MZee

My only questions is? Does the ride change to so stiff it rattles your teeth, or you feel no body flex and it's an improvement from creeking?My roof creeks ,
MZee

Greg Gore

The roof is triangulating the frame and as rocco suggested probably contributes more to stiffness which engineers measure in Hz than any other thing you can do. Chevrolet called the new unitized C4 construction design a Uniframe but it might be more correct to describe it as a Unitized Body when the roof is in place and a Uniframe when the roof is not installed. The engineers had a tough job in achieving adequate frame stiffness without the roof. The myriad of small things GM engineering tried during development probably picked up a Hertz here and half a Hertz there and McLellan looking at the big picture had to decide what made the cut and what did not.

I can understand not everyone will respect Gordon Killebrew but he is still an engineer with credentials and was on the engineering team and he was there when the various engineering proposals were mocked up and tested.


The C4 made history as the first unit-construction Corvette, using this sturdy "birdcage" or "uniframe" structure.

jemidyette

Great info there. If you have ever met and talked to Gordon personally, you would know his genius. I actually purchased the stiffening bars from him in person and was able to talk to him and his sweet wife for quite a while. Gordon told me that the original design of the C4 utilized a T-bar roof like the F bodies, but switched to a targa top last minute, causing basically a time deficit to engineer a stiffer frame. The X bar on the convertibles helped a lot, but that wasn't even introduced until a couple years later.

These stiffen the frame, not the suspension. It just eliminates body flex.

LT5corsa

I installed this on my ZR-1 (80k mile & climbing) 2 weeks ago and what a substantial difference

I've had the pleasure of knowing Gordon for years and was very interested in buying this, but just couldn't pull the trigger

I did, installed it and couldn't be happier!!! (Thanks to Ed for his help!!!)

Highly recommend this product. Thanks Gordon for making this!



David

Tom400CFI

I still have a hard time believing that these work. But, they are receiving pretty universal praise from those who have installed, so...

What REALLY concerns me is longevity; I suspect that they work by preloading the spot-welds in that part of the frame. If so, what does years of bumps/impacts do to the frame? Maybe nothing...IDK.

mxw128

Hey David: have you tried a top off ride yet?? I'm curious if they help with the cowl shake and overall wet noodle feel without the targa...

GREGGPENN

Hey Tom, I decided to bump this thread after re-reading a few on this product. I got tired of waiting for the RPP_Corvette x-brace and found an R&D x-brace last spring. I bought it but it wouldn't work on my car. Too much going on in the mid-section with Vette-Tech headers and pre-cats. (I'm saying the x-brace contacted these components and would have required significant reconfiguration of my exhaust).

So, I sold my x-brace and have reconsidered this V2V frame stiffener. With a rehabbed suspension and this brace, I would hope to get a much tighter feel over road imperfections. But, being the question-asker I am, I emailed V2V to get more feedback. I asked Jason specific questions about the design and longevity. I asked why GM picked the x-brace -- if it wasn't "better". (I also asked if he knew whether it would clear my SideEffects system).

I suggested if they'd take some time with their reply, I'd post it here since there have been many posts questioning the efficacy of the design as well as the longevity.

Here is Jason's reply:
The basic theory behind the stiffening system designed by Gordon Killebrew is that it puts the frame rails in compression and does not allow them to flex under load. Putting the frame rails in compression can be accomplished by using a piece of cable instead of a bar system, if desired, but will not have the same effect. A cable will only prevent the frame from flexing in one direction, up under load, whereas the stiffening bar prevents the frame from flexing both up and down under load. The stiffing bar does not become a structural member, like the frame rail, but is a stabilizing or stiffing member, that works as a unit keeping the whole frame system stiffer by not allowing it to flex under load.

A good example of this is a pre-stressed concrete beam. Concrete has very little strength in tension, but has extreme strength in compression. The way that concrete beams for bridges are constructed is that a form is built and cables are put inside the form and pulled tight so that when concrete is poured into the form and cured, it is under compression when the form is removed. If the cables were not there the beams would be in tension and would not be able to support their own weight across the span.

The X-brace accomplishes a similar effect by bracing one frame rail against the other. This method distributes the load between the two rails and adds quite a bit of rigidity to the rail system, but it has one major drawback. It blocks all access the underside of the drive train, if you want to remove the transmission the X-brace must be removed first. I don’t know the full details that went into GMs decision to use an X-brace for stiffening the frame system for the convertibles, but I would guess that it was cost. It is much cheaper to stamp out a piece of steel than to fabricate brackets, and add all the other components required for the Gordon Killebrew solution. Plus GM would have had to pay him close to $100k for his idea. The X-brace apparently did not function properly for the Corvettes that were raced because they turned to Gordon's System for the solution to the frame flex problem on the Tommy Morrison challenge car and had extremely good results with it. We have had customers with convertibles order our system to replace their x braces. They have called with nothing but good feedback in the difference between the two.

Regarding the durability of the system, we have used the basic design, that Gordon designed for racing and have made a few modifications to move the bars further away from the body, but retain the same stiffening affect. This type of bar and bracket system has been used in racing and aftermarket modifications for many years. The rod ends are rated, by the manufacturer, as being capable of a load of 11532 pounds each, it is unlikely that normal street use will ever exceed that load.

We guarantee that you will like our product, If not we will refund your money. We have had only one request to return a set and that happened after someone ordered them and totaled his Corvette before the bars could be installed.


