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What, if any, are the negative effects of gutting the 3rd cat, replacing the resonator with straight pipe and cutting both mufflers off of our 4.6 Birds?
About 7 years ago I wanted a loud and obnoxious exhaust and did the above "modifications" on mine and i'm wanting to tone it down now so I'm planning on adding a pair of Magnaflows back on but I'm just curious as to what is effected when removing these parts (good or bad)?
I'm guessing that there is a loss of back pressure which obviously decreases performance but what else?
 

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i'm told that whole backpressure thing is a load of hooey.

and really as long as your 2 forward cats are still in place for the downstream O2's, or even not if you eliminate those O2's with a tune; theirs no ill effects from opening up your exhaust. well save for more hydrocarbons in the atmosphere.

and the resonator just changes the tone by canceling some of the higher and lower frequencies for an even quieter, better sounding, and more restrictive exhaust system.

just slap some mufflers on the ends and call it a day.
 

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Discussion Starter #3
I will put mufflers on regardless, I was just curious if there were any other negative effects aside from the supposed loss of back pressure.
 

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I will put mufflers on regardless, I was just curious if there were any other negative effects aside from the supposed loss of back pressure.
Without smooth transitions and typically some sort of muffler/resonator/baffle/catalytic/etc, the exhaust will have excessive turbulence which will cause a minimal/mild loss of power usually you can hear the turbulence on a mufflerless/catless/both system by the popping sound on deceleration, that's the sound of exhaust pulses colliding against each other. Back pressure = Bad, loss of velocity/increased turbulence = bad.
 

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Back pressure is something that's hard to say is good or bad because it depends on your cams and timing and induction system.
Stock engine, some is good. It's designed for it. As you start to modify then it becomes something you're trying to reduce to boost volumetric efficiency.
 

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Someone else put this together but you can see the no muffler route was the worst in horsepower and loudest. No gain in either area as loud doesn't equal a good high power note.

The results in HP order:

1.Flowtech Warlock (open) 374.2 hp/ 333.1 tq
2.Bassani Real Street 373.7 hp/ 333.8 tq
3.Hooker Maxflow 373.5 hp/ 333 tq
4.Borla XS 373.3 hp/ 332.6 tq
5.Magnaflow 372.8 / 332.5 tq
6.MAC 372.3 hp / 331.5 tq
7.Flowtech Afterburner 372.3 hp/ 330.1 tq
8.Hooker Aerochamber 372.1 hp/ 330.4 tq
9.Bassani 372 hp/ 333.5 tq
10.Spintech 371.6 hp/ 332.2 tq
11.Edelbrock Performer RPM 370.9 hp / 331.3 tq
12.Borla XR1 370 hp/ 334 tq
13.Flowtech Terminator 369.5 hp / 331.3 tq
14.Dynomax Ultra Flo 369.4 / 333.2 tq
15.Flowmaster 369.4 hp / 331.8 tq
16.Flowtech Warlock 366.3 hp / 325.3 tq
17.No muffs 365.2 hp / 330.1 tq

Sound Off in Quietest to Loudest (Decibels):

1.Borla XS, 80db at idle, 90db at 2,000 rpm, 110db at WOT.
2.Hooker Maxflow, 80db at idle, 90db at 2,000 rpm, 120db at WOT.
3.Magnaflow, 82db at idle, 91 at 2,000 rpm, 114db at WOT.
4.Flowmaster, 82db at idle, 93 at 2,000 rpm, 115db at WOT.
5.Flowtech Warlock, 83db at idle, 92 at 2,000 rpm, 112db at WOT.
6.Dynomax UltraFlo, 83db at idle, 94 at 2,000 rpm, 113db at WOT.
7.Borla XR1, 83db at idle, 96db at 2,000 rpm, 118db at WOT.
8.Bassani Street, 83db at idle, 96db at 2,000 rpm, 120db at WOT.
9.Edelbrock RPM, 84db at idle, 93db at 2,000 rpm, 118db at WOT.
10.Bassani Real Street, 84db at idle, 96db at 2,000 rpm, MAX. (120+db).
11.Flowtech Afterburner, 86db at idle, 94db at 2,000 rpm, 115db at WOT.
12.Flowtech Terminator, 86db at idle, 94db at 2,000 rpm, 119db at WOT.
13.Hooker Aerochamber, 87db at idle, 94db at 2,000 rpm, 114db at WOT.
14.SpinTech, 87db at idle, 97db at 2,000 rpm, 116db at WOT.
15.MAC, 87db at idle, 98db at 2,000 rpm, 119db at WOT.
16.No Muffler, 91db at idle, 103db at 2,000 rpm, MAX. (120+db).
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I had clogged cats, and gutted all three of them, and removed the resonator, and cut the stock mufflers off. I straight piped the resonator, and left no mufflers on the car. Sounds great in my opinion. sounds nice at cursing speed, and if to lay into the throttle it sounds powerful. As for the back pressure, mine didn't idle right, and basically didn't work due to clogged cats. Now it runs perfect, and sound nice. I can post a video if you would like me to.
 

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I'm interested in hearing how it sounds cruising down the road inside. I've always read that they drone badly without the resonator and you have nothing at all so I'm curious
 

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I'm interested in hearing how it sounds cruising down the road inside. I've always read that they drone badly without the resonator and you have nothing at all so I'm curious
I will get you a video soon. My phone camera doesn't pic up audio well enough inside the car to hear it.

It does drone a lot if you constantly lay into the throttle (depends on how you drive it) but in mine I had the O2 holes without O2 sensors for a day. It was really loud, but I put in the O2 sensors, and sounds just fine to me. More of a personal opinion really. It does drone, so be fore warned.

Will get a video as soon as I get a better camera!
 

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I plan to upgrade the exhaust on my stock '95 Thunderbird LX 4.6.

Here are the main parts to my build plan.




Here is a link to the pipes:
http://www.mandrelexhaustsystems.com/servlet/the-116/92-dsh-97-THUNDERBIRD-EXHAUST-TUBING/Detail



Here is a link to a company that sells other components:
https://www.supercoupeperformance.com/



Below are some pics from their website.


Don't what to run the angled cats.:facepalm: So instead...
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Need four of these O2 sensor bungs:
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One of these to balance the banks, and provide a deeper tone:
[/URL][/IMG]



Better get one of these resonators to combat the drone:
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And two of these at 2 1/2" inlet center, and 2 1/2" outlet center:



I want to hear the V8, and this will provide quality sound, and some performance enhancement. Cost: including four new sensors, weld labor, and tax should hover south of one large.
 
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