High flow cat direct replacement (no headers)
Thread Starter
Burning Brakes
Joined: Aug 2007
Posts: 839
Likes: 15
From: Allentown PA
High flow cat direct replacement (no headers)
Hey guys, I'm curious what the sound difference would be on a NPP exhaust with high flow cats only and no headers. Looking for a direct bolt on, would this make the exhaust note louder?
Racer
Joined: Jul 2008
Posts: 409
Likes: 8
From: VA
On my 2008 coupe, random tech. HFCs added to a GM performance off-road exhaust (Borla stinger) made the sound roughly 5% louder. It was higher pitched, not quite as deep, like decreasing the bass slightly and increasing the treble. Honestly, HFCs are not worth it. You get maybe 8 whp, and they will throw o2 sensor codes every single day, sometimes multiple times a day. You can add spacers to the o2 sensors to desensitize them, but even that isn't a guarantee. I wouldn't get them unless you're trying to get every bolt on imaginable without a tune. And you'll probably have to get the spacers, I think others here have said that they are generic spark plug spacers for GM V8s.
Melting Slicks
Joined: Sep 2008
Posts: 2,286
Likes: 4
Just get the headers too. You won't be sorry but get a tune too so you won't receive any codes. I left the stock mufflers on mine because after the headers with hi-flo cats and x-pipe, it was too loud with my Magnaflow cat backs for my liking. You have the NPP's so your perfect. Even with the stock cans, it gets deep and loud when you hit the gas but is whisper quiet around town.
Jeff
Jeff
Le Mans Master
Joined: Oct 2000
Posts: 6,499
Likes: 717
From: Sausalito CA
Yes, headers is the answer.
I have these cats, can't say about performance, and sound wise my car is quiet so no comment.
As I recall the HFC were not inexpensive however they are bolt on.
In regards to installation, make sure you spray liquid wrench (or the like) onto the exhuast maniford studs (for a few days) before your start removing the nuts...else you make break a stud. Some heat may help in removing the nut too.
Yet, I will comment on the positive weight savings over the OEM.
Also, I have never had codes...ever.
I have these cats, can't say about performance, and sound wise my car is quiet so no comment.
As I recall the HFC were not inexpensive however they are bolt on.
In regards to installation, make sure you spray liquid wrench (or the like) onto the exhuast maniford studs (for a few days) before your start removing the nuts...else you make break a stud. Some heat may help in removing the nut too.
Yet, I will comment on the positive weight savings over the OEM.
Also, I have never had codes...ever.
