kilo6 Posted February 11, 2010 Share Posted February 11, 2010 hi guys well i made the jump and bought an 05 cxn 613 427hp 13 sp with 3.86 rears. one problem i see already is fuel mpg. running around 5.8mpg. this will be an over the road tractor so i wonder if i changed to 3.55 rears what would that do for me? great forum by the way. Quote Link to comment https://www.bigmacktrucks.com/topic/12604-fuel-milage/ Share on other sites More sharing options...
bts-4120 Posted February 11, 2010 Share Posted February 11, 2010 hi guys well i made the jump and bought an 05 cxn 613 427hp 13 sp with 3.86 rears. one problem i see already is fuel mpg. running around 5.8mpg. this will be an over the road tractor so i wonder if i changed to 3.55 rears what would that do for me? great forum by the way.5.5-6.0 is what alot of the EGR motor's are getting my pre emmision 427 is avg 7.0 3.55 rears would be alright if you was going to be running 70mph or a bit faster all the time in flat country , the taller gears will turn the truck in to a gutless wonder that may struggle to get the mpg's you have now Quote Link to comment https://www.bigmacktrucks.com/topic/12604-fuel-milage/#findComment-49411 Share on other sites More sharing options...
cgallamore Posted February 11, 2010 Share Posted February 11, 2010 i feel turning less than 1300 rpm's shortens egr cooler life and adds to coolant push problemsi just got rid of 04 had 373 gears got exellent millage over 6mpg at 60 mph, it was very sensitive to mph over 70 mph would drop it under 4mpg, mine was a 460.im glad to see you got a 427 much better motor Quote http://www.bigmacktrucks.com/uploads/1272400769/gallery_4852_794_314995.jpg Link to comment https://www.bigmacktrucks.com/topic/12604-fuel-milage/#findComment-49414 Share on other sites More sharing options...
kilo6 Posted February 11, 2010 Author Share Posted February 11, 2010 i feel turning less than 1300 rpm's shortens egr cooler life and adds to coolant push problemsi just got rid of 04 had 373 gears got exellent millage over 6mpg at 60 mph, it was very sensitive to mph over 70 mph would drop it under 4mpg, mine was a 460.im glad to see you got a 427 much better motorhi bigen i have been following your posts, hope 2010 brings less headaches. i had a 97 century 12.7 giving by the ecm 7.25 mpg great engine but the truck slowly demolished around the engine. time to upgrade. it is a pity that 8 yrs later and new egr regs that these trucks are struggling with mpg. a big step backward for sure. i love the mack look and already feel the rugged quality that these trucks are known for. i pull dry van mainly east of i-35 so i probably will not see the rockies for a while. i have a very nice lady with mack trying to find a soultion for me regards mpg and gear ratios. this should be very interesting. i will keep an eye on here for some creative solutions. Quote Link to comment https://www.bigmacktrucks.com/topic/12604-fuel-milage/#findComment-49420 Share on other sites More sharing options...
cgallamore Posted February 11, 2010 Share Posted February 11, 2010 hi bigen i have been following your posts, hope 2010 brings less headaches. i had a 97 century 12.7 giving by the ecm 7.25 mpg great engine but the truck slowly demolished around the engine. time to upgrade. it is a pity that 8 yrs later and new egr regs that these trucks are struggling with mpg. a big step backward for sure. i love the mack look and already feel the rugged quality that these trucks are known for. i pull dry van mainly east of i-35 so i probably will not see the rockies for a while. i have a very nice lady with mack trying to find a soultion for me regards mpg and gear ratios. this should be very interesting. i will keep an eye on here for some creative solutions. gerryb is at the front on keeping cxn's goingbest of luck with your new truck! Quote http://www.bigmacktrucks.com/uploads/1272400769/gallery_4852_794_314995.jpg Link to comment https://www.bigmacktrucks.com/topic/12604-fuel-milage/#findComment-49424 Share on other sites More sharing options...
cgallamore Posted February 11, 2010 Share Posted February 11, 2010 every time i tried squeezing a little extra fuel milage running 12 to 1300 rpm's is when i would have trouble, mabe the 427 will be different. Quote http://www.bigmacktrucks.com/uploads/1272400769/gallery_4852_794_314995.jpg Link to comment https://www.bigmacktrucks.com/topic/12604-fuel-milage/#findComment-49425 Share on other sites More sharing options...
cgallamore Posted February 11, 2010 Share Posted February 11, 2010 every time i tried squeezing a little extra fuel milage running 12 to 1300 rpm's is when i would have trouble, mabe the 427 will be different. whenever i would say to hell with the fuel millage and drove it like i stole it, it never gave me any trouble, but the mpg would drop to 2.9 mpg so that never lasted very long. Quote http://www.bigmacktrucks.com/uploads/1272400769/gallery_4852_794_314995.jpg Link to comment https://www.bigmacktrucks.com/topic/12604-fuel-milage/#findComment-49426 Share on other sites More sharing options...
cgallamore Posted February 11, 2010 Share Posted February 11, 2010 hi bigen i have been following your posts, hope 2010 brings less headaches. i had a 97 century 12.7 giving by the ecm 7.25 mpg great engine but the truck slowly demolished around the engine. time to upgrade. it is a pity that 8 yrs later and new egr regs that these trucks are struggling with mpg. a big step backward for sure. i love the mack look and already feel the rugged quality that these trucks are known for. i pull dry van mainly east of i-35 so i probably will not see the rockies for a while. i have a very nice lady with mack trying to find a soultion for me regards mpg and gear ratios. this should be very interesting. i will keep an eye on here for some creative solutions. i have to say the cxn is the quietest,best riding, best driving, most compfortable, best fuel milage, of any truck i ever drove. Quote http://www.bigmacktrucks.com/uploads/1272400769/gallery_4852_794_314995.jpg Link to comment https://www.bigmacktrucks.com/topic/12604-fuel-milage/#findComment-49427 Share on other sites More sharing options...
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