Volume difference stock cats vs FI HFC
 

I just bought a Z with the Fast Intentions cat back exhaust (18” resonators) and resonated high flow cats. The car is a little loud for me, does anyone know how much quieter it would be if I returned it to stock cats? The cats look a bit corroded, is there still resale/trade value?

Attachment 146594

The metal is worth something for sure. Check out a recycler or metal reseller. May or may not be more than the secondary sale market...

If it's the cabin noise you are concerned about then it won't be much quieter. Sound deadening is the way to go.

I went from unresonated FI exhaust with cats and switched to TPs. Crazy difference in noise; I like it. The stock cats are quiet af compared to open flow. No experience with HFCs tho :shrug:

Stock cats would definitely be quieter, no question. However, this may not solve drone problems at certain RPM,s. That would depend on your cat back.

I run the 18" resonated FI exhaust on stock cats. Not loud at all in my opinion. I wanted something quieter after my previous car had a loud *** exhaust. Very happy.

Drone does not come from the cats
 

The overall noise will decrease by going oem cats but it won't change the drone. Drone comes from the exhaust system actually. Only way to fix would be to insulate the cabin and add rubber cushions where you bolt the exhaust system. I don't like the drone either but I learned to cope with it. One should pick their battle since it's a tuner car. Do you want to go fast or have a smooth and easy ride? If you want comfort then go back bone stock.

Thanks for the input. I think I can get used to the sound but was wondering if the amplitude of the sound was decreased. I drove yesterday for about an hour and a half on the highway and it was pretty fatiguing. That said, I looked up the price for stock cats and was very surprised to find out that they're twice as expensive as the FI HFCs! I do enjoy the way the car sounds in the parking garage in first going up to 4k RPMs!

I'll probably take a couple months and see if I get used to it or go back to stock cats. I was reading on the tuning section last night about running lean after breather mods with no tune and now that has me paranoid. I have no idea if the car was tuned but the previous owner said he bought the car with all the mods already on it and that was about 16,000 miles ago. There aren't any warning lights so I'd imagine things are decently sorted but I need to start trying to confirm what maintenance I need to make sure has been done since it's got 76,000 miles on the clock.

You need sound deadening. The hatch echo's like an auditorium.

Sound deadening is a band-aid for "too much noise created in the first place".

I have an HKS Hi-Power catback. It uses Helmholtz resonators to suppress the drone frequency (there is ZERO drone). It is very quiet and docile in the cabin at low RPM / light throttle loads (very close to the stock exhaust) but it comes alive significantly when you put your foot down and has a very rich, harmonious roar to it. It's louder outside the car than from inside the cabin, for sure. If you drive it gently you will forget you have an aftermarket exhaust, it's that good.

Stock Z, no additional sound deadening and I HATE overly noisy exhausts. HKS have done some brilliant engineering for this one.