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1997 GMC Safari SLX - AWD
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Discussion Starter · #1 ·
I have a bit of a head scratcher here.

I have always wanted a tad more sound from my vehicles. So when I bought my Safari months ago, I thought about the muffler right away haha. I don't want anything TOO loud (I had a Thrush 2 chamber 17651 on my Jeep 4.0, a copy of the flowmaster 40, and it was too much haha), so I thought it would be nice to get something like a Flowmaster 50 Series. It is shorter and lighter than that stock lead weight under there, so for offroad, a bit better too!

My question is as follows.... I know that the factory muffler goes from 3inches, to a 2.5 inch tail pipe, which I assume is for back pressure (?). I have read on here that it would be stupid to run a full 3 inch exhaust, as you would lose torque.... the Jeep XJ I owned was the same concept.

So here is the headscratcher: Would you run:

1. A 3" inlet / 3"outlet muffler, with a 3" --> 2.5" step down after the muffler

OR

2
. A 3" --> 2.5" step down on the pipe in front of the muffler, and then run a 2.5" / 2.5" muffler?


I am fairly certain each one gives a different result due to muffler volume, gasses going in/out, and back pressures.... or am I nuts, and it's a case of "6 of one, half dozen of the other"?

Anyone who has done a flowmaster or similar welded performance muffler... which route did you take?

Thanks !
 

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1998 LS AWD Forest Green metallic
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964 Posts
I have a bit of a head scratcher here.

I have always wanted a tad more sound from my vehicles. So when I bought my Safari months ago, I thought about the muffler right away haha. I don't want anything TOO loud (I had a Thrush 2 chamber 17651 on my Jeep 4.0, a copy of the flowmaster 40, and it was too much haha), so I thought it would be nice to get something like a Flowmaster 50 Series. It is shorter and lighter than that stock lead weight under there, so for offroad, a bit better too!

My question is as follows.... I know that the factory muffler goes from 3inches, to a 2.5 inch tail pipe, which I assume is for back pressure (?). I have read on here that it would be stupid to run a full 3 inch exhaust, as you would lose torque.... the Jeep XJ I owned was the same concept.

So here is the headscratcher: Would you run:

1. A 3" inlet / 3"outlet muffler, with a 3" --> 2.5" step down after the muffler

OR

2
. A 3" --> 2.5" step down on the pipe in front of the muffler, and then run a 2.5" / 2.5" muffler?


I am fairly certain each one gives a different result due to muffler volume, gasses going in/out, and back pressures.... or am I nuts, and it's a case of "6 of one, half dozen of the other"?

Anyone who has done a flowmaster or similar welded performance muffler... which route did you take?

Thanks !
I have never experimented with mufflers like that. In fact, I have had very few vehicles other than small imports, and they were often rally cars used in competition.
If it were mine, I would buy both adapters and do a trial in both configurations.
Rod J
Issaquah, Wa
 

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I replaced the pipe to a 2.5 inch and used a dynomax muffler. Originally had a thrush forever.

For yours a reducer after the 3 inch muffler is going to be as close to a factory set up as you can get.
 

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1997 GMC Safari SLX - AWD
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29 Posts
Discussion Starter · #4 ·
Thanks for the input folks! Alright, so I suppose get the 3" muffler, and then drop down to the tail pipe section. The reason I was confused is that the OEM boat anchor muffler has the 3" inlet and the 2.5" outlet.... so I was curious where the restriction happens. Just on the outlet, or somewhere internally.
 

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01 Astro RWD Cargo, 97 AWD Mark III
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2,021 Posts
As long as you are rebuilding the exhaust.
Walker 50418 Y pipe/ Catalytic converter with smoother bends for better exhaust flow.
 
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