The tunnel plate won't help the chassis but it might help with the body flexing and moving relative to the chassis. I agree the tighter feeling would improve driver confidence. But if you really want a stiffer chassis, you need to stiffen the FRAME.

 

Whether you make all the mods listed in this thread or none of them, this is the single most important post in your thread. You have to know where you're at and where you're going WRT to your alignment settings. Whether it's toe, camber, or caster, the affect each positive or negative adjustment has on the front or the rear WRT handling dynamics is so very important to know. Every mod you make to your suspension will change the handling dynamics requiring new alignment settings. Those mods run from the obvious like springs and stabilizer bars to the not so obvious like poly bushings or stiffer stabilizer bar links or even tires. If I had your situation, I'd look at the rear toe setting first. If it has toe out or it's at zero toe, you've found your problem and you need to go to toe in. If it has toe in, I'd dial in a little more toe in if it's not at the max allowed by the specs. Next check rear camber to see if it's out of spec. Again, if you find zero or positive camber, you've found your problem. Just remember when you adjust camber (and caster on the front), you change the toe setting. If you're not worried about tire wear, don't hesitate to venture outside of the specs for even more grip.

The ideal thing is learn how to do alignments yourself so you're not paying $100 every time you feel the need to tweak a setting. Kind of like the old saying about the man and fish...give a man a fish and he'll eat good for one night, teach a man to fish and he'll eat good forever. I do all my alignments myself and have taught others, it's way too easy with cheap/simple tools (carpenters square, dial caliper, 3'-4' level, cloth tape measure, and calculator). I always start with a "baseline" setting (varies by car/mods/driver) and then dial it in from there to achieve maximum grip, excellent turn-in, balanced/predictable handling, good manners at the limit to inspire confidence, and of course even wear. I even have different alignments for high and low speed courses.

Trust what the guy above says, there is no better mod for your car than a good alignment. If you take it some place, make sure the shop caters to road racers and make sure you tell them what the car is doing now and what you want it to do. Like C6400hp says, "you will find a massive difference in handling dynamics".

 

I love my cheap Hotchkiss.... and my good alignment

 

I have added coil overs with remote reservoirs and 1 1/4 " sway bars. A 4 corner balance is critical. adjusting the weight of each tire has on road surface. after this upgrade your car will feel like its following a rail. tight as you can imagine. I have a vert and never did tunnel. but now this thread has me thinking. any little enhancements you can get will give you that edge. and confidence is also key. once you dont trust your car forget about pushing it to the limit you always tend to back off.

 

I agree with the post above talking about rear toe in. While I'm not expert, I've had a Vette for a while so here's a few thoughts from me from my own experiences:
1) I'm assuming your tires were warm but if for some reason you felt looseness when you first start driving, the tires could have been a little cold. This is more true the colder it gets outside.
2) How smooth are you on/off the throttle. Goose the throttle and you do invite the rear to come around.
3) I've always found the Vette a little tail happy so that could be its natural tendency.
4) Sway bars are always fun to adjust but you can always increase your oversteer problem if you don't change your swaybars for the better. Since you would like the car to be less loose, what you are essentially trying to do is soften the rear (after you look into alignment). To soften the rear, you can take out a little air from the rear tires, add some air to the front tires, stiffen (usually means larger) the front sway bar, soften (usually means smaller) the rear. If you change front and rear sway bars, make sure that you increase the stiffness of the front more than the back. You can change your shocks and then you have to reassess if your oversteer got better or worse. You can even change your springs so that the net change leaves the rear less stiffly sprung. I'd start with tire pressures and alignment cause they're easy.

Rear toe - slightly in should help as the poster above said. I'd just be careful and watch your tire wear if you put a lot of it in. Also, too much could adversely affect your handling too. So its a nice fine balance...

 

Thanks for everyone's help. You guys have given me some great info. I just got in a new tunnel plate (hopefully that will help with the little bit of creaking I have at times too) and hotchkiss sway bars. Those will be going on soon. After those are done I'm going to try and find a good shop for doing my alignment. I will also play around with the tire pressure a bit more. The next track I am running at (Autobahn) looks like it will have another nice sweeper so that should give me a good opportunity to test the modifications and even play with different tire pressure settings.
I think the minor changes that will be made will make a noticeable difference in how the back end feels. The only question I have left is about ride height. What is everyone's opinion about that? I've heard some say that it really won't make any difference and that if I change it too much it could actually give me an adverse effect.

 

Well as an update... I stayed up late last night on got on my new rotors, pads, mufflers, tunnel plate, and the Hotchkiss sway bar (only got rear done so far). I haven't gotten it to the track yet but I can already tell a major difference in the way it takes the long turns. I drove it in to work today and on the exit ramp the car would usually start to squeel and feel on edge when I hit .8g. Today when I took it and hit .8g it felt like it still had a lot left and wasn't being pushed all that hard. Not exactly scientific or race track conditions, but it is still a turn I'm familiar with and there is quite a difference with the new sway bars.