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View Full Version : Cutting out Cat, Noise difference...?



89ShelbyGuy
06-02-2008, 04:08 PM
Hey guys, i have put on a 2.5 inch exhaust on my daytona..i have a 2.5in d/p into the catty then into a glass pack tubular muffler, then out the side...i plan on getting a exhaust system from one of the vendors (anyone know who's is better or about the same?!?!) and i would like to cut out the cat and run it staight to the glass pack muffler, then out the rear...i would like to know how much louder it would be...if any, it would be...cause its preatty loud as it is right now....Thanks!

turbovanmanČ
06-02-2008, 04:44 PM
Yes, it will be louder. How much, impossible to say as some cats are restrictive, some are not as much.

Speedeuphoria
06-02-2008, 05:46 PM
some will depend on how old/cloged the cat is currently

BadAssPerformance
06-02-2008, 06:33 PM
Cats block a lotta noise. I'd run 3" from the DP out the back and a larger oval muffler like the Dynomax Race Magnum oval if you care about performance and sound :thumb: Have you heard my Shadow?

2.216VTurbo
06-02-2008, 09:57 PM
Don't cheat yourself on the pipe that runs out back, make sure the sound pulses get out from under the car. That last couple inches can make all the difference. On the exhaust that is;) Zip it Gazers:p

Mopar318
06-02-2008, 10:01 PM
Im a pretty big fan of side dumps. Have had them on all my cars. Im building a 3" side dump for my Daytona here soon.

2.216VTurbo
06-02-2008, 10:13 PM
Im a pretty big fan of side dumps. Have had them on all my cars. Im building a 3" side dump for my Daytona here soon.

Yeah, but you already admitted you're 20;) What works at 20 is not so fun at 40... I think a portion of my hearing loss is due to 65K miles worth of droning in my Shelby Lancer:o That ringing in your ears after a 200 mile day in the car, that's permanant hearing loss. Once the cillia in you middle ears is 'mowed down' by too much sound pressure, they don't ever get back up again.

Mopar318
06-02-2008, 11:17 PM
Yeah, but you already admitted you're 20;) What works at 20 is not so fun at 40... I think a portion of my hearing loss is due to 65K miles worth of droning in my Shelby Lancer:o That ringing in your ears after a 200 mile day in the car, that's permanant hearing loss. Once the cillia in you middle ears is 'mowed down' by too much sound pressure, they don't ever get back up again.

Actually side dumps seem to have less drone at high way speeds, at least in my experience. I usually run a packed muffler with no cat, then dump it behind the passenger door. Maybe Ill just run a cutout with a side dump on the Daytona for a while to see if its going to be too loud or not.

Of course for the passenger, its usually a different story.:lol: My girlfreinds have always loved the side dumps.:thumb:

GLHNSLHT2
06-02-2008, 11:43 PM
I have a side exit straight pipe on my ShelbyZ. It's ok inside the car. Just a deep burble at idle and an ok roar at WOT. Highway cruise you can barely hear it. That being said that's IN THE CAR. Outside the car while it's not deafening or irratatingly loud it does attract attention. I'm tired of romping on it and thinking "are the cops gonna hear me"? am I gonna get a ticket? I must be getting old at 32 because I want something stealthy. Course I just put 3" straight pipe on my 2.2 auto new yorker out the rear because I couldn't find a muffler I like yet. Same thing, quiet in the car but loud as hell at WOT outside the car. Even shoots flames on decel with the stock ECU.

Now when my GLH was 2.5" with a cat it was nice sounding although still picked up spool with the cat removed.

I'm at a crossroads here as well. Should I get a high-flow 3" cat for noise? Will it be enough? Will it kill spool?

Tom if I were you I'd leave the cat and get rid of the muffler :)

GLHNSLHT2
06-02-2008, 11:43 PM
I have a side exit straight pipe on my ShelbyZ. It's ok inside the car. Just a deep burble at idle and an ok roar at WOT. Highway cruise you can barely hear it. That being said that's IN THE CAR. Outside the car while it's not deafening or irratatingly loud it does attract attention. I'm tired of romping on it and thinking "are the cops gonna hear me"? am I gonna get a ticket? I must be getting old at 32 because I want something stealthy. Course I just put 3" straight pipe on my 2.2 auto new yorker out the rear because I couldn't find a muffler I like yet. Same thing, quiet in the car but loud as hell at WOT outside the car. Even shoots flames on decel with the stock ECU.

