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How important is backpressure?

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Old Sep 11, 2008 | 04:17 PM
  #1  
mustangslayer86's Avatar
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From: Denton, Maryland
Car: '88 GTA / '93 Z28
Engine: L98(350) / LT1 (350)
Transmission: 700R4 / 4L60E
How important is backpressure?

Well I have a high flow cat waiting to go on where my gutted cat is (my uncle found me a free high flow cat, so I'll give it a shot) and my muffler really is making a weird sound like a loud screeching sound. It was a cheap muffler and looks to be poorly made... I've only had it since february... So I was wondering... what would happen if I left my gutted cat on there AND did a muffler delete? What will it feel like and how will it effect my driving?

Oh and last, but not least... HOW MUCH LOUDER? I'm really trying to stay away from the obnoxious truck loud.

MORE: the muffler I have on there was a $50 piece of junk that was supposed to be built exactly like a flowmaster.

Last edited by mustangslayer86; Sep 11, 2008 at 04:20 PM. Reason: Another question added.
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Old Sep 11, 2008 | 04:58 PM
  #2  
ghettosnowman's Avatar
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Car: 1988 Iroc-Z
Engine: 350
Transmission: 4L60E
Re: How important is backpressure?

If you lose the muffler....it will be loud. But not a good loud. What you're looking for is tone. If you want an idea of what it will be like without the muffler, start your car when you pull out the old cat. This will bypass the muffler and give you an idea of what you will get.

Last edited by ghettosnowman; Sep 11, 2008 at 05:03 PM.
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Old Sep 11, 2008 | 05:15 PM
  #3  
91 camaro racer's Avatar
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From: Fairfield, CA
Car: 91camaro rs,2014 silverado 5.3L
Engine: 5.7Lcarb,5.3L
Transmission: 700-r4, 6L80
Axle/Gears: strange 3.73's
Re: How important is backpressure?

Re: How important is backpressure?

here read this. great write-up about the subject, also a sticky on the top of the page...https://www.thirdgen.org/forums/exha...-you-ever.html
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Old Sep 11, 2008 | 06:55 PM
  #4  
mustangslayer86's Avatar
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Joined: Feb 2008
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From: Denton, Maryland
Car: '88 GTA / '93 Z28
Engine: L98(350) / LT1 (350)
Transmission: 700R4 / 4L60E
Re: How important is backpressure?

Well the first line answers my question. Unrestricted Flow = Unrestricted power, but I'd like to know how it feels not how it works.

I'll see if I can find a video of a car with open exhaust.

And look guys... If I need a new muffler I really need to try to get it for under $125. Is there many options or should I save more?
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Old Sep 11, 2008 | 07:11 PM
  #5  
91 camaro racer's Avatar
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From: Fairfield, CA
Car: 91camaro rs,2014 silverado 5.3L
Engine: 5.7Lcarb,5.3L
Transmission: 700-r4, 6L80
Axle/Gears: strange 3.73's
Re: How important is backpressure?

well right now i have headers and a y pipe. my low end kind of sucks. because having that short of exhaust moved my power range higher in the rpm scale. once i get my full exhaust i will have better low end. right now once it hits 3500 to 4000 rpm i can feel it pick up a little. hope that helps.
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Old Sep 11, 2008 | 07:20 PM
  #6  
mustangslayer86's Avatar
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From: Denton, Maryland
Car: '88 GTA / '93 Z28
Engine: L98(350) / LT1 (350)
Transmission: 700R4 / 4L60E
Re: How important is backpressure?

OK one more question for you... I have the stock pipes still on there... If I were to go looking for a muffler... what would the inlet, and outlet sizes be. (I don't know this one because my friend gave it to me)
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Old Sep 12, 2008 | 12:06 PM
  #7  
91 camaro racer's Avatar
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From: Fairfield, CA
Car: 91camaro rs,2014 silverado 5.3L
Engine: 5.7Lcarb,5.3L
Transmission: 700-r4, 6L80
Axle/Gears: strange 3.73's
Re: How important is backpressure?

stock size is either 2 1/4 or 2.5 cant really remember which one it is
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Old Sep 12, 2008 | 12:18 PM
  #8  
igotta355z28's Avatar
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From: Bedford Tx
Car: 1991 Z28 1LE
Engine: 370CID GenIII
Transmission: 4l60e
Axle/Gears: 4.33 Moser 9inch
Re: How important is backpressure?

here is a video of my IROC with hooker headers,ypipe cat delet and flowmaster catback...but the muffler was off so maybe this will help you on your sound quest....thats at idle from about 25ft away the sound was tryin to overpower my camaera mic. thats why i never reved up much....it sounds cool to me but is obnoxiously loud. Ive just been working on the car when its driveable ill take it to my buddies exhaust shop and have the flowmater muffler welded back on because i love that sound........
http://www.youtube.com/watch?v=x_IRJC7rbzY

Last edited by igotta355z28; Sep 12, 2008 at 01:53 PM.
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Old Sep 12, 2008 | 01:44 PM
  #9  
five7kid's Avatar
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From: Littleton, CO USA
Car: 82 Berlinetta/57 Bel Air
Engine: L92/LQ4 (both w/4" stroke)
Transmission: 4L80E/4L80E
Axle/Gears: 12B-3.73/9"-3.89
Originally Posted by mustangslayer86
OK one more question for you... I have the stock pipes still on there... If I were to go looking for a muffler... what would the inlet, and outlet sizes be. (I don't know this one because my friend gave it to me)
Originally Posted by 91 camaro racer
stock size is either 2 1/4 or 2.5 cant really remember which one it is
'86 TPI the stock I-pipe inlet to the muffler is 2-3/4". Tailpipes are 2-1/4".
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Old Sep 12, 2008 | 08:27 PM
  #10  
mustangslayer86's Avatar
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From: Denton, Maryland
Car: '88 GTA / '93 Z28
Engine: L98(350) / LT1 (350)
Transmission: 700R4 / 4L60E
Re: How important is backpressure?

Originally Posted by five7kid
'86 TPI the stock I-pipe inlet to the muffler is 2-3/4". Tailpipes are 2-1/4".

Thank you very much.
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Old Sep 12, 2008 | 09:35 PM
  #11  
mustangslayer86's Avatar
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Joined: Feb 2008
Posts: 151
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From: Denton, Maryland
Car: '88 GTA / '93 Z28
Engine: L98(350) / LT1 (350)
Transmission: 700R4 / 4L60E
Re: How important is backpressure?

I'm gonna make a new post for my next question because it has nothing to do with this topic. I might be able to find it in the past topics. I'll look. Thanks guys.
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Old Sep 13, 2008 | 05:35 PM
  #12  
zddp8868's Avatar
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Joined: Sep 2008
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From: South Jersey
Car: 1968 chevelle
Re: How important is backpressure?

will it be loud, yes. will it sound good, not if you have a stock motor. will you lose backpressure, yes. will that negatively effect the engines performance, no.

you arent losing enough backpressure to kill the scavenging effects of your engine because you are still keeping the most important part of the exhaust on: the pipes.
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