Can anyone tell me how much of a difference I should expect in loudness or tone by adding HFCs on a 04 coupe with the following mods? I am getting Random Tech HFCs if that makes a diff. Any input is greatly appreciated.

FI exhaust
Ztube Stillen Box
5/16 spacer
Haeaders

 

Not knowing how your state enforces the Federal Clean Air Act, remember you can be held financially responsible for the Felony modification of replacing oem Cats with High Flow units that don't comply.

If your car is sold in future with non oem cats, you can be forced by courts to pay for restoration to oem compliance. Proving who did what is sometime difficult with multiple resells.

Selling a car and supplying a passing emission certificate is emission fraud if the oem cats were replaced with non compliant HFC.

Be sure to keep oem cats for reinstallation prior to a sale. Wash responsibility by selling to a dealer and not a direct retail sell to individuals.

 

with HFCs, your exhaust will sound deeper, more freeflowing, and might have a bit of rasp to it.
at least, that's what i've heard with other people who've had HFCs

 

deeper, not really louder

 

thanks so much all I appreciate the info