Now when my GLH was 2.5" with a cat it was nice sounding although still picked up spool with the cat removed.

I'm at a crossroads here as well. Should I get a high-flow 3" cat for noise? Will it be enough? Will it kill spool?

Tom if I were you I'd leave the cat and get rid of the muffler :)

The Pope
06-03-2008, 01:23 AM
The NY also has the .63 housing too and a stock cam. Smaller exhaust makes extra noise and so does a larger cam. My wagon with just a cat and a stock turbo with a bigger cam is a lot more noisy, with 3"

turbovanmanČ
06-03-2008, 01:04 PM
Yep, TIII turbo, 3 inch system, tried a side dump with no muffler or cat, :wow1: I couldn't even hear myself talk, :eyebrows:

The turbo size affects how quiet/loud it is, a mitsu with an open exhaust is fairly quiet, just raspy.

GLHNSLHT2
06-03-2008, 07:39 PM
The Pope thinks my .63 housing makes the car quieter Simon.

shadow88
06-03-2008, 09:21 PM
Yeah, but you already admitted you're 20;) What works at 20 is not so fun at 40... I think a portion of my hearing loss is due to 65K miles worth of droning in my Shelby Lancer:o That ringing in your ears after a 200 mile day in the car, that's permanant hearing loss. Once the cillia in you middle ears is 'mowed down' by too much sound pressure, they don't ever get back up again.

WHAT????

Oh, I'm just kidding. The additional popping on decel is a nice touch too when going cat-free. I like being quiet enough not to raise any eyebrows. I run cat and muffled 2.5" rear exit.

turbovanmanČ
06-03-2008, 11:24 PM
The Pope thinks my .63 housing makes the car quieter Simon.

Really, thats kinda azz backwards but ok, :confused:

Spraynlog
06-04-2008, 09:02 AM
Hey guys, i have put on a 2.5 inch exhaust on my daytona..i have a 2.5in d/p into the catty then into a glass pack tubular muffler, then out the side...i plan on getting a exhaust system from one of the vendors (anyone know who's is better or about the same?!?!) and i would like to cut out the cat and run it staight to the glass pack muffler, then out the rear...i would like to know how much louder it would be...if any, it would be...cause its preatty loud as it is right now....Thanks!
If you are running a stock cat, and you cut it out, it will be a lot louder. I recently tried running a glasspack off my 2 1/2" downpipe, and it was pretty much unbearable. You can read what I did in my post about the Edelbrock SDT muffler.:eyebrows:

MiniMopar
06-04-2008, 10:34 AM
Yeah, exhaust drone varies depending on your setup: eg. which SV/DP you have, where your exit is, what size pipe your have, maybe even the type of pipe...I dunno. I like to read the various muffler threads and all I can say is there are lots of different things to try and it seems like everyone has a different experience.

All that said, yeah removing the cat will make it louder for sure. I put a 3" system on the CSX a few years ago and it still has no cat. Even with two mufflers, it's louder than the Daytona with one straight-through muffler and a high performance cat from Dynomax. When I ran the Daytona briefly with just a muffler, it was VERY loud. I don't mind somewhat loud exhaust, but a lot of highway drone drives me nuts and I also don't want to get on the neighbor's bad side too much.

When I got my CSX in '98, the exhaust was old school: stock DP and cat with 2.25" cat-back and no muffler. It was fine at idle, but loud while driving.

turbovanmanČ
06-04-2008, 01:37 PM
I hate drone, it was ok when I didn't have to commute on the highway but when I moved, argg. The cat definately cut that out-but you could feel the power loss so now I have a extremely high flowing cat and will be trying a new muffler setup soon. :o

TurboSedan
10-07-2008, 11:03 PM
bumping an old thread here but i just got the 3" exhaust installed on my Spirit R/T and thought i would add my .02 rather than start a new thread.

