Hey everyone! I installed FI HFCs 2 summers ago, unresonated, as i thought that is all i was going to do. They sounded great.
THis summer, i bought the full cat back with 18 inch resonators, hoping it would be a good combo sound wise

So, it sounds amazing when accelerating and at idle, but the interior drone is becoming a little intolerable/embarrasing when i'm holding speeds at 80 km/h and above (especially on the highway). I'm not sure what to do, but I'm thinking to switch back to my stock cats, and keep the catback (with 18 inch resonators), do you think that may solve my problem?

My suspicion is the drone is being caused by the un-resonated HFCs in conjunction with the cat back. Reason I think my HFCs are the culprit in this set up is that I can't find many people complaining of drone or too loud of an exhaust noise with a catback alone (with 18 inch res), and I've also read that RHFC + CBE w/ 18 res has 'zero drone' by some reviewers here.

Hopefully someone here has some insight or experience with this before I decide to go back to stock cats, or if you can think of any alternative solutions I can pursue, like can I still add a resonator to the cats, or swap my cat back resonators with larger ones. Is this still possible after the fact?

PS: I realize they will 'break in' after around 1000 miles and the sound may become softer. But I'm prob just at around 1000 miles since installation, and nothing has changed much

 

From what I have read only way people have not complained about drone is with resonated HFC. Everyone who has installed non resonated HFC said they have drone.
Heres a thread-https://www.myg37.com/forums/g37-sedan/268609-question-about-hfc-s-rhfc-s-and-rasp.html

 

Thats exactly why i went with resonated cats up front, before the catback a year later. Im exceedingly happy wirh this setup now.

Good luck, OP. A set of resonated cats is a reasonable expense considering what you spent on your catback. And you can easily sell your old cats for a couple of bills, im guessing, to offset things a little. You dont really want tp go back to OEM cats... Thats where most of your exhaust power gains come from.

 

OK guys, you answered my quesiton thanks
what i'm going to do is put my stock cats back in, sell the FIs
and order RHFC (they take 3 months anyways)

 

Well hey... Then consider something a little more creative, and look into ARK resonated cats. That Helmholtz design sounds amazing.

 

what do you guys think a fair price for my used FI HFCs is? They are 1 year old. Pulled from a 2010 G37x Sedan
and technically would they fit a 350z or a G37 coupe? Someone is asking me

 

$150 and I'm your man seriously though, I might be interested. PM me when you get a number in mind and let me know.

 

I am in Canada, and it seems 400 CAD is a fair price. That is why I was asking, I have no idea

 

Definitely consider the Z1 HFC. Much more affordable option and they are readily available.

I enjoyed the tone of the Z1 plus the resonated FI system. Albeit I had a 12" resonated system and it still sounded great. No rasp, no drone - perfect in that regard.

Because I was looking for a deeper tone, more burble and a bit louder, I swapped the resonated X-pipe for a non-resonated X-pipe. Great sound combo with the Z1 HFCs, still.

 

Interesting. This reviewer says they are very raspy (is that different than drone?)
https://www.myg37.com/forums/engine-...fc-review.html
Tho elsewhere they seem to get good reviews
I know the cats are the choke point of our ehxaust, so I do want something over stock, I just wish there was an option that provided performance with no extra (or little) sound

 

I am that reviewer and yes it is raspy. Honestly if you don't want rasp you need a rhfc with a new y-pipe. Seems to be the consensus. Ivery learned to live with the Z1 hfc but I'm not going to recommend buying it if you want to cut out some of that extra noise.

 

If you can give me a quote to ship to Baltimore, MD I think we have a deal. You did say the exhaust is for a g37x sedan right?