oh s***...so you guys recommend me to order that extenders too??

well if you order them ahead of time and install em ahead of times its easier and possibly cheaper via labor.

but no one can really tell you 100% that you will need em. and no one can tell you 100% that you wont need em. : /

i order the extenders for like $15 off of ebay but while lurking around oreillys one day i seen a set called "spark plug extenders" same exact thing for like $4.99

awwwwww damn! haha I hate this kind of situation! I hope it works well without them! :(

so Stells, you recommend me to order "spark plug extenders" ??

I found some 02 sensor extenders in Ebay.
O2 02 Oxygen sensor extenders 2 Test pipe HHO Hydrogen | eBay
Will this fit?? drilled out 1/2 in and are 18mm 02 sensor extenders. seems the right size.

hard to comment on an ebay item unless its one of the few rare reputable sellers and they are selling a reputable brand.

I do know for a fact the z1 extensions work and they are 35$. its not quite 9.99 but again :p your in the situation where its hard to really say 1 way or the other.

Hey Daisuke, where can I buy that z1 extensions? I want to see the product :)

I think what I will do is just install the hfc without the extenders, and if I'm fine with CEL, I will not buy extenders. what about that??

so
ERZ performance CEL Eliminator Fix O2 Sensor Housing , Subaru WRX STI performance parts. Subaru Header Downpipe and Up pipe vs Z1 Oxygen Sensor Extension Bungs (Pair) ???????

I aint the expert on this one. the ERZ looks interesting. Installing it may be a pain since you gotta make sure that the direction you have it pointed, will also make it tight and then the o2 sensor can screw into that as well without interfering with the bracket or anything else. Thats what i would worry about. the HFC / Tp that already have the bend in it ussuall account for fitment when they design it, this would be a bit diff.

so I think I should install it first and if it's fine, i won't have to buy extenders

might be the best way. if you plan on a tune get that too.

ok thanks for the helps Daisuke. I really appreciated! :)