Jason

bolowbc

Hey GREGGPENN, I'm a long time member and have seen your posts here and there, so I thought I'd chime in.

I had my Vette out for several months to get some work done. I had a convertible x-brace to put in, because I wanted better ground clearance instead of the R&D.

Welp, due to LT headers, the shop couldn't get the convertible x-brace to work either. The shop had said they just installed the V2V system on another customer's vette and the difference was night and day... the caveat being that they had fabricated brackets for the kit and welded it in, instead of just bolting it in, for which the kit provides.

There was a pretty big difference when I got my vette back, much less plastic squeaking or rattling when going over bumps. The only problem is, I had an AZ speed & marine bar installed at the same time (similar to the R&D crossbar). So I wish they were installed sequentially so I could see how much of the change is due to either one. I already had the R&D brace that goes up front.

I've reading all the posts about this topic for our C4's, and this particular product as well. I also found it hard to believe that two simple bars could provide any sort of difference. However in one of the threads, I had posted a picture I found of a cross section of the body, and you can see the longitudinal beams at the door sill are actually hollow.

I think if you get them installed by welding them in, you won't be disappointed. I'm assuming you would notice a difference without welding too, and if there's a money back guarantee, I'd say you might want to give it a shot if you are on the fence. I'm pretty happy with the results.

JoeUser

Semi-old thread, I know. But, I'm definitely interested in these.

Someone asked earlier if these could be used in a vert (either with or without the cross brace), but I didn't see an informed response.

I'd love to get rid of the cross brace in my '96 vert, mainly for exhaust clearance and for easier access to the underside components. If these braces would allow so I will order them today.

If not, then has anyone installed these in combination with the cross brace in a vert? Pros or cons?

Tom400CFI

They will work if you remove the X-brace. They bolt to the same locations as the X-brace does.

JoeUser

Thanks for the response. I think I'm going to order a set.

QCVette

Thanks for bringing this thread back.

I have been reading about these for a while and I am on the fence about trying them.

To me it seems like adding the brace parallel to the frame rails wouldn't do much. However if it does, it says that the frame rails must be flexing/bowing up and down. I would have thought that the frame rails were pretty strong.

As much as I am a skeptic about how it works, I also see only positive reports from people using them.

I have been reading all the things I can find about them, but haven't brought myself to the point of spending $500 yet.

Tom400CFI

I think the frame rails are rigid in theory due to their large cross section, but not in practice due to the fact that they're many pieces, marginally spot welded together. I'd bet that if the same frame rails were 1 piece hydroformed, the car would be a good bit stiffer.

I read/heard that Challenge Cars had the lips ground off or folded over and a continuous bead welded on all seams, and that "helped a lot".

Also, in one of the Corvette books, Dave Mclellan makes a comment about a "hinge point" in the frame, where the rocker rail meets the front section rail. IDK exactly what that means, but I wish I could understand that better.

The Frame stiffeners in this thread attach rear of the rocker rails to what I would call the "rear bulk head" and in the front, ahead of the rocker rails, under the door posts. I THINK this device works by compressing, or loading all the spot welds in the rocker rails, their connecting points, and making the piece behave like a stiffer piece.

LT5corsa

I was probably more skeptical than you were... The convertible X brace makes "more sense" and didn't understand how the no flex could work!?!?!?!

Bonus is, the no flex doesn't take away from the ride height like the convertible X brace does and that's why I never installed the convertible x brace

If you drive your car, you will love this modification!!!



David

DrDyno

JoeUser

Just ordered a set. I'm hoping that they're a functional replacement for the cross brace, which will make it easier to get to underside components as well as stop the exhaust pipes from contacting the cross brace.

Edit: Just got off the phone with V2V, and the kit is shipping today. Since we're going to have semi-nice weather the rest of the week, I'll likely get these installed on Thursday or Friday

Another Edit: I received these about a week ago, just haven't gotten around to installing them yet (too many things going on, and waiting for a little warmer day). The instructions supplied leave little to be desired (B&W photos, and not enough of them, frankly). The front braces are a simple matter, but it took me a few minutes to mentally picture how the rear brackets install; there were no photos of their configuration. Anyway, they really should include either diagrams or some much better photographs. I'll probably get started on this late Saturday!

RussMcB

Floating an idea here to get people's opinions...

I recently purchased an R&D X-Brace. I have not mounted it yet. I'm wondering if I can improve it by adding simple brackets to the X-Brace's existing brackets, and fabricating two rods like used in the non-X frame stiffeners.

In other words, making a product that combines the two designs.

I have welding/fabrication skills, so that wouldn't be an obstacle.

Good idea? Or flawed?

TIA.

PLRX

This thread is like herpes.

MavsAK

I never got why they simply spot welded the factory frame rails in the first place.

It's such a critical structural member of the car it's not even funny. And the car's price point was already high enough to justify proper welds. (In 1989 the vette cost 31,500..the same as 61,400 today....)

It seems to me, that the frame rails in the C4 are a worst of both worlds, with the way they were put together, vs say a unibody car like a Gen 3 F body. It's obvious the car needed additional structure support front to rear, especially after the last minute decision to not go T Top.

Which means it's not much better than a unibody to start with? I can see how these work, anyone that's put subframe connectors in an F body can tell you the difference is night and day.

These are on my list of mods to get, especially as I like to drive with the targa off spring to fall when I can.

How often do these need readjusting? Do they ever?

DrDyno

HA!