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Discussion Starter #1
So, I've been noticing that I get right about 20 mpg on the highway. Mine is a 2010 R/T 6-speed, "unknown" mods (might have a tune, don't know), 3.92's, a K&N drop-in filter (had a Mopar CAI before I got it but the dealer pulled it to smog it - which is why I think it might have a tune), and currently has a Magnaflow Competition series cat-back. No other mods that would affect mileage. Traffic around here on the freeway flows at 75-80, so I'm wondering if it's just the higher speeds or maybe I need plugs/have another problem/etc. Car has 46K miles.

Any (helpful) ideas?
 

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2011 392 SRT, 2010 R/T Classic, 2019 R/T Plus, 2016 SXT Plus
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I have a 2010 R/T Classic Auto with a Magnaflow Competition, CAI, 93 CAI tune, and get similar.

I think my 2011 392 gets better gas mileage because it doesn't have to work as hard.
 

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Try cruising at 70mph with the cruise on.

It's the higher speeds.
I read before that every 5mph over 55 you get about 10% worse MPG.
So driving at 80mph you get about 25% worse MPG.
 

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So, I've been noticing that I get right about 20 mpg on the highway. Mine is a 2010 R/T 6-speed, "unknown" mods (might have a tune, don't know), 3.92's, a K&N drop-in filter (had a Mopar CAI before I got it but the dealer pulled it to smog it - which is why I think it might have a tune), and currently has a Magnaflow Competition series cat-back. No other mods that would affect mileage. Traffic around here on the freeway flows at 75-80, so I'm wondering if it's just the higher speeds or maybe I need plugs/have another problem/etc. Car has 46K miles.

Any (helpful) ideas?
My 2012 R/T 6m gets about 24 combined with a custom hemifever tune and Blastin' Bobs Magnaflow axle back exhaust, no other performance mods. I think that's pretty good for a hi-performance V8, besides, I didn't buy a Challenger for it's fuel economy, did you? >:)
 

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Discussion Starter #5
My 2012 R/T 6m gets about 24 combined with a custom hemifever tune and Blastin' Bobs Magnaflow axle back exhaust, no other performance mods. I think that's pretty good for a hi-performance V8, besides, I didn't buy a Challenger for it's fuel economy, did you? >:)
Nope, not for the mileage, but to be 5 mpg off of what its' supposed to get tells me something is wrong - either my speed or a problem with the car. I've been using the cruise, so I'll try altering the speed - if I can just avoid being run over by these insane Kali drivers.
 

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So, I've been noticing that I get right about 20 mpg on the highway. Mine is a 2010 R/T 6-speed, "unknown" mods (might have a tune, don't know), 3.92's, a K&N drop-in filter (had a Mopar CAI before I got it but the dealer pulled it to smog it - which is why I think it might have a tune), and currently has a Magnaflow Competition series cat-back. No other mods that would affect mileage. Traffic around here on the freeway flows at 75-80, so I'm wondering if it's just the higher speeds or maybe I need plugs/have another problem/etc. Car has 46K miles.

Any (helpful) ideas?
My 07 srt8 jeep only mods were cai and cmr dyno tune and it passed ca smog here in so ca. The 3.92 are a bear at freeway speed lol.
 

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I would look in the manual. I think 2010 5.7's have a spark plug change every 30000 miles. Any codes?
 

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Discussion Starter #8
I would look in the manual. I think 2010 5.7's have a spark plug change every 30000 miles. Any codes?
No codes. I bought it used, so I don't know the service history - or at least very little of it. I'll dig into that more. Yes, 30K is the plug interval.
 

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Nope, not for the mileage, but to be 5 mpg off of what its' supposed to get tells me something is wrong - either my speed or a problem with the car. I've been using the cruise, so I'll try altering the speed - if I can just avoid being run over by these insane Kali drivers.
I was just messing with you, so many things can effect mileage. I hope you can figure out what's going on. I know what you mean re the insane Kali drivers, I lived out there for 8yrs (84-92) and was quite happy to escape.

Paul
 

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Discussion Starter #10
I was just messing with you, so many things can effect mileage. I hope you can figure out what's going on. I know what you mean re the insane Kali drivers, I lived out there for 8yrs (84-92) and was quite happy to escape.

Paul
I knew what you meant :wink3:
 

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I know what you mean re the insane Kali drivers, I lived out there for 8yrs (84-92) and was quite happy to escape.

Paul
Oh, it's gotten much better since then :surprise:

A Guy
 

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2019 Sublime Shaker and 2010 Detonator Yellow R/T Classic
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No codes. I bought it used, so I don't know the service history - or at least very little of it. I'll dig into that more. Yes, 30K is the plug interval.
Since you bought it used and don't know it's history it might have had a tune done to it via predator or diablo, I did one on a 2010 Classic I use to own, I turned off the MDS (which consumed more fuel), changed the fuel to 91 Octane and something else I can't remember. I traded it in hat way but there was no way the dealership was gonna tell the next person what I did to it.
 

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Something definitely wrong with it. My 2010 R/T 6 speed with 3.73 gears got 28-29 mpg @ 80mph, My 2012 and 2014 R/Ts 6 speed with 3.92 gear got 27 mpg @ 80mph.
 

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Discussion Starter #14
Something definitely wrong with it. My 2010 R/T 6 speed with 3.73 gears got 28-29 mpg @ 80mph, My 2012 and 2014 R/Ts 6 speed with 3.92 gear got 27 mpg @ 80mph.
With the Flowmaster Force II kit on it I think I picked up some of it. I think I'm gonna do plugs this weekend just so I know the status of them.
 

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Discussion Starter #15
So, yesterday I drove up to Reno and came back today. I tanked up(with premium) just short of Fairfield, drove up to Reno doing 75-80, did a little city driving in Reno - maybe 25 miles or so - then made it to Auburn where I filled up. 335 miles, 15.25 gallons, 22 mpg. Not sure if it should matter but it's been 95-100+ degrees here as well. I'm starting to wonder if the cats may be plugged or something.
 
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