Tom400CFI

It is real. Here are some excerpts from "Corvette from the Inside" -by Ddave McLellan himself, and also from "The Newest Corvette From A Through Z51" by Michael Lamm. both fantastic books...








The C6 (C5, really, the C6 is really a new body on a C5 platform), is the platform that Dave probably wanted for the C4. Dave and his crew explored a central tunnel and a torque tube design in the C4, but those features didn't make it to production. IMO, they ran out of time and money and had to make concessions by using the C-beam and the SMC floor panel forward of the seat mounts.

You are right that a fully boxed tunnel adds a ton of torsional rigidity to the structure, and that is exactly what the C5^ uses; a boxed, plated on the bottom, tunnel.




The C-beam is way lighter than the steel that would be required to do the same job. C-beam weighs about 8 lbs. And the trans cross member would consume space. That is why C5^ still use a tq tube rather than cross members.

ddahlgren

My ought was to put cross members inside the boxed section so maybe 8" long and could be aluminum as well.

Tom400CFI

Was messing around w/the 'Vette Kart on jack stands and discovered this amount of flex. Watch the rear halo vs. the w/s frame. I'm simply pulling up and pushing down on the right rear corner of the frame, while it's jack stand'ed under the frame about even w/the rear of the engine, and on the left rear frame jack point. I was disappointed to see this, to say the least.



This one, I set the camera ON the rear halo so you can see it's movement relative to the front of car.

frankinvett84

Wow!

drcook

I read this thread before and after I purchased my car in July 2016. (this thread was started by Tom in July 2010).

Paying attention to what everyone said, I acquired a harness bar that attaches at the upper seat belt bolts and at the targa top holders. Supposedly the screws should have been long enough to put the top holder back, but they aren't in my car. Since I don't take the top off, it is no biggie for me.

I also acquired a camber brace. It is on the car also. There is a X-brace from a convertible in the shed, this summer I will have it boxed and then install it.

I/we (my wife) could immediately tell the difference in the car after installing the harness brace/camber brace. Keep in mind our car is not a high mileage machine that has been rode hard. It was a 11,800 mile car that truly was owned by a little old lady. I have her paper work from purchasing the car.

The car now has 17,000 on it. Even a low mileage, babied C4 has squeaks and moans. A lot of these, well most, went away when I installed the braces. The car feels LOTS better.

Once I put the X-brace under the car, I am positive it will be even better.

The trade off was the extra weight.

MrVette90l98mt

Wow!

can somebody with fame stiffeners of any kind do the same test please! I am interested in the longitudinal tension rods that pre-stress the frame rails and see if there is any gain in rigidity. I want to drive topless without my car being a wet noodle!

bill mcdonald

Is it possible to do the test with the top installed?
Or is that not possible?

drcook

All that movement is why these cars are stiffer with the top installed or one of the targa bar setups that Tom G. sells here in Ohio. It is also why putting in the harness bar tied the sides of the car together and helped out.

Tom400CFI

That's true. Car would be way, WAY stiffer w/the top on.



I could. The top for this car was broken when I got it. I threw it away. I could re-install the top mounts and put my '92's top on to re-test. I'm confident that the flex with the top on will be imperceptible, though.


It's obvious that when you remove the top, car flexes more. And it's obvious why. But seeing how MUCH it was, just by the force imparted by my hand...yikes, I said to myself.



.

bill mcdonald

I know it will be stiffer, but with this opportunity to see it in a stripped down car would be pretty cool to know what is what.

Been looking at how other cars are built and some ideas were forming in my mind.

pologreen1

Very valuable info for sure.

Are you considering stiffening it? I assume roll cage and stuff over the common stuff at this point right?

I'm just thinking what a perfect time for these people selling parts to give you a little incentive to install and show what their products do.

Tom400CFI

I know it! Hey....I'm totally keen on taking samples to test!

I'm going to chop the halo off, and the w/s frame, then cage the whole thing...that will stiffen it dramatically.



O.K. I'll see what I can do about putting a roof back on it for another test.

MatthewMiller

It just confirms what I perceive when I take the top off my car. Of course, I have much higher spring rates (1125f/550r) and damper rates than stock, which just makes it worse with the top off. But it's just stunning how flexible these cars are with the top off.

GREGGPENN

One also has to ask (OK me!!! LOL) how much rigidity the body panels add? I am surprised to see this thread resurface. But hope it leads to more thorough conclusions. I, myself, have been convinced [enough] about the benefits of frame strengthening that I installed a camber brace several years ago AND bought an x-brace (though I had to abandon it due to side-pipe undercarriage interference).

One of these days, I might redo my exhaust and revisit frame stiffening approaches. Thanks for keeping this issue on the burner guys!!!

GREGGPENN

Oh yeah....can't wait to see feedback from all the guys saying x-bracing and vette-2-vette bracing is useless.

Tom400CFI

Very little. Basically, none that is meaningful. There just isn't any strength in the SMC or FRP sheets. And anyway, the flex is mostly between the A-pillars and the B-pillars....only panels there are the rocker pieces, the doors, and the roof. The rocker panels don't do anything but cover the frame rail. Roof, does a lot as we know. Removing it reveals the weakness that my vid illustrates. Doors? They might add a little stiffness when closed, but that isn't their job.

Skidmark1

Skidmark1

<div style="text-align:left;">Soooooo.......<br />vette 2 vette bracing cable tension good or bad?<br /><br />skiddy</div>

TorchTarga94

Neither really. I had them on my car for a few months. Noticeable? Yes. Worth $400 for minimal improvement with top off? No.

I decided to put my car on a small weight loss plan so I sold them off.

pologreen1

I can say for sure I would rather have an old R&D x frame brace than the stock gm brace on my vert even though I use the hard top anyways.

I can't wrap my head around the turnbuckle deal preventing twisting or flexing like shown in the video.

I think the R&D X brace would be incredibly effective if you are willing to modify your car or change the center mounting. IMO the center is the weak spot of the X brace. It is bolted to the car, but barely.