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Definitive HFC Thread

galaxy

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So I had a question about high flow cats that I don't think has been answered...

Setting aside any emissions inspection requirements, are high flow cats a nice balance on being too loud and dealing with the smell of no cats? Seems like more often than not, I see guys putting cats back on or making other changes because 1) it's toooo loud, or 2) they don't like the smell.

I'm wondering if high flows address the smell (not that I'm too worried about that) and add additional volume with a bit of balance between cats or no cats?? Thoughts? Sounds?
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Hack

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So I had a question about high flow cats that I don't think has been answered...

Setting aside any emissions inspection requirements, are high flow cats a nice balance on being too loud and dealing with the smell of no cats? Seems like more often than not, I see guys putting cats back on or making other changes because 1) it's toooo loud, or 2) they don't like the smell.

I'm wondering if high flows address the smell (not that I'm too worried about that) and add additional volume with a bit of balance between cats or no cats?? Thoughts? Sounds?
I had a set of high flow Magnaflow cats in a 1987 Fox Mustang with a 408 Cleveland swap, long tube headers and 3 inch exhaust. I ran them because I prefer not to pollute if I can avoid it. The exhaust was very free flowing (and loud), but it had straight through mufflers as well. Didn't have a problem with smell in that application - even when I had a very safe and rich initial tune on it. I'd like to give you a definitive answer, but frankly I think the answer to your questions will depend on the exact cat and the application.

Here's a photo. It was a little crazy with the Trick Flow Box R intake sticking through the hood. And a tight fit in the car.

Clevo in 87.JPG
 
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galaxy

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B-Line Motorsports now makes high flow cats for the GT350
https://www.blinemotorsports.com/
Yup! ā€˜ā€˜Tis the reason I started this thread. Always been worried no cats is just toooo dang loud and maybe even not a good quality sound. Always thought HFCs might be a nice compromise. Iā€™m gonna roll the dice on these...as soon as they come out with a complimenting x-pipe.
 

honeybadger

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I can tell you that no cats sounds terrible on this car unless you're on a race track at WOT. My car is DEAFENING and it's downright painful on pit out. Full throttle on track and everyone is all smiles, tho.

If street driven, I would never recommend it.
 

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i have no cats & car sounds/smells awesome.
 

Bulldogs22

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Yup! ā€˜ā€˜Tis the reason I started this thread. Always been worried no cats is just toooo dang loud and maybe even not a good quality sound. Always thought HFCs might be a nice compromise. Iā€™m gonna roll the dice on these...as soon as they come out with a complimenting x-pipe.
I assume no other x-pipes would be compatible with these like for instance a corsa x pipe? This seems like a nice cheaper alternative than long tube headers to get sound/performance and much easier install.
 

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I have recently installed Kooks headers with their Green cats, and they do a good job of keeping the smell down. I only notice it when starting cold. They won't keep from triggering your CEL though, so if inspections are an issue for you, then there's that. As for sound, I haven't run it without cats, so I don't have a comparison, but I will tell you that I have added two resonators per pipe (one 10", one 15"), and the car is still pretty loud for street use. If the GT350 didn't have the selectable valve, I would still be looking for additional ways to quiet the exhaust. However, at 6k on up, the car just sings. I have a friend with a Ferrari 458, and with my setup, the cars sound quite similar at those RPM levels.
 

Angry50

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has anyone done cat deletes but leave the resonators in? this is the method i want to do. cat delete and e85 tune i think would make the car awesome
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