I was wondering if I remove my resonator and muffler and get high flow cats if it would be good performance wise and also would I be able to pass emissions?

 

Emissions no depending on your state...California you can forget it...

 

What about in Scottsdale Arizona?

 

Not sure about Arizona. Here in Texas they wont, unless you through an extrea $20 bucks there way at certain places performance wise your not really going to see any gains.

 

Wouldn't it be better than a stillen or hks exhaust because your not restricting the airflow at all with a test pipe which means more hp right?

 

How are you not going to see any gains with HFC's or test pipes over OEM cats??? Opening up your exhaust is one of the most basic performance mods you can do

 

Test pipes replace the OEM catalytic converters (cats) which are the part that connect the cat-back exhaust to the headers... They are not a replacement for an exhaust.

 

The best combo would be test pipes with some aftermarket exhaust. Louder, less restricted, and probably lighter.

I have a Greddy catback and now I'm in the market for test pipes or HFCs.

 

Right now I removed the muffler and it has a deep and loud sound. I wanted to know if it was worth removing the resonator and the cats or getting high flow cats would be worth it or not?

 

...You just took the muffler off? Or did you replace it with something?

IMO high flow cats are definitely worth it.

 

If its just HFC or test pipes that not really enough on are cars see a gain power wise. Sounds yes but not really power. With a full exhaust than thats a different story.

 

I swapped out my OEM cats for HFC's before I got an exhaust and definitely noticed a difference.

 

Wouldn't the exhaust post-cat be more restrictive if you had high-flow cats but stock cat-back exhaust?

 

um, no. The cats are the most restrictive part of the exhaust. (look at the OEM ones and you'll understand why)

Replace either the cats OR the cat-back and you will notice improvements.
Replace both and you will notice more improvements.

But yes, the stock cat-back is still restrictive if you just swap out the cats but you've removed a bunch of the restriction and its a lot easier for the engine to push the exhaust out.

 

Yeah, I understand that the cats are very restrictive/dense... I'm not all too familiar with the G35 exhaust set up yet (noob to the Gs ). But you know, closer to the exhaust valves you are in the system, the hotter the exhaust, so I would think the further it gets away and cools off (and then expands) you would want the piping to get progressively bigger, and so I was thinking that if HFCs for the Gs have bigger inner diameters than OEM, and then you go from let's say a 3" HFC to a 2.25" catback section, it would be a restriction in the system.

But, if the cat honeycombs are a much bigger impediment to flow than just sheer diameter, that would make sense.