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Not necessarily. I would think that pipes that are too large will decrease milage but not always larger = worse.
 

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Discussion Starter #5
the reason i ask is becuase im thinking of upgrading either my front half of my exhuast from 2" to 2.25" or just getting all new exhuast which would prolly be 2.25"

would an .25" really hurt me than? Am i better off with the old stock set up? id like to keep the great gass mileage i get...if i can. -TJ
 

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13's or Mildly Broken
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I ran 2.5" true dual on my 96 NPI 4.6 and still got 24-25mpg with it on the highway and never felt any difference in performance.

-Melon
 

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IMO, over 2.5" duals is where you would start to lose fuel economy....i routinely get 25-27mpg on the highway with 2.5" duals from the stock manifolds and high-flow cats.....i can still manage low-16s in the city if I keep my foot out of it
 

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Exhaust back pressure is a crutch. If you do a good job on the exhaust system, you don't need back pressure. Most engines make more low end torque from long tube headers.

Yes, a loss in low rpm power would be the major reason for lost mpg.

Yes some. But it's not the whole equation, and factory cams generally have very mild amount of overlap anyway.
the 4.6 has none. If you want to put a degree figure on it, it's -23.
 
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