previously my exhaust system consisted of the stock pipes, however i had a test pipe welded in where the cat was and no muffler at all. the pipe actually ended right before where the muffler was (just after rear tire). it was very loud but i could still drive it around that way. it wasn't loud enough that i got any trouble from the cops or any noise complaints. the only time it was really too loud was when i floored it and let the RPM really get up there which was hardly ever.

the car is REALLY quiet now. i think it's maybe just a little louder (deeper tone) than a completely stock exhaust system. mine consists of the 3" mandrel bent aluminized system from FWDP, along with a 3" Magnaflow cat and a round 3" Dynomax Ultraflo muffler and a turn down tip. the only real reason i decided to get the cat is because i wanted the car to be very quiet (stealthy). the exhaust shop put the turn down on, which i wasn't expecting them to do but i'm actually glad they did because you can't even tell the car has a larger exhaust system just by looking at the rear of the car.

my brother has exactly the same system on his Spirit R/T except he has a test pipe in place of the cat and the exhaust tip goes straight out. mine is definitely quieter than his and it is obvious whether the car is idling but especially when driving. he has the same 3" system from FWDP, exact same muffler as well, the only difference is the cat and tip. i would think that the turn-down would make mine a little louder if anything.

i'm definitely glad i bought the cat! now that i know they cut out so much noise i will be getting one for the CSX as well.

my R/T definitely feels a little quicker now...the first time i floored it i could tell it pulled harder than it ever had before. i didn't think i would notice much difference since i am only at about ~9psi and the system that was on there was simply straight pipe with no muffler or cat.

--------------------------------
Joshua Mitchell
'91 Dodge SPiRiT R/T
'87 Shelby CSX #667
'98 Buick Regal GS

thrashercharged
10-08-2008, 07:42 AM
>my R/T definitely feels a little quicker now...the first time i floored it i could tell it pulled harder than it ever had before. i didn't think i would notice much difference since i am only at about ~9psi and the system that was on there was simply straight pipe with no muffler or cat.

Anyone have any theories as to why the car would be quicker with the addition of a cat and muffler? My understanding from reading the post is that this is the same exhaust system, turbo, same boost, etc. just the addition of a muffler and cat, so there has to be more restriction. Why would the engine be making more power, especially being a turbo car?

JuXsA
10-08-2008, 10:25 AM
You can also put some sound deadening in your trunk floor and that will help a lot. I plan on doing that in the next few months.

TurboSedan
10-08-2008, 07:32 PM
it's not the same exhaust system. i went from the factory sized pipe to much larger 3" mandrel bent pipe.

------------------------------
Joshua Mitchell
'91 Dodge SPiRiT R/T
'87 Shelby CSX #667
'98 Buick Regal GS

turbovanmanČ
10-08-2008, 08:18 PM
Anyone have any theories as to why the car would be quicker with the addition of a cat and muffler? My understanding from reading the post is that this is the same exhaust system, turbo, same boost, etc. just the addition of a muffler and cat, so there has to be more restriction. Why would the engine be making more power, especially being a turbo car?


Why? Less backpressure than stock and being a turbo car, that is good, and larger pipes equals more flow than the stock system. :thumb:

BadAssPerformance
10-08-2008, 09:39 PM
Anyone have any theories as to why the car would be quicker with the addition of a cat and muffler? My understanding from reading the post is that this is the same exhaust system, turbo, same boost, etc. just the addition of a muffler and cat, so there has to be more restriction. Why would the engine be making more power, especially being a turbo car?

more restriction = more backpressure = more torque and throttle response off the line, but less overall hp at WOT

thrashercharged
10-09-2008, 12:57 AM
Anyone have any theories as to why the car would be quicker with the addition of a cat and muffler? My understanding from reading the post is that this is the same exhaust system, turbo, same boost, etc. just the addition of a muffler and cat, so there has to be more restriction. Why would the engine be making more power, especially being a turbo car?


it's not the same exhaust system. i went from the factory sized pipe to much larger 3" mandrel bent pipe.

Ok - that explains it. I misread the post (my fault - just reading it too quickly and not paying attention). I thought you had the same exhaust system and added the cat and muffler so it didn't make sense. I didn't realize you went from a factory setup with no cat and muffler to a 3" mandrel with cat and muffler.

