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Exhaust help

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Old Aug 2, 2025 | 03:17 PM
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Exhaust help

I have a 97 f250 with the 5.8. After 27 years my exhaust is finally about to let go, as it's holding on by only one hanger now. I don't care for replacing it with OEM parts so I wanted help on what I should do for an exhaust.

My plan is to remove the cat, and everything else behind it. I'm going to buy a cat delete flange, put a flowmaster on, and just have it exit the passenger side Behind the door.

I've heard that the diameter of the exhaust is what affects the back pressure, is this correct? What diameter should my exhaust be? I have the "dual" style exhaust, where it becomes two 1.5" diameter pipes after the muffler. At the cat, the pipe is 2", so should my new exhaust be 2"?

also, what would be a good flowmaster muffler to use? I've heard the super 44 is a good choice but I'm not sure what to pick. I don't want it to be like open headers, but I would like some good noise.
 
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Old Aug 2, 2025 | 04:36 PM
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Is it a single 2" going into the cat? Or are there 2 of those?
 
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Old Aug 2, 2025 | 04:38 PM
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Originally Posted by jas88
Is it a single 2" going into the cat? Or are there 2 of those?
it's two 1.5" and they merge into one. It's a rounded rectangle shape. Then the rectangle goes into the cat
 
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Old Aug 3, 2025 | 08:02 AM
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If you are merging those into one muffler, then I think it should be 2.5" or 3". I did the same on my 460 and mine is 3".
 
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Old Aug 3, 2025 | 09:51 AM
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Originally Posted by jas88
If you are merging those into one muffler, then I think it should be 2.5" or 3". I did the same on my 460 and mine is 3".
Why? Wouldn't that affect the back pressure? The two pipes merge into one before they enter the cat and it looks like it's about a 2 inch diameter pipe
 
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Old Aug 3, 2025 | 11:10 AM
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Based on your original post, I'm assuming you have a dual exit system. Not the same as a true dual system.

I wouldn't worry about chasing this, "back pressure" you want exhaust velocity, not restriction.
 
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Old Aug 3, 2025 | 11:34 AM
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Originally Posted by Junktownbill99
Based on your original post, I'm assuming you have a dual exit system. Not the same as a true dual system.

I wouldn't worry about chasing this, "back pressure" you want exhaust velocity, not restriction.
Yeah, that's right. I didn't know a good way to explain what style I had but I knew it wasn't true dual. So why does back pressure not matter on this style? And would exit velocity just mean a bigger exhaust that allows more exist fumes to escape?
 
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Old Aug 3, 2025 | 11:42 AM
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Originally Posted by Jsouz50
Yeah, that's right. I didn't know a good way to explain what style I had but I knew it wasn't true dual. So why does back pressure not matter on this style? And would exit velocity just mean a bigger exhaust that allows more exist fumes to escape?
"Back pressure" doesn't really mean anything, you don't want your pistons to be fighting the exhaust gas.

There's a bit of math to this, but in short: bigger ≠ better.

Bigger pipes will flow better at higher rpms, smaller pipes keep the velocity up at lower rpms, useful in a truck. Hotter gasses move faster. Bigger pipes radiate more heat, and let the exhaust expand more, both of which cool it down. 2.5" is probably a solid choice, do some research though.
 
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