Performance with Catalytic Converters?

[richtersand]

I am debating adding catalytic converters for my upcoming Coyote 5.0 build, mostly to cut down on noise (reacting to Paul's recent comment that it starts loud and gets louder). I would prefer to avoid ear plugs if at all possible :)

I haven't found much discussion on this, so I thought I would ask:

1) How much can I expect this to help with reducing the sound? Would Gas'n pipes do a better job lowering the volume?

2) How much performance would I lose?

Thanks in advance!

Cheers,
Matt

[Alan_C]

When I built my MK IV with a 4.6L DOHC I used the Cat/J-pipes and Gas-N side pipes. Great sound without needing ear plugs. You could have a conversation with your passenger so long as you were driving normally. When you get on the go pedal, it would get louder, but still tolerable. After I sold the car, the 2nd owner put the car on a dyno, 299 HP to rear tires from an engine that was internally stock. So I would suggest that the Cats did not hurt HP too much. I liked the combination as I felt the Cats acted as a pre-muffler to the side pipes. The Gas-N side pipes have a nice tone and are beautifully made. Although not a Coyote, the 4.6L was its predecessor.

[edwardb]

I'm assuming it's me you're referring to. Couple of comments: The "loud and get louder" comment is meant toward the stock side pipes. I personally haven't experienced it because I haven't left them on long enough to find out. They were just too loud to begin with for my taste. But multiple reports of the stock side pipes burning out over some thousands of miles. Not sure of the exact amount. And in the process of course getting even louder. I've been super pleased with Gas-N pipes. Although dB-wise not much quieter. But a much mellower tone and seems to hold up. My Mk4 with Gas-N pipes is approaching 7K miles (not a ton, I realize) but sounds like the day it was new. Others have reported the same thing.

Regarding cats, I personally haven't installed them. But many report they definitely make things a bit quieter. I can't give any actual data about power loss, but don't think it's significant. I have a local friend with a Coyote powered Superformance with cats and an undercar exhaust. Helped him with a Lund Racing tune so had the car for a bit and drove it while tuning. It certainly doesn't lack for power. The combination of cats and undercar exhaust made it almost daily driver quiet.

But a reaction to one point you made. You said you want it quieter so you don't have to wear ear plugs. Please reconsider this. The sound of the exhaust is almost unheard in my Coyote powered Mk4 when cruising in 5th at highway speeds. Regardless of what side pipes, cats, whatever, can't imagine it being much quieter. But the interior noise level in the open top car is still in the 90's dB range. I've monitored it several times use an app on my iPhone. Combination of engine sound, tires on the road, wind, traffic, you name it. These cars are loud not matter what. In that environment, you should wear some kind of ear protection and just make it part of your driving experience. Like buckling up the harness. Long term damage can result at those levels.

[walt mckenna]

I am debating adding catalytic converters for my upcoming Coyote 5.0 build, mostly to cut down on noise (reacting to Paul's recent comment that it starts loud and gets louder). I would prefer to avoid ear plugs if at all possible :)

I haven't found much discussion on this, so I thought I would ask:

1) How much can I expect this to help with reducing the sound? Would Gas'n pipes do a better job lowering the volume?

2) How much performance would I lose?

Thanks in advance!

Cheers,
Matt

I drove my car without CATS for a couple of years before adding them. The main reason was the smell; my wife hated the smell and wouldn't ride in the car until the CATS were installed. My subjective opinion on noise is that it is definitely quieter and as far as power, I can't tell the difference.

[Bobby Doug]

If you value your hearing WEAR earplugs. At highway speeds the wind noise is almost as bad as the exhaust. Just the nature of the beast. Happy motoring.

[phileas_fogg]

Take it from a guy who now has permanent ringing in his ears (from wearing earplugs that weren't adequate for the task), wear hearing protection! My audiologist told me the best hearing protection is (1) over-the-ear muffs, (2) custom ear plugs, and (3) the cheapie foam ear plugs you buy by the bag at the home improvement stores.


John

[GTBradley]

I’m going to do this very thing at some point. While loud is cool at car events, I get tired of it on longer road trips. The research I’ve done shows little to no power loss with high-flow cats. And the new headercat that FFR sells contains a cat and O2 sensor in the same stainless, long tube header that goes on the Coyote.

[Dewey McBride]

When I built my MK IV with a 4.6L DOHC I used the Cat/J-pipes and Gas-N side pipes. Great sound without needing ear plugs. You could have a conversation with your passenger so long as you were driving normally. When you get on the go pedal, it would get louder, but still tolerable. After I sold the car, the 2nd owner put the car on a dyno, 299 HP to rear tires from an engine that was internally stock. So I would suggest that the Cats did not hurt HP too much. I liked the combination as I felt the Cats acted as a pre-muffler to the side pipes. The Gas-N side pipes have a nice tone and are beautifully made. Although not a Coyote, the 4.6L was its predecessor.

