded the frame on your C4, did you weld along the edge of the butt'ed, spot welded seam? Or did you bang the seam over w/a hammer, then weld it? Or did you cut the seam off and run a bead, joining the frame segments that way?
No cutting and no banging. Just welded all the seems and welded some manufacturing holes in the frame shut. nothing fancy. It was very stiff with the roll-cage and some frame bracing. It was just a lot of steel.
It would take a few man to move that frame. We made a dolly with some hd wheels.
Anton
Originally Posted by Tom400CFI
Post #71 is great.
When you welded the frame on your C4, did you weld along the edge of the butt'ed, spot welded seam? Or did you bang the seam over w/a hammer, then weld it? Or did you cut the seam off and run a bead, joining the frame segments that way?
When I had the mild steel roll cage welded in at CSC Racing, here in Toronto, they joked that it was 1000lbs. They were not too far from the truth.
The natural progression was to build a chrome-moli tube chassis/frame. It was less than 200lbs. Chrome-moli is great. Thin tubing requires some care when welding i.e. no fans or breezes through the shop. The car was 2350lbs, 900hp and went 200mph at Mosport back straight, when the 'hump' was still there. This car had C4 knuckles and diff housing and steering rack. The Europeans came up with new steel tube that is 50% stronger than 4130 and as easy to weld as mild steel. Technology moves on... It is easy to make something strong and stiff with structure. It is much harder to make it light.
Yes. that is a real C5R LeMans body. The aero was good.
The Lotus elise has the same suspension dimensions as the C4, especially the 'stretched' V6 cup car. It is very surprising. The aluminum chassis 'tub' is 70lbs. The Alfa 4c has a similar (inexpensive, so heavy) CF tub at 70lbs, but much stiffer. This is getting far off topic....
That is why You should never think about racing or AutoX or tracking Your car! It will lead to total ruin of an otherwise genuine character!
Anton
I'm just getting ready to start this on my track car...using a flood totaled ZR-1 for the base of the build. I'm not going to strip it all down to bare frame...but I am going to get access to as much of the seam as I can by cutting away what I can, welding and then putting those pieces back in place.
Did you strengthen the front K-member as well as the front cross-member by welding all the seams? It appears that the pieces they used could get a lot of strength added by doing this. Admittedly, for the day, these cars were top of the heap but knowing what they did shows why the C5 and subsequent generations have a solid hydro-formed frame rail...
Once you start on a track-build you start to see a lot of things that they compromised on for production...areas where they got no significant gain for a street car and so they didn't deal with it.
Areas like the front shock towers...again, spot welded and small stich-welds done where it should have been solidly welded together along every seam.
The basic principle is to weld whatever you can, weld where it is bent metal that is just spot-welded. Strengthen weak points with bracing. Buy some gassets and gasset the bends and joins where you can.
I built a stick model and tried to model the bracing.... It was a long time ago. I still have a C4 ZR-1, a 1992. I used it for AutoX, before deciding to build a dedicated race car. First, I used a C4 frame. Then just built a tube-frame... depends on how far you want to go...
Anton
Originally Posted by 1991Z07
I'm just getting ready to start this on my track car...using a flood totaled ZR-1 for the base of the build. I'm not going to strip it all down to bare frame...but I am going to get access to as much of the seam as I can by cutting away what I can, welding and then putting those pieces back in place.
Did you strengthen the front K-member as well as the front cross-member by welding all the seams? It appears that the pieces they used could get a lot of strength added by doing this. Admittedly, for the day, these cars were top of the heap but knowing what they did shows why the C5 and subsequent generations have a solid hydro-formed frame rail...
Once you start on a track-build you start to see a lot of things that they compromised on for production...areas where they got no significant gain for a street car and so they didn't deal with it.
Areas like the front shock towers...again, spot welded and small stich-welds done where it should have been solidly welded together along every seam.
GM was trying to get 1G on the skid pad with the 84 'vette. They did so in testing but never made it on a production vehicle. The 84 Z51 was as close to that as you could get and the suspension was so tough that the cars fall apart. Things like power window motors break up over time.
With that said... The C4 has a great frame, the C5 frame is newer and better. The C7 frame is even better.
If you go back to the development of the C5... they took the C4 frame and figured out the weak points. A dressed C5 frame vs a dressed C4 frame are not all that different. The torque tube was the main change and that was put in place to solve exactly the issues described above regarding the welding. They didn't go back to a prior frame or some totally new design. It was simply an evolution using the latest technology.
The basic principle is to weld whatever you can, weld where it is bent metal that is just spot-welded. Strengthen weak points with bracing. Buy some gassets and gasset the bends and joins where you can.
I built a stick model and tried to model the bracing.... It was a long time ago. I still have a C4 ZR-1, a 1992. I used it for AutoX, before deciding to build a dedicated race car. First, I used a C4 frame. Then just built a tube-frame... depends on how far you want to go...
Anton
I'm hoping to spank a lot of C7Z07's when I'm done...I'm using a carbon fiber hood, rear bumper and roof panel, Lexan rear window...and stuffing a 7.0 LS3 with a 2.3l supercharger on top. Shooting for 750 FWHP on E85. I have the cooling figured out...so it should last for an easy 20 minute session flat out.
Also putting C6ZR1 carbon ceramic brakes on to lighten even more. Can't wait until I get it done...Circuit of the America's awaits.
02-26-2014, 12:50 AM
