Will deleting my cats make the car louder?

 

Yep

 

Which cats? There are two sets of cats. But yes.

 

2 sets of cats?
those located after the exhaust manifold between upstream and downstream O2. My tuner suggested that I'd get rid of my cats because of my new BTR 220 cam but I don't want to have a loud car on cruising

 

One set of cats are on the X-pipe. They are not hooked up to anything. You can replace the X-pipe with a catless x-pipe, recommended, just a bit more noise. The two cats up stream are a bigger issue.

 

Circled all four of them in the first pic below.

Unless you're doing headers it's asinine to remove the main cats if you're keeping the OEM manifolds. Those exact same factory cats support 650hp with the Z06.

Even with headers, unless you want to smell like gasoline fumes when you get out of the car, you need to add bullet cats (second pic are mine). The BTR 220 is just large enough that the duration at idle will result in the smell.

I can tell you that with headers and bullet cats, when I fire the car.....even with the NPP exhaust set to "Tour" so the valves are closed....the neighborhood hears me. Once the engine settles down, it's much better but certainly louder than stock. When I have the NPP valves open, it's race car loud. Passing a sound station on track I was flagged for exceeding the sound limit of 103dB.



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Yes you can do it but why? IF I was at the point where the power gained would be the difference between 1st prize and endorsement deals or 1st loser with little to show for it but a bunch of bills, absolutely I would do it. Damn my hearing and discomfort. I can always learn sign language when I am deaf.

 

haha Jim I bet. And no I'm not fan of removing it for 2 reasons: in europe it's mandatory (we have yearly inspection) and I don't want to be louder. Yearly inspection I can trick them by swapping the orig parts of course but my real concern is the noise here

aklim, my tuner said my cam will lower the life expectancy of my cats and it would be better to remove them as they usually do. I asked him to retain them tho

 

With a stock cam on most cars, removing the cats won't be too noticeable at stoplights and garages.

I first installed catless downpipes on my M4 CSL and I noticed it had NO smell--just like the stock catted DPs.

The complete lack of smell after removing stock catted DPs on M4 CSL was due to secondary cats (not monitored) in the stock mid-pipes. After removing stock mid-pipes and installing a single 4.5" catless midpipe, the smell increased at the tailpipes--but not objectionable whatsoever. Definitely enough to smell like a traditional exhaust from the 60s, but not bothersome.

On the other hand, after installing a 235/252 GPI cam in the LS3 in my Chevy SS, the smell became unbearable--my clothes and skin smelled like gasoline after short drives.

When you install a cam
with more overlap (ie a cam the manufacturers could
never install because of emissions) you have to dial back the misfire monitor or else you will get a cel. That misfire monitor is accurate--large cams are LITERALLY misfiring at idle. The reason large overlap cams have poor idles is due to the misfiring. Alot of unburned fuel gets pushed right out the exhaust without igniting and helping the engine run. Even with a very accurate tune that I spent weeks on.

Depending on the size of your cam, the low rpm misfires can get bad enough to make your eyes water at idle and leave your passengers smelling like they've been bathing in gasoline.

And to answer your question, cats often have a side effect of muffling the exhaust as well as traditional mufflers. In my experience, cars can often (but not always) get QUITE a bit louder after removing stock cats (depending on how restrictive the stock units were to begin with)

 

Ok it makes sense. Notes for later, always push the motor hard

 

I have npp on my z06. removed oem primary cats added catless downpipes . oem mid pipe with resonators. loud on startup (cold start) close the valves neighbors are fine. no smell.

 

Add a cam with 240*+ of duration, overlap, plus headers, plus normally aspirated and you’ll hear it and smell it.

Comparing something with a stock cam and blower is apples and oranges.

 

I was just telling the o/p that it is louder on startup but app quiets it down. when I was catless misd pipe the smell was terrible. reinstalling the oem mid pipe cured the smell from now . when im on e85 it wont be an issue to be catless

 

The corn does smell good

 

OK. What am I missing here? I had a C4 that was modified to 420 RWHP. No precat or main cat. TPIS LT headers and Borla Stinger exhaust. Was it so noisy I couldn't hear myself think? Yes. Later on, I added the main cat so it made it tolerable. Tolerable, not pleasurable. I was so happy when my Borla came off and ripped itself off. Insurance paid for a new exhaust system so I got Corsa. Much better but still loud as hell.

In any iteration, even without the main cat, I really didn't seem to notice much smell, if any at all unless I was doing some work and idling it in the garage during winter with the garage door cracked open. What is this smell everyone seems to talk about? I drive forward, exhaust goes out the back. How do I smell that unless the car is parked and idling with me walking around? Maybe a little if it is in the garage and I fire it up and back out but when it is parked outside, I don't smell anything at all.

 

The cat lightup noise out the exhaust on startup with headers/no cats is awful. Basically 8 seconds or so of BLAAAAAH that echoes off your neighbors houses until it calms down. After that the car is obviously louder but not that bad. If anything I might think it's still a little too quiet at times...
The government stepped in and made HPtuners take out the ability to turn off the cat lightup, I've tried bandaids to do a similar effect but nothing really works

 

Back in the day when the cat system was inefficient or if you toasted the cat and can't afford a new one, I get it. Today, what does the cat really cost me? A couple HP at the top? If you are racing professionally, totally understandable. Today, what is the point of cutting it off? Besides impressing the boys, is the noise really meaningful in any quantifiable sense?

 

They occasionally melt if you track the car.

 

Fair point. Thanks. I did not realize they're that weak. I always assumed if you tuned it properly, it should not happen.