MarkA - Mark has some track experience with his Si and I think he can attest to the true nature of the understeer of the civic when pushed hard.
The understeer really shows up when turning into a tight corner. If you're entry speed is too high, you turn the wheel and the car just keeps going straight ahead. Then, you get to listen to your tires complain about how hard you're working them, until you either straighten the wheel, or your speed drops enough for the car to start to turn. The 2012+ models have enough torque in the mid rpm range that you can get on the throttle and start getting your speed back just before the apex, but it would be better if you could be going faster at the turn in.
I have a 2012 Si sedan, and I replaced the stock 15 mm rear sway bar with the Progress 22 mm bar. (It's an easy DIY, BTW). It does make a noticeable improvement, but not so much as to cause oversteer. I could probably have used the 24 mm bar. If the 2013 has a thicker bar to begin with, I would definitely go with the 24 mm. The other technique that helps is to stay on the brakes a little longer, as you start to turn, so it keeps more weight on the nose. However, that brings out the next problem with running an Si on the track: the brakes don't have enough cooling. My brakes got so hot, the heat transferred into the wheels, and the little plastic caps with the Honda "H" on them, in the center of the wheel, got soft enough to fall out. I thought it was quite a coincidence, to come across a little silver disk with the H on it, laying on the ground of the paddock, until I realized that it was from my own car! That's a topic for another thread.
For street driving, the car also felt more solid with the 22 mm bar. I haven't driven a 2013 model, so I don't know if the changes they made to the stock Si had the same effect.
