Anyone have any luck with bigger tires, shallower gears (3.55, 3.27), or manual hubs? while 65mph might be the speed limit on I-15 in salt lake, it's a good way to get involved in an accident.

Sounds like my biggest problem is rpms, i'm pushing 2200@75, 2300@80
to bring my rpms down to 1822@75, i'd need to run 3.27 gears and 33" tires.

 

a exhaust and intake will not help. did not help me. not one bit. i installed the intake at my buds house and drove home with it. just under 4 hr trip at 65 mph the whole way with cruise. did not change. the millage did not change when i went back this time with the 5" exhaust. do the mods but do not expect the mpg increase. if it is over 10 psi or 2k rpm's say goodbuy to the mpg's. plain and simple.

 

Ain't that the truth!!!! On my old commute from Sanpete to SLC I was averaging 17mpg with my 07 5.9 6speed 4X4 with 4:10's driving the "average speed" for the roads which you well know is 75+ I run 285's also. I tried doing 65 the whole way a few times and saw 19mpg. Only mod at the time was the kitty was gone.

 

Yes, if you can drop your RPMs down from 2000 to about 1700 or 1800 you'll probably see 2mpg better. Technically, your truck should be able to pull empty or lightly loaded at 1500rpm. If you do run larger tires, go taller, but not wider. If you keep 245 highway tires on instead of 33"x11s or 12s, you'll improve a lot.

Like someone said, intake and exhaust don't really help. If they did, every truck would come with more free flowing intake and exhaust systems. As I said before, another good thing to try is a 205 degree thermostat. If you keep the engine running hotter, your efficiency will increase. Basically, it comes down to a) aerodynamics b)rpms c) engine operating temperature d) load and e) tire size. Of course, speed is in there too, but as you said, you can only go what traffic dictates to be safe.

 

exhuast and intake helped me you must drive a ford

 

I would get an intake and just do a muffler delete. Shift at 2k or below and keep your rpm's below 2k when driving on the highway. I also would get a Quad max mileage or even their XZT which is a 65 hp tune I have seen mileage gains of about 1 to 4 MPG's better when doing this exact thing. Main thing is don't get in a hurry to get up to speed.

 

yea that last part the cumminsrig put in i think is very important, i use to try to get to speed as quick as i could, and run the gears as fast as i could.......now after driving all day i got kinda "lazy" and started to take my time between gears, and red light, and i actually noticed a pretty good difference in mpgs. maybe a couple of miles, but then i usually lose that by hot roding someplace along the way.

 

I've learned that anytime you go over 1800 RPM your mpg starts to go down and anything over 2000 RPM it drops fast. Now if you want the best mpg you would need to drive at no more then 1600 RPM's.

Also I see so many think you drive an inline diesel engine just like you would a gas or diesel V style engine but you don't. Take the time and notice that a semi driver with a Cummins engine takes his time going through the gears and not in running up the RPM's real fast, thus they use the TQ of the engine and not the HP to get it moving. The same should be done with our engines as they are made to put out power at lower RPM's then a V style engine and thus give better fuel mileage between 1550-1900 RPM's and why it drops off after 2,000 RPM's. Yes our engines can run all day at up to 2900 RPM's but they do not get good fuel mileage at high engine speeds.

 

Slow down!

 

I've always heard keep it below 2,000 RPM so I always have. BUT this past week I put some highway miles on and ran 80-85 with a 3.50 gear automatic & get the same mileage. I average 18.7 by hand calculation. Best I ever saw was on a road trip (700 miles); kept it at 70 below 2 grand and got 22 MPG. (No load figures)
I've also heard that running power service silver fuel treatment increases mileage but haven't seen that either. I mix 8 ounces of Marvel Mystery with 16 ounces of PS & run 10-12 ounces per tank.