So with stiffer TBs you can end up bouncing across a rough corner as the suspension will bounce the weight of the car upward at the bumps and the wheel cannot travel down quick enough as it hits the next bump and does the same.
Bouncing across rough roads is a combination of too much dampening on the compression side of the shock in correlation with the spring (torsion bar). That's why KYBs are bad choices for stiff bars (stiff shock + stiff bars = trips to dentist to replace fillings shaken out)
This is not entirely accurate. The stiffer the bar the
faster they tend to travel if they are deflected, since they will exert more force to return the wheel to neutral. They also tend to deflect less, which results in a rougher ride, since the entire chassis moves instead of the spring. Now of course as a spring they will actually push the wheel past neutral on the return and continue to oscillate, which is why shocks are so important to dampen the spring action.
What you want is for your spring to be fairly close to "critically dampened", which means that the spring/shock combination deflects once and returns almost exactly to neutral with no oscillation. Over-dampened leads to a really stiff ride and even more limited wheel travel, under-dampened means too much oscillation and your car bouncing up and down long after the pothole has passed. The stiffer the spring is the
faster the dampening of the shock has to be, so its not just the stiffness of the shock, but how fast that dampening takes place. As the springs get stiffer, the wheel moves faster, and the valving of the shock has to be matched so the shocks react in time. The KYB's problem isn't just having too much dampening, the valving is critical, and on cheaper store bought shocks its more likely that the valving isn't up to par, or matched well to your particular set up. Which is why really good shocks are adjustable in compression speed and dampening, and really expensive.
The most important thing with any choice in suspension is to match the
entire system. This takes everything into account-springs, shocks, sway bars, bushings, and tires. Tires are a huge factor. Modern tires provide MUCH more traction, which keeps the car from skidding/hopping, which in turn allows a stiffer spring. Since the tires will stay stuck to the road they transfer more load to the springs, so the springs need to be stiffer and the shock's valving faster.
If you plan on running stock size tires with more "period correct" harder tire compounds, stick with softer bars and shocks, balance them with larger sway bars to control body roll in the corners, and call it good. The softer bars and shocks will give a smoother ride and the sway bars will provide a higher effective spring rate in the corners. This also applies to rough roads. The softer bars allow more wheel travel, so the wheel stays in contact with the road better (the whole point of suspension). Which is why dirt bikes have soft springs with loads of travel, the wheel stays on the ground more than if the springs were stiffer, reducing that "bouncing". Stiffer bars reduce the travel, so the car bounces and skips across the rough road since the suspension won't deflect enough to take up the bumps.
If you want to run wide modern tires and do some corner carving, you can get away with much larger torsion bars, stiffer shocks with faster valving and possibly smaller sway bars. The tires will stick, transfer a ton more energy to the suspension, and the larger bars and better shocks will keep them planted. But as mentioned, the larger bars will reduce travel, so smoother roads are needed if you want to avoid skipping right off the road when you hit something bigger than your suspension can absorb with its more limited travel.
It all really comes down to matching the suspension to what you do with the car, which is the bottom line. For the best results, you need to consider the type of driving you do and your driving ability, the roads you drive, and how you want to set up your car.
This is all just a lot of technical crap though and probably WAAAAAYYYY deeper than anyone wanted to get (I'm an engineer, sue me, I over-analyze). Which is why there's a lot of merit to looking at what "most folks" do. And with a big block car set up for "normalish" driving for a musclecar, a set of .92 to 1" torsion bars, mid range shocks, and stock-ish sized torsion bars with slightly larger and better tires than stock is a pretty good choice for "most" folks. I lean to larger bars, but I like to drive hard in the corners too and don't mind oversteering a little, so that's my preference.
