Body Flex Cure?

[laborisfree]

I know there are a couple of options to stiffen the body. But am unsure which is most effective and where the best place to buy is.

I am wondering about the system that basically attaches tubular steel cross bars to the underside and am wondering how much trouble that would be to have fabbed locally. i have access to a welding shop where labor is free. If I had plans or blueprints they could fab it for me.

 

[XS650]

Seems like it would make more sense to stiffen the frame. Any stiffners you attach to the body stand a good chance of starting cracks where you attach them.

 

[laborisfree]

ok, so any clues as to how to stiffen the frame?

 

[Hib Halverson]

This question has come up many times on the Vettenet, the CF, the CAC and other places....adding crossbars to the underside of a Coupe, like that on the 86-up convertibles, does little or nothing for stiffness but they do increase weight and decrease ground clearance. The crossbars on a convertible are there to improve that car's very poor stiffness just to the point that it approaches that of the C4 coupe. The coupe is already much stiffer than the convertible so the crossbars don't do anything in a practical sense.

Unfortunately, there is nothing you can do to increase the stiffness of an 84 appreciably, other than welding in a roll cage or at least a roll bar hoop with back braces.

You can make some very small improvements by 1) always keeping the roof in and tight, 2) making sure any bolt in part of the frame are always tight and 3) adding a "harness bar."

A problem with C4, even coupes and especially 84-86 coupes, is weak structure.

 

[laborisfree]

Will the Harness bar impair how far the seat will lay back. My 6'2" frame needs all the room it can get. I also assume that the T-Bar for the targa is a must for top off driving. A harness and a T Bar are reasonable suggestions. A roll bar may be over kill for my driving needs.

Thanks

 

[stumpy]

Have you tried a camber brace yet? I hear it makes a huge difference.

 

[rrubel]

Hib, to be honest my harness bar didn't do much to make the car stiffer... but I wonder why you don't believe RD Racing's Cross Frame won't help? It's like the convertible X-brace on steroids, but without much loss of clearance. It does add a bit of weight; if you're that concerned, though, lose the spare tire and throw a can of fix-a-flat in the back.

To Laborisfree, my RD Racing Cross Bar doesn't affect seat placement at all. However, if you add the harnesses themselves then the seat doesn't like going back quite as far on the tracks. It'll go if you force it, but with a power seat I don't like doing that.

[RICHR]

 

[Ken]

Will the Harness bar impair how far the seat will lay back. My 6'2" frame needs all the room it can get.

I'm 6' 1" and I had no problem with Dave's (R-D Racing) Harness Bar affecting seat travel. As a matter of fact, I just happen to have a harness bar that I got from Dave a few years ago (it's like new) for sale since I installed a roll bar now.

 

[John-C5]

I have RD Racings Cross Frame for my 94 coupe. I did a good job stiffing the car, I was actually surprised at what a different it made with the top on. It did enough to make the car drive well even with the top off. I presently have it off the car for two reasons, because of its design with the splice plates at the X and bolts from the bottom I figure I lost about 2” of ground clearance in the middle of the car. The second problem is that I’m having clearance problem between the frame and the exhaust bracket. I pulled it of after my last experience with a parking garage where I hit bottom really hard coming out of the garage on what didn’t look like a bad slope at all. I’m planning a little redesign to try and get back about 5/8” of my ground clearance and solve my exhaust problem.

 

[tntcorvette]

I have the R-D Racing Cross Bar and Camber Brace. Both a great way to stiffen up the chassy. You can jack up the car on 3 jackstands and remove/install the targa top!

I have a set of C4 beam plates (more for keeping the car in a straight line versus the rear kicking out on hard acceleration take off)

 

[Gary04Z06]

I have the Camber Brace and did have the Cross Bar from www.r-dracing.com Both really improve the way the car handles.
I recently got rid of the Cross Bar for their new S/T Frame Support (see sig) it help even more.:cool I recommend the Cross Bar and Camber Brace. I want to get the Cross Frame also, at some point.

 

[84c4]

I have RD Racings Cross Frame for my 94 coupe. I did a good job stiffing the car, I was actually surprised at what a different it made with the top on. It did enough to make the car drive well even with the top off. I presently have it off the car for two reasons, because of its design with the splice plates at the X and bolts from the bottom I figure I lost about 2” of ground clearance in the middle of the car. The second problem is that I’m having clearance problem between the frame and the exhaust bracket. I pulled it of after my last experience with a parking garage where I hit bottom really hard coming out of the garage on what didn’t look like a bad slope at all. I’m planning a little redesign to try and get back about 5/8” of my ground clearance and solve my exhaust problem.

John,

I sent you an email on your problem, give me a call sometime.

Thanks,
Dave Cooper
R-D Racing Enterprises, Inc.
573-756-6954 Office
573-756-6372 Shop

 

[84c4]

Hib,

You should really try driving a C4 coupe with a "Cross-frame" installed sometime before you post an opinion on what they do. I guarantee you that you will "Feel the difference". Our Customers will tell you that the weight gain is well worth it.

