Fox Will 2 different mufflers on same car cause any issues

MrPerfect2

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91 vert GT - no engine mods - 2 front factory cats ( rear cats removed ) x pipe , OEM headers , car has 2 regular type looking mufflers ( I cant see any brand markings ) car sounds good like it is , but I want a bit louder . I have used flows 40s decades ago and remember they sounded good with 4 OEM cats and the H pipe ( but they did seem to pop a lot down shifting ) . I heard some spins 9000 on long tubes no cats and they sounded good . Can I just change one muffler to a flow or spin without causing the heads to have a lopsided amount of exhaust flow? My thoughts would be the X part of system would balance the pressures -
 
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MrPerfect2

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John Dirks Jr

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The cats are probably the most restrictive part. Although its really odd to have mis-matched mufflers, I don't think it would cause any functional problems with the engine. At least not with a stock engine that is exhausting through restrictive cats.
 
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Noobz347

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but I want a bit louder

I recommend building more motor and allowing the exhaust note to work itself out.

In the meantime, do a little research on "exhaust scavenging" and "tuned exhaust" systems.

Finally, if what you are trying to do doesn't somehow help to increase the performance and/or efficiency of the overall machine then it's urine in the breeze. The point [should] be to not end up with a cobbled together piece of gokart at the end of it all.
 

MrPerfect2

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I don’t have the $ to do engine mods - it’s my daily driver - cleaned engine bay , did plugs , wires , rotor / cap , coil , pvc , 327 gears - I want a bit more sound though and want to know if mismatched mufflers would cause any issues to engine functionality .
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General karthief

wonder how much it would cost to ship you a pair
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It would have to be an extreme difference in flow before you would notice. It also would likely differ in temperature, the more restrictive one would be hotter.
 

LILCBRA

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I don't see how it would affect the engine negatively in a huge way, but I think it will sound weird if one muffler is less restrictive (meaning louder) than the other. My suggestion is to replace them as a matched pair, I think you'll be happier with the result. And, as Noobz says, "The point [should] be to not end up with a cobbled together piece of gokart at the end of it all."
 

MrPerfect2

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I just read about exhaust scavenging. If I got the theory correct , It’s about back pressure and Venturi effects helping drawl more exhaust out of the heads . It’s coincidence because I was actually thinking this when I had the 2 cats removed and swapped the H for an X pipe . When I had the 2 extra cats and H , the car drove well and had smooth power delivery into the upper rpms. Now the car still drives well but feels as if a power band opens up around 2500 rpms (almost like about 2-3 psi of turbo boost.) I like that feature . Might be the X or the cat removal or combo of them . The car sounds pretty good the way it is ( like a 3 chamber flowmaster system with cats - I would prefer a 2 chamber sound ) it has 0 drone . If I switch out one muffler the scavenge process may be thrown off and I may loose the power band feel I now have . If I switch out both mufflers - they may disrupt the process as well and I may introduce the popping sound and drone noise ( both which I don’t want ) Safe bet would be to leave it the way it is and just not have it louder .
 

Noobz347

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It’s about back pressure and Venturi effects

The first part is incorrect but the Venturi effects are correct.

Creating "back pressure" is counter productive and not desirable. Getting the diameter and length correct so that each exhaust pulse helps to [pull] the next, is the overall goal.

Making changes between exhaust sides interrupts that pulse.
 

General karthief

wonder how much it would cost to ship you a pair
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There is a member here that is pretty much a header expert. (I'll try to find his write up), this is what I have gathered from his posts, let me say that he builds mostly race applications but it flows (see what I did?) over to the street.
Header design is more important than exhaust pipes and mufflers, when it comes to scavenging. That's to say the pipes and mufflers don't play a part but unless you are pushing 350 hp and up the exhaust is mostly just a path the exhaust follows.
Now before I catch flack from some of the more knowledgeable/experienced members here let me say you can hurt the performance of any engine by not sizing the exhaust properly, you also can hurt performance by using too large exhaust piping.
@geoklass
 

Noobz347

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There is a member here that is pretty much a header expert. (I'll try to find his write up), this is what I have gathered from his posts, let me say that he builds mostly race applications but it flows (see what I did?) over to the street.
Header design is more important than exhaust pipes and mufflers, when it comes to scavenging. That's to say the pipes and mufflers don't play a part but unless you are pushing 350 hp and up the exhaust is mostly just a path the exhaust follows.
Now before I catch flack from some of the more knowledgeable/experienced members here let me say you can hurt the performance of any engine by not sizing the exhaust properly, you also can hurt performance by using too large exhaust piping.
@geoklass


You are forgetting that Fox Mustangs use a tuned exhaust. Race applications do not compare well with street.
 

Noobz347

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General karthief

wonder how much it would cost to ship you a pair
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Ok, there is a certain amount of 'tuning' done by the factory on an exhaust system, some more than others, they did more 'tuning' to the exhaust of the 5.0 fox than they did to the more pedestrian focus.
All you have to do is look at the difference between the muffler design over the last say 25 years or so.
I figure mrperfect is not going to replace one of his mufflers with one off a toyota tercel. :jester:
 

General karthief

wonder how much it would cost to ship you a pair
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I think mrperfect could benefit from reading this, although it deals with mostly headers.
 

MrPerfect2

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I can see how 2 different pulse waves could be problematic ( I am a stereo guy and understand sub building ) I saw some spin tech 6000s that look good and sound good with no drone or popping - if I do anything I will do both mufflers
 
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