So after looking into high flow cats I was thrown off quite a bit regarding the 350z exhaust in general. I purchased the car with a Tanabe hyper medallion on it.

Questions:

-So to my understanding this exhaust did NOT include the y-pipe and is currently connected to the stock y pipe and cats? Only reason why I ask is because there are all these aftermarket y pipes and unless the other owner threw aftermarket hfc on a "tanabe" y-pipe (if it exists with this exhaust) because on my recent emissions test it was stated that cats were present.
-There are two catalytic converters
-Why are they so expensive? You couldn't just use standard hfc like from magnaflow or flowmasters?
-What's the diameter on these? 2.5?

I know that a lot of this could've been answered by just looking underneath the car but it's very low and my jack and stands aren't at my current locations.

Much appreciated,
Vang

 

the tanabe exhaust does not come with a y pipe, i know that part of your question. and yes catalytic converters are quite expensive, i wouldnt spend more than $450 on them. Berk is what most people go with.

 

Bumped for new questions in original post

 

Tanabe Exhaust:
Piping Diameter: 70mm

Tanabe y pipe:
The piping is 60mm and joints to a single 70mm outlet

 

Our Stock Manifolds have a 2.25 Collector. You can use any Test Pipe / Hi Flow Cats that has a 2.25 Collector with a OD of 2.50 that connects to the stock y-pipe or aftermarket y-pipe. Some people run the 2.25 ID & 2.50 OD which is perceftly fine.