A few things on the Si muffler tip.
You can use an 8th gen Si axel back exhaust on a 9th gen R18. It is direct bolt on. I am now running an 8th gen HFP exhaust I bought from college hills Honda.
Some people get an 9th gen Si exhaust, this is not a direct bolt on. The piping is a larger diameter. You would have to take it to a muffler shop and have them cut the tip off of the 9th gen Si axel back and weld it onto your stock exhaust. Or.... You can do what I did, and how I ran it for over a year, using long bolts with springs and some modified washers to connect the two. I don't recommend this as it caused a small exhaust leak at the connection and just felt too ghetto rigged for my taste.
So the real question is, what are you trying to achieve?
If you just want the look, get the 9th Si exhaust and do the tip swap. Buy one used from someone, I'll be putting mine up for sale soon once I get some free time, and take it to a local shop. Probably looking around $200 total for parts and labor. I would probably make you a better deal on the muffler if you wanted to come out to the island to pick it up as it would save me some trouble.
If you want a better flowing exhaust that will get you a nice sound and less restricted flow, get a 8th gen Si axel back. You can look around for them used or just buy a new one if you don't want to troll and wait. I got my HFP for around $300. I was lazy and didn't want to hunt for a deal. I figured it was still less than buying a takeda or other aftermarket and it's a Honda OEM product. I love it. Great sound and good look. You could probably get something used for $100 - $200 if you put in the time to look. Then depending if you install it yourself you might have additional labor.
Ok, rear sway bar. Lots of options here.
Basic Option 1. You can look for a used one coming off an Si that someone is upgrading. I would look for one coming off a '13 as I believe those were larger than the 12's. Maybe
@Nix or
@webby will chime in with the exact sizes. Again if you don't want to wait and research you can buy them new from college hills Honda. A new one is $40 + shipping.
Basic Option 2. Why not upgrade all together and get something from Eibach or Progress? These will be larger than the Si and provide better results. Yes more expensive but a lot of Si owners are upgrading because the stock one is not enough for performance minded drivers.
I have an Eibach Pro Plus kit, which means I got the front and rear bar, and the Pro kit springs that dropped the car ~1". $560 on tire rack + a 10% rebate. IMO best money spent on this car. Good look, extra added handling and you can still drive it on the streets daily.
http://www.tirerack.com/suspension/...odel=Civic+Sedan&autoYear=2012&autoModClar=LX
You could also just do the rear bar for $165.
First things first, take a second and decide where you are going with this car and what you want to get out of it. That will dictate what you do next. There's a lot of great info posted in other threads. I would read a bunch of them and see what others experiences are doing these upgrades.
. She wants a quiet car.
But hey, this is a Civic. I just want a bit nice sound. Plus I just got a Si rear bumper on my LX. The tip looks ugly as hell.
