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97F-3504X4PSD
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120 Posts
Discussion Starter #1
:usflag I keep reading the threads concerning 7.3l MPG. Someone always mentions staying under 2000 RPM. Why? What is the engine doing different above 2000? Just wondering.:thanks:
 

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Senior Member
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862 Posts
It's fueling more over 2K RPM's.

Every single engine gas or diesel has a specific RPM range that is optimal for fuel mileage.
 

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Diesel Enthusiast
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234 Posts
Torque curve would be my guess, but I don't exactly have a degree in this or anything.
 

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TDG Mafia Member # 70
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426 Posts
how fast are you all going at 2000 rpms? i am going 65 mph.

the reason i ask, is because i dont know what rear is in my truck. its not on the door frame nor the metal labels on the diff cover.
 

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Senior Member
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112 Posts
Allout0606 you have 3.73 ratio at that speed.
 

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Hotsauce2138
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496 Posts
i go 70mph @ 2000rpm
 

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Riding solow on the Hog
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TDG Mafia Member # 37
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I'll make that a 3rd. At 2000 rpm I am running 70 mph which is plenty fast when pullin my 5'er and it is where I get the best fuel economy on the highway. If I go over 2000 rpm to say around 2200 rom I'll lose about 2mpg in economy. Gene :mafia
 

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Member
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102 Posts
I run 65 @ 2000 rpm also (3.73). I try to keep it around that speed, but it's pretty difficult sometimes in MI, everybody wizzes by like you're standing still. Everybody running 70 @ 2000 has 3.55 gears. Kinda wish I had that ratio, but I could always swap them later.
 

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Hotsauce2138
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496 Posts
well what if we got bigger tires and a leveling kit doesnt that have something to do with higher speeds @ lower rpms?
 

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Senior Member
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862 Posts
HotSauce2138 said:
well what if we got bigger tires and a leveling kit doesnt that have something to do with higher speeds @ lower rpms?
Any mileage gains you get from lowering the RPM's that way are completely lost due to the larger rotating mass and the increased wind resistance.
 

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Mod Friendly Title
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My F-250 with 3.73 gears and oversized 285/75/16 tires is running 72 MPH on GPS at 2000 RPM. The speedo says it's doing 68-69 mph.
 

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TDG Mafia Member # 37
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901 Posts
I have 3.73 gears and my speedo indicates 70 mph at 2000 rpm. But I have found that my speedo is off by about 2 mph so i guess I'm actually going 68 at 2000 rpm. Gene :mafia
 

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97F-3504X4PSD
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120 Posts
Discussion Starter #14
I am going 60 MPH @ 2000 RPM. Jack your truck up. Put your xfer case in N. Mark your tire on the side wall and your drive shaft. Rotate the tire one revolution. Count the revolutions the shaft did. This will tell you your gear ratio.
 
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