That is quite an impressive build you have. I like the way you have used your lift to anchor the chassis and measured the torsional strength.

A ladder chassis is by definition a two-dimensional structure and just adding crossmembers does not make it stiffer. (that is not completely true, but you will mostly add weight and a little increased stiffness).

You have made some very interesting modifications, i will certainly take this into account when i ever remove the body.

There was a member on here that did quite a bit of "two dimensional" frame stiffening. I forget his username but he experimented with the structural foam filling. I looked into it and the one drawback is that you better be 100% done modifying your frame before you foam fill it because you can no longer weld on foam filled areas. Im waiting to figure out how to add another pickup point for my cage (among other things) before I dive into the foam filling. Seems like a very good lb per flex reduction option.

Well, for my purposes I believe it was worth it. I like to do a lot of track days with my car, and that involves tweaking the suspension geometries and spring/bar rates to get these antiques to handle decently at speed. Any improvement in the frame stiffness reduces the "fuzziness" of the suspension changes.
For a purely street usage vehicle I think the main benefit to a stiffer frame is a slight reduction in the squeak factor when driving over uneven pavement.
Fully welding the frame will increase the rigidity, although modestly, and it's an easy thing to do when the body is off. A couple days of grinding and welding will yield a slightly more pleasant personality to the car in everyday driving.

I would think that a 4 pt cage would solve most of the problems.
That is on my list.

R

I have a Sharbar on my vert and yes it helps immensely, felt like a different car 1st time I drove it after the install. I also have 550 lb front springs, a VBP 360 rear fb spring with Bilsteins front and rear. The one drawback to the SB is that is restricts access to the rear hatch somewhat due to the lower bar, but if I need to put something larger back there I just open the rear deck. Just remember that this is not a true roll cage while it does add rigidity, ease the installation of a 5 pt harness and looks nice it can not be thought of as a substitute for a true roll cage to use at the track.

Thanks for the feedback! That's what I thought. Do you have a front spreader bar as well between the front shock towers? I was shocked how much the Speeddirect,com bar helped my 78-with the stock OEM mechanical fan, not electric fans! I would imagine that a Sharkbar and a front spreader bar would be the ideal setup outside of a full roll cage/bar which is not practical on the street.

Don't have the spreader bar but am seriously considering buying one from S Direct. Shipping up to Canada is rediculous if they do not go through USPS as the couriers hit us with all sorts of addl'n fees. At least Corvette Central from time to time has free shipping and no addl'n border fees.

:iagree:

What a difference in ride comfort....before avoided all roads that were not smooth, avoided driving over R.R. tracks, it was just brutal...

In a post above, I mentioned the stiffening that "Dirty Rat" did to his 69 frame. I found a photo that he sent a while back and it's in "My Corvette Photos". The bracing is slightly different at the rear than I remembered.

So don't tie in birdcage?
 

Lots of good info here. I built a backbone frame in mine and then tied that to my kick ups to give it a 3 dimensional component. I cut up my floors, etc. I am at the point where I could weld the birdcage down to the frame but am apprehensive since I don't want to create any body issues. My frame is heavier but it's a street car so it is a trade off I was willing make. Also, all the weight is very low in the car CG is good.
I think vertical tie in to the birdcage could add a real torsional benefit to the chassis.
Has anyone ever tied them together? Results??
Thanks

That sure does sound like you have to post some pictures....:thumbs:

I am very interested in your solution. When the body of my '80 comes off i want to make the frame as rigid as possible without adding hundreds of pounds of steel, so i have to find the "sweet spots" where adding steel is the most effective.

Any pics of your progress would be greatly appreciated!

Thanks

Please post some pictures. :thumbs:

A backbone setup has always been my prime interest in stiffening a C3 frame. It puts the additional torsion strength/material right in the plane that the frame twists in. If it weren't for possible cutting and modifying of the tunnel shape to clear the backbone structure I would have done that to mine several years ago.

how much stability is a fiberglass body going to give you?

On the 70 to 75 Verts, having the door hinges tight with good bushings and pins and the door guides adjusted correctly and fitting snug will help tie the front and rear of the body. Good guides and latches adjusted correctly on the deck will help too.

I was thinking that if a person used aluminum body mounts along with a 4 point roll bar that attached to the frame and also to the soft top mounts at the sides, it would really tie the car together, short of using a 6 point roll cage. I just really don't want a full roll cage in my Vert for mostly street purposes.

I have solid motor mounts with a BTO cross-member I will use a poly tranny mount on. Probably will mount my differential solid by removing the bushings in the cross-member and welding disks in their place with a solid front mount. It will raise the diff approximately 3/4" lowering CG and raising the roll point. It should really tie the rear together and make that a lot stiffer.

I have a spreader bar and tubular upper A-arms that I am going to lower the frame mount position to raise the roll point on the front.

All this combined with welding the frame and adding a lot of gusseting should really tighten the car up. I'm not really concerned about vibration and noise form everything being mounted solid. With the top down and the pipes roaring, who's going to notice?

I also have Steeroides rack and pinion, hydroboost and 18" modern performance tires. This thing was loose as a goose when I got it. I can't wait to finish it and go for my first ride!:woohoo:

Now if my back would heal up, the weather would warm up, and work and life would get out of the way, I could get going on it!:(

First pic post
 

This is the concept. I will post pics soon. But the basic idea is to use stringers fore to aft and the tie it over the drivetrain but under the floor to the main crossmember. Then continue the top portion on back to the next crossmember. I then triangulated back to the main crossmember and stringers.
You can utilize the space behind the rear firewall panel to tie in the frame or body as you desire and keep it under the skin. Just remember I cut up the floor since there is no way I know of to do the backbone unless you are willing to cut it. I am not done yet but have a good start. I took square tubing and made a framework over the transmission and made it fit around a T56. This is welded to the stringers. I boxed it under the center console to tie it together. I plan on using a bolt in crossmember under the transmission to tie it together more effectively. I lowered the floor because I didn't like how I sat so that gave me more options on seats but created more challenges. So I don't pretend to be a great fabricator or have the tools it requires to be one. I am still trying to figure this set up out. So when you see my pics remember its a work in process....

Great explanation, i am now even more interested in the photo's. You are thinking in the same direction as i am. Only problem is i still haven't figured out a way to strengthen the front end. Your sketch show a great improvement in the rear but is leaning back to a 2-dimensional (flat) front side. Very little room to work there. Have you thought about a structure under the dash connected to the transmission tunnel reinforcement and under the hood to the front?

Keep up the good work!

A friend of mine who worked with plastic manufacturing for years, retired now, said he would fill the frame with structural plastic. Said it would make the frame several times stiffer without much extra weight. I had actually heard of this before, but what I read about was different than what he was talking about. I'll have to ask him about it again. You would still want to weld and gusset the frame though.

Chevy Power Book
 

Here is a copy of the Chevy Power Book

That's very similar to what I wanted to do if I could have fit it in the original tunnel. :thumbs:

Some pics
 

Here is my interpretation of the drawing, I added more to the front as I agreed the drawing was lacking up there too. I have decided to tie it all together if for no other reason but to seal up my lowered floors. I am also bonding 3/4" plywood on the floors of each side. I am also tying the center hump to the birdcage and frame to tie it all together. Front and back. But I don't recommend the major surgery I have done. It just keeps snow balling....... It may be years before she is on the road. It is overwhelming sometimes.... It may be a while before I can tell you if it is as stiff as I surmise. I don't have a way to anchor it and do proper testing like others have done here.
Thanks for your support. I am open to new ideas and willing to try them out- hey, it keeps me out of the house....