update on cat removal (way to LOUD) and great fix.....

[1TONY1]

Background: Due to a hot cat burning the paint on the side sill I had removed the cats and replaced with straight 3" pipe. My exhaust was 3" with the stock cats reduced to half length and 3" Dynomax ultra flo race mufflers behind the cats in the side sills with 3" out the back....no muffler in the back.

The cat replacement 3" pipe caused the car to be a whole lot louder.....unbearable for me to drive everyday....maybe it was also the drone that was getting to me.

I replaced the 3" (cat replacement) pipe with Moroso race mufflers, with the Dynomax mufflers still on. This made my car as quiet if not quiter than before and the drone is gone. Inside the car the sound dropped a minimum of 3 to 4 decibels at different rpm's and part throttle acceleration. Yes it was so bad I bought a decibel meter to check before and after. The difference at two test points behind the car was 10 db. All tests were at the same spots, rpm, etc. They are 4" in diameter, 12" long body, 18" overall length. The stock cats were about 4 3/4" diameter and about the same length so they fit nicelyin the side sills. See them here:
http://www.moroso.com/catalog/categorydisplay.asp?catcode=35001
They also have 2.5" and 3.5" in/outs. Cheap easy fix at $90.00 for a pair. I have seen the flow in inches in the catalog....doesanybody know what stock or high flow cats flow in inches ?

 

[MES]

FYI I lost a significant amount of HP and TQ (dyno proven) with these mufflers over a straight 3" muffler. High flow cats will probably net you more HP, less noise, plus be EPA compliant.

 

[treynor]

I believe the garden-variety high-flow 3" cats flow 340-380 CFM, and the super-expensive ceramic-metal ones flow 520 CFM each.

 

[95Viper]

Tony, What do you mean by drone? I have a stock setup on a 95 and am close to replacing them with a 3", no cat setup from Northwood. I want to help fix the heat problems. I don't drive the car much and don't mind noise but I don't want to give my wife a headache. Thanks, Craig

 

[Bill/APEX Motorsports]

Tony, those mufflers are traditionally called "auger" mufflers, since they look like an auger used for digging post holes. The spiraling can really slow down the exhaust flow, so it's important that the central tube be large diameter. However, I haven't seen a central tube that was over 2". Do you know the diameter of the tube in the Morosos?
In any case, glad you like the outcome on your car! We looked into those a while ago and couldn't find any that met our flow needs.

 

[1TONY1]

Bill, I think the center tubes were 1.5". I am looking for the flow numbers that I saw and have requested the tests from Moroso.
Not in all cases....but for the most part more flow = more sound.....I was very unhappy with the loudness and for my sanity I had to do somthing asap, .the point was not to gain hp but to quiet the car without loosing hp from when the cats were on.. Who can do a flow test on my cat and one of these mufflers ? I will buy another one and have them tested.

Somebody give Craig a definition of drone: constant noise/rumbling/vibration that ****** me off ?

 

[1TONY1]

Thanks Mike, Look at my first post. I have the ultra flow 6" body, 3" in/out. Mine are in the side sills....where are yours ?
I was almost to the point of having to wear the Bose anr's.


Edit: You guys have me wondering now....I am going to build a flow device with an electric leaf blower using inches of water to see which flows better....the modded stock cat or the Moroso muffler. At that time I would like to compare a high flow cat and could do other mufflers if anyone needed a comparison

 

[99 R/T 10]

Hey Tony,
There is a difference between the 3" race muffler as you stated you had, and the 6" Ultra flows. I have mine in the back of the side sill and it is a very tight fit. This is the only muffler I have(one on each side) on the car. I cut the cats and put straight 3" pipe in place of the cats. I love the sound, perfect IMHO.

Mike

 

[opnwide]

Craig,
regarding your '95, I would not go catless with those mufflers. I have Roe hi-flows and Dynomax 3" bullet (race) mufflers, and my wife HATES it with the ragtop on. Top off, well...its bearable for her.

If you are not going to go with headers, I would cut the original exhaust at the back side of the cat and weld 2 1/2" race mufflers on it. I only gained 13hp with the 3" system from the factory 2 1/4" header outlet. NOT worth it. If you were close to Austin, I'd trade you.

By the way, our cars were probably made on the same day!

 

[1TONY1]

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by 96 R/T 10:
Hey Tony,
There is a difference between the 3" race muffler as you stated you had, and the 6" Ultra flows. I have mine in the back of the side sill and it is a very tight fit. This is the only muffler I have(one on each side) on the car. I cut the cats and put straight 3" pipe in place of the cats. I love the sound, perfect IMHO.

Mike

<HR></BLOCKQUOTE>

Mike, The 3" was referencing the in/out not the body, the body is 6".This is what I had: factory cat cut in half (Hennessey) and behind the cats the Dynomax 6" round with 3" in/out which looks like:

Now I have the Moroso where the cat was.....I STILL have the Dynomax behind the Moroso mufflers = 2 mufflers on each side.
What I did was replace the cats with straight 3" so mine was just like yours......it was to loud for me. 80 mph and I could not talk in a normal voice to the passenger. I loved the way it sounded with the modded cats and Dynomax. I do have decibel test on both systems....I wish I would have done tests with the cats on but I didn't expect the great increase in sound. After cat removal about 10 feet directly behind the car it was at 102db now: 92db, 60mph in 4,5,6th gear was 90db now 87db, idle in car was 82db now 80db, 4th gear @ 40mph was 89db now 83db. I will take some measurements on a stock exhaust Viper, mine is still a lot louder than stock. Here is the db lesson of the day .......Here is a chart showing some db comparisons:

Also:
Noise Source Decibel Level Noise Effect
Jet takeoff (25 M) 150 Eardrum rupture
Aircraft Carrier Deck 140 Earphones at high level
Jet takeoff (100 M) 130
Thunderclap, Live Rock Music, Chain Saw 120 Human Pain Threshold
Steel Mill, Riveting, auto horn at 1 M 110
Jet takeoff (305 M), Outboard motor, power lawn mower, motorcycle, farm tractor, jackhammer, garbage truck 100 Serious hearing damage (8 hrs)
Busy urban street, diesel truck, food blender 90 Hearing damage (8 hrs)
Garbage disposal, dishwasher, average factory, freight train (15 M) 80 Possible Hearing damage
Freeway Traffic at 15 M, vacuum cleaner 70 Annoying
Conversation in restaurant, office, background music 60
Quiet suburb, conversation at home 50 Quiet
Library 40
Quiet rural area 30
Whisper, rustling leaves 20 Very Quiet
Breathing 10
0 Threshold of hearing

 

[MES]

FYI copied from an old post using Corsa 3" and R/T high flow cats

Here are some readings taken in 2nd gear from inside the car
Idle 74 db
2000 80 db
2500 79 db
3000 76 db
3500 77 db
WOT 93 db
coast down while in gear 84 db max around 2500
Lightly accelerating through the gears averaged 80-84db
Idle outside the car with the meter sitting on the rear deck 84db
Idle outside the car about 5 feet behind the tail pipes 88db

 

[99 R/T 10]

Tony,
I have the TNT 3"(instead of the TNT muffler I went with 6" Ultra flow from Dynomax), no cats, and for me the drone is not bad at all. Of course I do have the option to take the top off. You may want to replace the race muffle with the 6".

Mike