About Sway Bars
No, these aren't the things that are bolted inside the car in case you turn it over - those are rollover cages. Anti-roll bars do precisely what their name implies - they combat the body roll of the 350Z on it's suspension as it takes corners. They're also known as stabilizer bars or anti sway bars. Almost all cars have them fitted as standard, but there is usually room for improvement. From the factory the 350Z's sway bars are biased towards ride comfort in order to serve the mass population. Stiffer aftermarket bars will increase the road-holding but you'll get reduced comfort because of it. It's a catch-22 situation. Fiddling with your roll stiffness distribution can make a car uncomfortable to ride in and extremely hard to handle if you get it wrong.

The anti-roll bar is usually connected to the front, lower edge of the bottom suspension joint. It passes through two pivot points under the chassis, usually on the subframe and is attached to the same point on the opposite suspension setup. Effectively, it joins the bottom of the suspension parts together. When you head into a corner, the car begins to roll out of the corner. For example, if you're cornering to the left, the car body rolls to the right. In doing this, it's compressing the suspension on the right hand side.

With a good anti-roll bar, as the lower part of the suspension moves upward relative to the car chassis, it transfers some of that movement to the same component on the other side. In effect, it tries to lift the left suspension component by the same amount. Because this isn't physically possible, the left suspension effectively becomes a fixed point and the anti-roll bar twists along its length because the other end is effectively anchored in place. It's this twisting that provides the resistance to the suspension movement.

This means that the suspension is effectively stiffened, but only when cornering. If you hit a bump in a straight line that lifts both wheels simultaneously, there's no twisting force as the wheels are doing what the swaybar is trying (and failing) to do in the above situation. This means that you can maintain a comfortable ride by running a softer spring, as the anti-roll bar augments the spring's resistance to compression only when turning....which is when you want it stiff.

As for the effect of stiffening one end of the car relative to the other, the stiffer you go the more that end of the car wants to "push". If you stiffen the front anti-roll bar more, the car will want to understeer more. Stiffen the rear more, and the car will oversteer. As such, some manufacturers will choose a swaybar that makes the car more neutral than the understeer-prone OEM.

While it seems like anti-roll bars are negative-free roll stiffening parts, that's not the case. You might be tempted just to leave the factory springs and use ultra-stiff swaybars to give yourself a comfortable ride along with flat cornering. Remember that an anti-roll bar connects the two sides of your suspension together, which means you lose suspension independence. And we all know that independent suspension is far better for ride and handling. What a stiff swaybar means is that bumps affecting only one side of the car get transferred to the other. Hit a pot hole in a straight line, and the car will be more likely to crash through it. One wheel drops into the hole, and instead of just the suspension on one side absorbing it both sides react. Hit a curb in the middle of a corner and you could lift a wheel.

If you run your front and rear swaybars too stiff, you may lose the ability to turn in and put power down. Your car will stop rolling onto its suspension, affecting your suspension geometry's ability to work. This means your tire cannot retain an optimal contact patch onto the road, as the engineers designed it. Net result is that the car feels too skatey.