Thanks,
Dave Cooper
573-756-6954 Office
573-756-6372 shop
R-D Racing Enterprises, Inc.

PS - We have a Camber-brace that will fit your ZR-1 now, if your interested, they'll be on sale for Xmas.

 

[tntcorvette]

I have the Camber Brace and did have the Cross Bar from www.r-dracing.com Both really improve the way the car handles.
I recently got rid of the Cross Bar for their new S/T Frame Support (see sig) it help even more.:cool I recommend the Cross Bar and Camber Brace. I want to get the Cross Frame also, at some point.

How much does that impair rear view vision out of the rear view mirror???

Also, how much does it weigh versus the cross bar & how much?

 

[Gary04Z06]

How much does that impair rear view vision out of the rear view mirror???

Also, how much does it weigh versus the cross bar & how much?

Rear vision is blocked, some. Once I got use to it, which didn't take long, it was fine. If a car is behind me, I can see the grill area, but can't see the driver. So I can tell a car is there, that's all ya need to do anyway. Weight is around 45 pounds I think, Dave, is that right??

Mine is bolted in, but they can be welded in.
Call or e-mail Dave for the price, he had a sale going on but I don't know when it ended. I reall like the S/T!!

 

[tntcorvette]

can you let the seat back all the way?

 

[Gary04Z06]

can you let the seat back all the way?

The driver seat goes all the way back. The passenger is restricted a little, but it hasn't bothered any one yet, still plenty of room.

 

[Hib Halverson]

Hib,

You should really try driving a C4 coupe with a "Cross-frame" installed sometime before you post an opinion on what they do. I guarantee you that you will "Feel the difference". Our Customers will tell you that the weight gain is well worth it.

Thanks,
Dave Cooper
573-756-6954 Office
573-756-6372 shop
R-D Racing Enterprises, Inc.

B]

First, I did not express an opinion. I stated a fact and I stand by my statement. It is based on information GM provided me some years ago about the C4 Coupe structure when fitted with the production convertible, underchassis, X-braces. GM tested that configuration and decided there was no practical improvement.

Second, I'd be glad to test a coupe with these braces and offer a subjective opinion, if a car with them is available in southern Californa. Such a test must include 1) driving the car without braces then 2) adding the braces and driving the car again over the same route of my choosing.

Now, if the cross-bars RD Racing or other aftermarket entity builds are different than the production convertible braces, and, in theory, do increase a C4 coupe's stiffness in torsion and bending, I ask those who manufacture such products to post some data to support that. With all due respect, just anecdotal accounts of customers "feeling the difference" (whether guaranteed or not) does not support the theory. To be honest, I question the ability of many laypeople to be able to feel a small change in a vehicle's stiffness. For the average driver to truly feel a change in stiffness, the contribution of the x-braces to a coupe's rigidity often needs to be significant and...for me to believe the contribution of such aftermarket braces is "significant" I'd need to see some test data.

That said, I will admit, if users of crossbraces are making such comments about the product installed on a coupe with the roof out, then, I'll agree, crossbraces probably have a positive effect that will be noticeable in most any subjective test.

Elsewhere in this thead the statement was made that the addition of these braces costs 2-in. in ground clearance. I know that if I installed such braces on my C4 (which has been modestly lowered), the loss of 2-in of clearance would have me unable to drive the car over some obstacles one finds in normal driving such as medium-to-high speed bumps, certain manhole covers and some driveways. In addtion, it's unlikely these crossbars, if they occupy the same or greater volume of space as do the production, 86-96 convertible x-bars, will clear my exhaust. Lastly, my guess is that anyone who's lowered their coupe for racing would have more of a problem with a 2-in. loss in ground clearance.

That said, virtually all later C4 base coupes (this incl. ZR-1s) which had unusually high ride heights (compared to, say, cars built prior to 92) would have little or no ground clearance problem with crossbars no matter if they were production GM or aftermarket.

PS - We have a Camber-brace that will fit your ZR-1 now, if your interested, they'll be on sale for Xmas.

What is the projected price of this product. Also, what's the price of the crossbraces for a coupe?

 

[84c4]

What is the projected price of this product. Also, what's the price of the crossbraces for a coupe?

Both units are on sale for Xmas, please refer to the following thread; http://www.corvetteactioncenter.com/forums/showthread.php?s=&threadid=40293

The true ground clearance reduction for the Cross-frame is 1.43" where the frame crosses over and 1" under the floor pans. I have my 96 setting on the ground and yes I do drag it once in awhile, but the frame was designed to to handle the abuse of an occasional kiss from below.

Dave

 

[Hib Halverson]

Ok....I understand that the LT5 camber brace is 205 bucks.

C4 Cross-frame = $320.00 + $27.50frt
C4/C5 S/T Frame Support = $476.00 + $47.50frt

I take it the cross braces for the Coupe are 320 bucks plus 27.50 for shipping. Is that right?

What is a C4/C5 S/T Frame Support?

I also understand the actual change in ground clearance to be about 1.5-in. rather than 2.0-in. Have I got all this right?

Lastly, is there any place on the web where images show these crossbraces installed under a C4 coupe?