69427

I started to do the torsion math numbers, but then I noticed there's no arm length mentioned (just force and degrees). I assume it to be the Newton force at one meter, so I ran some numbers and got 2768 lb-ft/degree, using the original number of 214kN/rad.

Please correct me if I misunderstood something in the postings.

Tom400CFI

I don't know how much work it would be, but is it reasonable to ask you to hollow out the rocker rails and the put in a trans tunnel, and floor boards...and see how it specs out for torsion? My idea is that if your hollowed out model is AT ALL reasonable in the calculated specs, then we could start adding on things and see what happens. But again...I don't know what's involved in that model building. I don't know what I'm asking. :o

StealthLT4

Imagine if you held the rear two suspension mounting points stationary, and put the front of the car in a "jig" that supported the weight (did not allow vertical or horizontal motion), but allowed it to rotate around the car's forward axis (the axis going from the rear to the front). Then you push with 214 kN of force on one of the front suspension mounting points straight up or down, and the car would rotate one radian (57*). Obviously it would snap before it got this far, but you get the picture.

I just crunched the numbers for lb-ft per degree of rotation, and I apologize for my earlier post. It doesn't have anything to do with the wheelbase, I meant the track of the car. Here goes...

kN per radian of rotation: 214
degrees per radian: 57.29578
kN per degree rotation: 3.735005
lbf per degree rotation: 839.6625
front track (in): 57.7
front track (ft): 4.808333
front moment arm (ft): 2.404167 (=track/2)
torque per degree rotation: 2018.689 ft-lbs

Someone correct this if I'm wrong. Seems very far out of line with the posted C3 specs, but then again the C3 is basically the C2 chassis, so pretty old...

corvetteronw

This is not the technical answer you are looking for. Only my seat of the pants experience. I installed the Vette2Vette torsion bars a few days ago and tourqued them down good and tight. I did a test run on a local twisty 2-lane blacktop road that has about 8 of the "30mph" curves (per the peed limit signs)> I have run this road several times with my previously owned 60,000 mile stock suspension 87 vert that has the standard X brace along with a GM hardtop that I modified to fit.
I also ran this with a 40,000 mi LT4 vert with no hardtop and F45 selective handling turned to the max setting.
I ran this road 2 days ago with my 110,000 91 coupe with the targa top off. It has the FX3 selective ride option and I had the switch turned to the max setting.
My impression was that the 91 took the curves faster than the 94 which took them faster than the 87. With the torque of the L98 engines at the speed I was running the LT4 did not really make a difference. Handling did. The tires were new on the 91 and 87 but were not high performance skins. The tires on the LT4 nice, meaty GS D3s with only about 5,000 miles on them.
I drove the 91 over a set of double railroad tracks that I must negotiate on my way to and from work daily. I was suprised that the 91 did not rattle over these tracks like it used to do. It feels tight and drives like a much newer car. I love these rods!
It took me under an hour to install these. There are brackets that use 4 bolts to attach to the front X brace threaded holes that are drilled on all 86-96 coupes and convertibles. The rear brackets use the bolt that attaches the lower dog bone.
Here are some pics. The car was only about 18" off the floor so I had a hard time getting good shots.
The kit:


Front bracket in place:

Rear bracket in place:

Installed (pic is not the best):

Here is a pic of the pre production model on a ZR1 I look during Bloomington Gold:

It appears that the low point of the installation is at the rear brackets. I measured with the car on jack stands and the distance at the rear bracket is the same distance to the floor as the front portion of the Y pipe. Since my rear Y pipe has no scrapes on it I assume that it never has dragged on anything. I do have 18" C5 wheels on the back now so it may sit a little higher than the stock 17" wheels do.

Disclaimer: I do not receive any commission on any of these that or sold and I am not an employee of the manufacturer. Jeff over at the Corvette Guru forum is putting together a group purchase. He is the owner of the ZR1 in the picture.
I just want to say that this 110,000 mile coupe drives tight and like a new car even with the hatch roof off.

Charleston2012

So, do you think the R-D racing S/T frame or the DRM Chassis bar help stiffen the chassis?

Tom400CFI

^I don't know what either of those things are^. Can you post a link or two? EDIT: I see. They look like this:


That may help a little...but I can't see it helping anything forward of the back of the seat. IMO, the real problems start at the back of the seat and go forward. The rocker/floorpan is terrible, proven by what happens when you remove the roof.



I had forgotten about the lever arm length. I don't believe that was clarified anywhere. You assume 1 meter (not a bad assumption)...StealthLT4 thinks the arm is at the lower ball joint...I don't know. Anyone else have an idea?

Charleston2012

No pics on their site anymore, but it is a 4 point type roll bar.
http://dougrippie.com/?p=930
R/D racing st frame second to bottom of this page
http://www.r-dracing.com/stframe1.htm

GKK

If these rods were to be stitch welded (with small strips of plate steel every 8" or so) to the pinched seams, they would really tie the front and rear high strength steel frame sections together creating a very strong "perimeter frame".

mnstrlt1

here is a thread that I started about developing a "real" chassis stiffening brace.

http://forums.corvetteforum.com/c4-t...of-the-c4.html

I'd still like to see something similiar to this for a c4....