I believe the stock pipes are 2.5" downpipe into 2.25" pipes with 2 90 deg mandrel bends, then over the axle with 2" or 2 1/8" pipe? It's interesting to know that a complete 3" mandrel with cat and muffler will outflow the stock system w/o cat and muffler.


more restriction = more backpressure = more torque and throttle response off the line, but less overall hp at WOT

In my experience I haven't seen this to be completely the case on a turbo car, except for maybe initially before the turbo spools while the engine is operating under normally aspirated conditions. But more restriction always increases turbo lag, so it's probably debatable whether some restriction does a turbo car any good. Increased restriction might gain some torque on initial take off before the turbo is spooled, but it'll take a bit longer to spool too, so the trade off may not be worth it.

I agree that increased restriction always equals less overall HP at WOT, especially on a turbo car.

Not trying to be picky, but just so someone doesn't get the wrong understanding, I'd like to clarify that more restriction = more backpressure = more torque isn't exactly true. More restriction does sometimes make more torque at a specific RPM, but the reason increased restriction can sometimes produce more torque on a normally aspirated engine (at a certain RPM) is not because of the increased backpressure, but because of the tuning effects (cylinder scavenging) that increased restriction can sometimes cause.

The point at which a pipe ends into open air (i.e. the length of the pipe) can have a pronounced scavenging effect on the cylinder. This is especially effective on 2-cycle engines and why different exhaust pipes can have such drastic effects on 2-cycle power, and why open header race engines vary the size, length, placement etc. of their pipes and collectors, all to tune for max efficiency at a particular RPM.

Pipe diameter also has a big effect on tuning, because as the exhaust gases travel away from the combustion chamber, they start cooling drastically and start decreasing in volume, so if the pipe remains too large, the velocity slows down. Decreasing pipe size will help maintain velocity and affect scavenging. This is a big benefit to OEMs because this allows them to tune their exhausts and still decrease the pipe size as they get toward the back of the car saving weight, cost, reducing sound levels, and making it easier to bend over the axle as well.

Adding a cat or muffler, or going with smaller pipes often does increase torque at lower RPMs, but it's due to this tuning effect, not because of the increased restriction or backpressure. The increased restriction and backpressure is often associated with increased torque but it's really a (unwanted) side effect that's a necessary evil. If one could, you'd try to achieve the same tuning effect without that unwanted side effect of increased backpressure, but that's not easily done, perhaps impossible.

BadAssPerformance
10-09-2008, 01:34 AM
^^^ agreed on all of the above, plus good info Thrasher :thumb:

factory exhaust on most turbo mopars is 1-7/8" over the axle :eek:

and yes, for a turbo car at WOT HP, the bigger the better :D

3" seems to work nicely for most 4cyl turbo cars even with larger turbos, on my shadow, I get the same mph with open downpipe or full 3" which just means the restriction is elsewhere...

Tony Hanna
10-09-2008, 02:03 AM
In my experience, all other things equal, a quieter car seems to "feel" faster. Running my old Daytona with an open downpipe vs. a full 2.5" manderal bent exhaust w/muffler was a really good example of this for me. I know the car should have been faster with the open DP but it didn't seem that way. It's gotta be a psychological thing... The extra noise diverts some of your attention away from how hard the car is pulling or something goofy like that. I don't know if that makes sense to anybody else, but it's something I've noticed.

amcpacer
10-13-2008, 01:18 AM
I just installed a 3 inch mandrel bent system with a 3" straight through FloPro muffler. I installed a 3" high flow cat converter and am sure glad I did because the car is so much quieter with it. The cat eliminated the droning that I had when the system only had a muffler and 3 inch pipes. I did not feel any loss of power but my car is only at 12 psi of boost right now. Perhaps a cat only hurts performance when running super high boost.

89boostedminivan
10-13-2008, 08:10 AM
i just removed mine the other day, 2.5" DP into 3" then into a glasspack then exits out the pass side under the slider door, gonna go back in a week or so and get a 3" DP but as it is now it sounds like a diesel truck,loL! its def louder but id say mainly in lower rpm's is were its the most noticeable. acceleration has greatly improved and thats with 18psi of boost