Torque Boxes vs. Frame Connectors
The engineers probably built the unibody to have some flex and
work as a unit front,belly rear and suspension...kinda' like how trucks
with an open sided frame would wiggle and move the cab independently
of the box.This is probably more complicated than we think when it comes
to ride,handling,understeer etc.
...Where are you NuBlu?
Just saw this pop up :D. For future reference, you can "tag" someone if you really want them to see something, pops up as an alert. Just type "@" before the username ie,
@ir3333 . The site even suggests autofills from the username list after a few letters.
Um yeah, chassis engineering is a super complicated deal, that's why guys with engineering degrees design this stuff. You do want your car to have some flex, because if you have too little flex you break stuff, cracks appear at joints, etc. But, the same thing can happen from too much flex, you overstress or overflex the materials and you guessed it, cracks appear. For a totally different reason, but you can get cracks from too much or too little flex. You have to balance this to the use of the chassis, how much power you have, etc with the strength of the chassis and how much flex it can withstand.
Since most of use have doubled or more the amount of power in these cars, it goes to reason you need a stiffer chassis. Same thing with upgrading the suspension. The old bias plys and floppy stock torsion bars don't translate a lot of force to the chassis, so, back then you didn't need a very stiff chassis because the OE suspension doesn't load the chassis all that much. So of course the factory isn't going to do frame connectors (or a full frame) or even torque boxes if they weren't really needed, just adds expense. And in the 60's and 70's, they weren't really needed for the amount of grip and power these cars had. At least not to meet the "life expectancy" of these cars that the factory designed for.
Now of course it's totally different. Even just adding radial tires makes a big difference, which is why I would never put anything smaller than a 1" torsion bar on a car anymore. Even with not so grippy BFG T/A's you have far better grip than bias plys, so, you get more force to the suspension and chassis. It's all a balancing game between grip, power, and chassis stiffness.
The argument between tubular subframe connectors, weld to floor connectors like the US cartool ones, homebuilt through the floor connectors has happened a whole bunch on this site, and I've been drawn into it a few times. The bottom line is, unless you do a finite element analysis on the whole chassis, no one is going to know which style is "best". Even the little bolt-in Mopar Performance tubular connecters make a difference when welded in. Are they as stiff as a set of US Cartool connectors? Not likely. Are they as good as a set of 1.5"x3" tubular connectors like I run that don't go through the floor? Probably not. Are those as stiff as a 2x3" tubular connector that goes through the floor? Who knows. The thing is, there's a limit to how stiff a set of frame connectors can make a car. Only so much force is translated along those frame members. So at some point the strength of the connector surpasses what the chassis carries at those points and you've gone into overkill. But without an FEA, who knows what that is.
For me, the bottom line is any frame connector improves the stiffness of the chassis some. Some are no doubt better than others, but for a given application we have no idea which one is actually better. I use a set of tubular 1.5"x3"x.120 connectors on my car that I build myself, with large anchor plates that overlap a whole bunch of the rear rails and the torsion bar crossmember. The difference was noticeable. Torque boxes help a bunch too, by boxing the corners of the chassis where a lot of load and twist occurs. Even the factory knew that and added them for the 'verts and high horsepower cars. So, for me I think ALL of these cars could use torque boxes and frame connectors. Improvements in tires and suspension make them even more necessary. Anything is better than nothing, and unless you do an FEA no one is going to know what's "best", because you can make the subframe connecters stronger than the amount of force the chassis will send to them (and stronger than the chassis they're attached to!). And you can even make a car "too stiff" too, although that's kinda unlikely in this case. That's just my .02.
