1. It will throw a CEL, you can either get the electrical fix or the mechanical fix.

Electrical- You splice a resistor into the O2 sensor
Mechanical- screw two sparkplug extenders together, and then screw the O2 sensor into the extenders and then screw it into the pipe. (I have this one and it works great, I didn't feel like splicing wires. need more details pm me, and I could probably make you one)

2. You will probably notice that it will be alittle louder but not by too much, don't worry it won't be too loud.

3. Yes it will match up with Greddy EVO, and the Borla Hush I think, most likely.

Raymond

 

That is a good deal but that downpipe does not have a bellmouth or divorced wastegate so you will not get the gains you could with one that has one or the other. Here is a pic http://www.ss-ms.com/shopping/cart/c...cat=283&page=1. Compare that to the Helix with a bellmouth design http://www.ss-ms.com/shopping/cart/c...cat=283&page=1.

 

I have the HKS cuz I got it cheap. you will need gaskets to install.
It will throw a cell, you can do what esracer said, but you can also just get a cel fix if you don't mind spliced wires.

It's barely any louder, unless you're like me(retarded) and had a leak and didn't fix it until I got a catback to go with it since it sounded cool. haha yes...i know...retarded...

It'll fit I think all USDM exhausts. However, it is not that great(people say it's the crappiest) because of it's flat-plate design. Better downpipes have a bellmouth design which allows for better flow from the wastegate to pass through without turbulence. I plan to take it to a muffler shop or something and weld on a divorced pipe for the wastegate to go through, but unless you want to run massive power, it shouldn't affect it that much.

edit:
gaskets and cel fix are usually sold with the downpipe. but I just read you are getting it from a friend. Subydude and other vendors sell gaskets, as well as dealerships, but I'm not sure where to get a cel fix. Mine came with my dp. sorry.