And now that I have 12,000 miles on the car, it's just as quite as the day I picked it up from Alan_C with 4,000 miles on it. When i travel with the Cobra Club everyone always comments that it's very quiet for a Cobra. Non-Cobra owners still think it's loud. The GasN pipes give it a great low tone and the CAT's tone it down just a bit more. Bonus, I think the CAT's also keep your exhaust pipes from getting "as" hot. I really don't think there's much hp loss if that's what you're worried about.

[JohnK]

And now that I have 12,000 miles on the car, it's just as quite as the day I picked it up from Alan_C with 4,000 miles on it. When i travel with the Cobra Club everyone always comments that it's very quiet for a Cobra. Non-Cobra owners still think it's loud. The GasN pipes give it a great low tone and the CAT's tone it down just a bit more. Bonus, I think the CAT's also keep your exhaust pipes from getting "as" hot. I really don't think there's much hp loss if that's what you're worried about.

Thanks for sharing your experience. That's very helpful. How's the heat in the footboxes with the cats sitting right next to them? I'm planning to install the GP headers with built-in cats on my build, and I was thinking of putting a layer of Second Skin Mega Block (https://www.secondskinaudio.com/heat-insulation/mega-block) on the outside of the lower part of the footboxes to supplement the Lizard Skin heat + sound insulation I'll be spraying on the inside, to keep the heat from the cats down. I'll also be ceramic coating the headers and side pipes. I'd love to hear your thoughts on any additional heat from the cats.

[richtersand]

Thanks everyone, great discussion.

I found this video with somewhat scientific side-by-side comparison. Given what everyone says about Gas’N being quieter I was surprised to see they registered marginally higher.
https://youtu.be/plP1ecBy8F0

I’m also very interested to see feedback on JohnK’s post.

Cheers,
Matt

[walt mckenna]

Thanks for sharing your experience. That's very helpful. How's the heat in the footboxes with the cats sitting right next to them? I'm planning to install the GP headers with built-in cats on my build, and I was thinking of putting a layer of Second Skin Mega Block (https://www.secondskinaudio.com/heat-insulation/mega-block) on the outside of the lower part of the footboxes to supplement the Lizard Skin heat + sound insulation I'll be spraying on the inside, to keep the heat from the cats down. I'll also be ceramic coating the headers and side pipes. I'd love to hear your thoughts on any additional heat from the cats.

I installed insulation on both sides of the footboxes and firewall and as a result, get no discernible heat from the CATS/engine bay. I also did not close the gap between the top of the radiator and body which helps with engine bay heat.

[CraigS]

Several comments I have read here is that the Gas-n pipes may be only marginally quieter but that the type of sound is much nicer. I would do cats in a heartbeat. I don't know what is available for the Coyote in an FFR but a quick search at Summit will yield plenty of high flow cats. I have no data to support this but my take is this. Like a lot of automotive things when they first arrive (efi, ABS), they have short comings. I remember many cats being replaced because they either clogged up or lost effectiveness. But in the last 10-15 yrs they have improved tremendously. BTW, if you happen to lose 15hp, you will never notice it.

[rich grsc]

Several comments I have read here is that the Gas-n pipes may be only marginally quieter but that the type of sound is much nicer. I would do cats in a heartbeat. I don't know what is available for the Coyote in an FFR but a quick search at Summit will yield plenty of high flow cats. I have no data to support this but my take is this. Like a lot of automotive things when they first arrive (efi, ABS), they have short comings. I remember many cats being replaced because they either clogged up or lost effectiveness. But in the last 10-15 yrs they have improved tremendously. BTW, if you happen to lose 15hp, you will never notice it.

I would bet that only about 20% of owners use anything close the full output of their engines.:rolleyes:

[richtersand]

But a reaction to one point you made. You said you want it quieter so you don't have to wear ear plugs. Please reconsider this. The sound of the exhaust is almost unheard in my Coyote powered Mk4 when cruising in 5th at highway speeds. Regardless of what side pipes, cats, whatever, can't imagine it being much quieter. But the interior noise level in the open top car is still in the 90's dB range. I've monitored it several times use an app on my iPhone. Combination of engine sound, tires on the road, wind, traffic, you name it. These cars are loud not matter what. In that environment, you should wear some kind of ear protection and just make it part of your driving experience. Like buckling up the harness. Long term damage can result at those levels.

Noted, and thanks for the feedback on the ear plugs. I didn't think about the wind and other factors, but it makes sense now...