the front makes a more noticable difference imo

 

Strut bars are not necessarily the first thing I'd upgrade on a suspension setup. With that being said, it's going to depend on what you'd like the car to do.

As with most suspension mods, if you're trying to get the car to rotate more (go from under to neutral/oversteer) then stiffen up the rear.

If you're trying to eliminate oversteer or twitchyness, stiffen up the front.

 

IF you have a wagon, the rear would make a considerable difference. The sedan won't benefit as much. I would get an adjustable rear sway bar first, if you don't have one. Some end links too.

 

strut bars don't do anything. i had one on my integra. if you're talking swaybars get the rear.

 

i say rear too... any rear STB will be okay. if you get a Front bar gewt a whiteline ksb599

 

What year is the Civic Si?

If it is a 99 or 00 model then the front should have a decent strut bar and sway bar. The rear lower sway bar is what you want to increase. The best way to go is to get an Integra Type R 22 mm rear swaybar with the beaks kit. Will make a huge difference in the way the car handles.

I would think the 03s would be the same deal but since it is a completely different car then it's hard to say. The main thing you want out of a FWD car is rotation from the rear which is what the larger rear swaybar will do for you.