NVR2L8

My Z06 "targa" project continues. The original thread is:

http://forums.corvetteforum.com/show....php?t=2065147

One of my first efforts to reinforce / stiffen the chassis was the purchase of a 3/8" tunnel plate to replace the stock 1/8" tunnel plate. I purchased the plate from Elite Engineering:

http://www.eliteengineeringusa.com/E...ent_Plate.html

The tunnel plate is intended to improve the chassis torsion and deflection, and to reduce heat transfer to the console. I do not want to criticize the product and/or its intended purpose, but it is clear to me that it will not solve my chassis concern.

In my previous thread, MAJ Z06 commented:

I asked one of the engineers that designed the Z06 frame what these after market tunnel plates would do for the Z06 and he said with a bemused tone of voice, "add mass." Aluminum fatigues and then fails, steel doesn't; it's your car do with it what you want.

For the most part, I concur.

On the positive side, the tunnel plate is very strong in torsion, extremely difficult to twist the plate.

On the negative:

1. I placed each end of the tunnel plate on a 2" x 4" and then stood in the middle. The plate deflected almost a full inch. Not acceptable.

2. The tunnel plate is about 42" L x 9" W, and installs between the two center frame rails. Therefore, it only strengthens the torsion of a relatively small portion of the overall chassis.

Any reinforcement that does not solve both torsion and deflection is useless.

I am now moving to the next step.

I will consult with a structural engineer to discuss fabricating a new tunnel plate, one with sides which would be attached to the sides of the frame rails. The strength would function much as an "I-beam" whose strength comes from the vertical portion of the structure. Also, I will be addressing the most appropriate material, aluminum or steel.

I may also have to research additional bracing to connect the center frame rails to the outer frame rails. No doubt about it, this project is not a "quick fix", as long as the goal is the total replacement of the rigidity lost as a result of the removal of the roof.

It is still very possible that the stock Z06 aluminum frame would be sufficient for everyday driving. As stated in the SAE paper written by GM engineers, the aluminum frame (without the roof in place), is within 5% of the strength of the steel frame. If it is assumed that the original GM design is for "worst case" driving conditions, I tend to agree.

As always, your suggestions are welcome.

2SINISTER

Not sure if it would be in line with your goals/needs/desires, but you could look into doing a 4 or 6 point roll cage. That would definitely strengthen the frame of the car. I've seem the custom ones hidden pretty well in other cars. I would imagine one could be hidden reasonably well in a Z06. You could also get it equipped with the swing out arms so that ingress and egress would be easier.

AMGPilot

This was already done by Caravaggio back in 2006. They may be able to help you out with some advice if you want to do this yourself.

Below are the three links that I found from their project car. Not all of the picture links work but all of the info is still there.

Z06 Targa has begun

Latest Z06 targa

Z06 targa finished

NVR2L8

Thanks for the suggestion, but I am not at all a track oriented driver, more into the aesthetic look. Therefore, a roll cage would not be an option in this project.

Thanks for the reply. I have talked to John and traded several e-mails. While his modification is somewhat pricey (approx. $11K), I am sure it is a first class mod. Also, since his system is proprietary, I can clearly understand his reluctance to share information. Just good business practice. I would use his system in a second if I did not have to send my car to Canada. He has also indicated that he may be looking for a location in the U.S. to do installations. I would also jump on this solution if it were not too far from my home.

For now, I will continue to seek expert advice and do research. Hopefully, a feasible solution is not too far down the road.

bob53

NVR2L8,

I think you are headed down the right path. Take a look at the Gennadi system and they do something similar.

http://www.GDGstructures.com/

It appears they started with a thick tunnel plate and then created a cage out of it that allows the exhaust through. This box like structure no doubt has a lot of rigidity. I have shelved the idea right now, but I am very interested in your project. Genaddi seems to have used CF whereas John looks to have used a X-brace as it appears in the photos.

LTC Z06

I'm looking forward to the build.

SB60

I read in a Corvette magazine last winter that he (Caravaggio) was looking at opening a shop in So Cal somewhere? If this is true, I would consider doing this conversion to my Z06 as well. I think there are more people than he realizes out here that would stand in line for a conversion if it was done closer to home. California would be a deal maker for me! If I do it, I want it done right. And I'd also like to know what GM would do to my warranty.

Several people have told me to sell it and buy a Callaway coupe and enjoy a better performer than the Z06. Well that may be true but I bought this car for the 427 engine among other things. Then if you factor in the depreciation and the cost of another new car it is way more than the 11G's for a conversion which is all I want done to the car.

GMuffley

Very informative post. Thanks

Kappa

The tunnel plate probably helps the C5's more than the C6's. The stock one on the C5 seems like it will bend just by looking at it.

Minkster

What does the above mean? If it implies the stock tunnel plate is steel, I don't think it's right. My stock tunnel plate is aluminum. Or is the engineer saying if you replace the tunnel plate, make it a steel one?

NVR2L8

My interpretation of this comment by the GM engineer was that replacing the stock 1/8" aluminum tunnel plate with an aftermarket 3/8" aluminum tunnel plate would be useless because it would increase the mass, but not solve the deflection concern. I now agree 100% with that comment.

I feel certain that the engineer knows that the stock tunnel plates are made of aluminum. I also believe that his comment about steel vs. aluminum was a general comment about frame design and the properties of the material. I do not believe that he was recommending a steel tunnel plate.

I am also certain that a flat steel tunnel plate would not solve the deflection issue, and therefore would not adequately reinforce the aluminum frame rails. Side rails would have to be incorporated into the design to further stiffen the chassis.

MAJ Z06 may want to chime in with his interpretation.

Tavarez

It should still stiffen it up a good amount though no? Or are teh companies like elite engineering just advertising a fasle product?.

NVR2L8

The answer to your question is yes, and no.

I talked to a GM engineer today at the Corvette Homecoming in Bowling Green. He indicated that the primary and immediate concern is torsion, not deflection. The thicker tunnel plates are a significant improvement in torsion. However, the long term concern is the metal fatique of the aluminum frame resulting from hundreds of thousands of deflections.

We discussed the design concept of the chassis, which is designed for "worst case" driving conditions for the projected lifetime of the vehicle, 250,000 miles. This extreme design is required in order for GM to limit the liability that could occur as a result of a significant number of catastrophic frame failures in the future.

The aftermarket tunnel plates available are not intended for converting a Z06 to a "targa". They are advertised to stiffen the chassis (torsion), which they do. Secondly, they are advertised to reduce the heat transmitted to the console. They are also available with a layer of insulation to further reduce heat transfer. I do not have any personal experience regarding the effectiveness of the heat issues, but I believe that this seems logical.