Aurora40

It's just a unit. If the thing had 57,000 lbs-ft/Rad, it's the same as 1,000 lbs-ft/deg. There is no need to twist the thing a full radian (or full degree for that matter) in order to use that as the units.

Edit: Stealth beat me to it:

pologreen1

The people who say not so much, are usually the ones that don't have them, because they can't see, or understand in their own mind why it might work.

Any, and all bracing I have put on my own car has made improvements, and or changes in handling, but mostly rigidity.

I have a vert, but if I get the chance at a R&D X frame brace I am putting that on just to see the difference. It looks a lot more sturdy than the stock one. The stock one is flimsy when not attached at all points.

I am expecting bigger changes when I put my 8 point roll bar in.

69427

I don't have to imagine doing a frame torsion test. I actually did it. (Apparently you skipped over a few posts.)

I believe you've mistaken me for someone else.

Regarding your calculations, I have to disagree. We're only discussing frames here. Track width does not enter into the picture. We are twisting the frame at the wheelbase points, as this is where the forces are inputted into the structure. Additionally, it would make no sense that the rating would be 214kN/radian and at some moment arm other than one meter. That's why I posted the 2700 ft-lbf/degree calculation. I'm looking for feedback on why these numbers may be inaccurate, given the torsion info on the first page.

littlesk8cracker

anyone got a pic like that for a convertible?

88BlackZ-51

Tom.

Maybe speak to some serious road racers who race or used to race a C4 (roadracing). Most of these guys have probably moved up to a C6......

Tom400CFI

Road racers use cages, which I don't want. I already had a C6 and didn't like it. I moved the other direction; "down" (?) I guess you'd call it. I'm happier for it though so...




I don't. Chop the hoop and put ins a Cross car brace and you're probably pretty close to a 'Vert.

Trog

Appears the front brackets would interfere with a stock or RD Xbrace. Can you comment on that?

I have a stock X on my coupe. I welded plates into the rear pockets to give me enough thickness to drill holes & tap them. I also boxed a good part of the stock stamped X itself. Anyone who has one will know they are a stamped into a modified W shape & it was easy enough to lay a strip of sheet metal along the bottom of the W shape & weld it in. The resulting tube/box really made it stronger. I also obtained the bolt/straps that lay/go through the floorboards & added another strip of sheet metal strip between it & the two inner seat mounting bolts to help tie it all together.

Midnight 85

With the exception of the plates in the rear pockets I did the same thing to the x-brace on my coupe. I was very happy with the results, much better handling over the regular x-brace. Between the boxed x-brace and the camber brace I can't ask for better without adding intrusive stiffeners.

howdo

You wouldn't happen to have pictures of how you did this, would you? I am interested in stiffening my '91 coupe, and this sounds like a great approach. I also like the rods that vette2vette sells, but they are out of my price range ($700). I figure I could get the stock x from a salvage yard, and con a buddy into doing the welding.

Trog

will post some this evening w/ I get home. I just made cardboard templates to fit the pockets in the back, cut out the steel (1/8" thick), grind till it fit in the pocket. Then mig welded around the edge. Bought the alum spacers that go in the rear from local stealer... cut them in half (thickness as my steel buildup takes space) Used holes in rear of X brace with alum spaces to mark holes to drill in some 1/4" thick by 1.5" wide steel strap. Drilled straps to size on metric tap to match front bolts. Used front bolts & small jacks to temp install X brace, this held the straps in place. Welded straps onto steel in pockets I had welded in earlier. Drilled holes the rest of the way through the steel plates. Tap holes for bolts. 4 corners are now ready to go.

Took me awhile to track down the straps that go through the floor boards... They & the X brace came from a vette wrecking yard... remove seats, remove carpet. Drill holes in floor from the bottom through existing holes in the X-brace. When I put the straps w/ the studs through the holes in the floorboards from the top I felt there wasn't much there that I was bolting too. Residue on the straps indicated they had been expoxied into place on the car they came out of. The floorboards are pretty much the same material as body panels. So, I took some sheet metal strips about 3" wide & that was able to hit the inner seat mounting studs & I think one of the bolt/studs now going down through the floor into the X.

Anyone who welds or a competent welding shop should be able to box your X brace itself.

Shape is a bit like this, end view if cut: |-|_|-| The top horizontal part of course doesn't sit down like that, but best you can do w/ the keyboard. I welded a strip along the entire top/middle... so now like this |-|=|-| imagine the = sign being further (up & down) apart of course.

I also put a wider plate along then entire bottom along the front half of each arm of the X only, as I tend to scrape them over things more often. Just to give it a skid plate but that also boxed in the outer two channels as well. All told, the front halves of my X brace are 3 tubes now & really tightened things up. Although just having the X in the first place helped on its own. But like everyone else here, I wanted more. I didn't use as heavy of metal as the X itself, that would have been more weight & prob. overkill. I ground the welds down to look nicer & then painted the whole thing. Oh, I used some welding paint on the inside side of the metal making the box before welding in to help against corrosion.

Going to try something else here w/ keyboard

|--| |--|
| |_| | before

|--|--|--|
| |__| | after part 1: upper middle welded in

|--|--|--|
|__|__|__| after part 2: now welded in bottoms as well w/ 1 full width piece.

dclafleur

A lot is over my head, but I'm willing to listen and learn!