Whats MPG is everyone getting in there bull nose 6.9s? Im getting 14 wondering if i can get better. I mostly drive at 55 but i do play around on the roads occasionally, stomping on the accelerator when i pull out of the drive.

 

You don't say if yours is a 4X4 or not, but looking at your avatar it looks like it so I'd say you are doing okay @ 14. Neither of the transmissions available then, the C6 and the T19 had overdrive so you're dealing with a 1 to 1 final ratio. Then add the dead weight of the 4 wheel drive equipment you're fighting physics to get the mileage you have.

My '85 F250 4X4 SC when stock with the 6.9 and T19 and 3:55 axles got me 12mpg at best. Now that I have the new drive-train with the ZF I'm getting better, but don't have enough miles on it yet to get an average.

My '84 F250 2X4 SC 6.9 C6 got me a faithful 15mpg.

Those wide, aggressive tires don't help you with mileage, you want to run tall skinny tires for less road restriction and lower RPMs.

But no matter what, you're getting almost twice the mileage of a 460 powered truck so you're still money ahead.

 

id like to get my hands on a zf tranny so thath the engine aint running at higher rpms i can hear that motor when im going down the road id say its at round 2000-2500 but not for sure dont have a tach. I recently got my truck straight piped so im sure thats helping the mpgs, it better cause its WAY to loud for what i like.

 

My truck: 1986 F350 6.9L NA Crew Cab Long Bed 4x4, 4.10's stock tires and Gear Vendor .78 overdrive...

17 mpg with gear vendor ON
15 mpg with gear vendor OFF

Does not seem to matter very much what speed I drive, the mpg is very consistent unless heavily loaded it drops to ~12-ish. The above numbers are highway mileage.

Edit: even in overdrive it revs too much, so it is getting a ZF in addition to the GVOD. That and some other mods will hopefully push me towards 20 mpg, but with the quality of diesel fuel declining it may be a mirage that I never reach...

 

85 6.9 4x4 c6 35" tires 3.55 gears banks non gated turbo, pump turned up 3 flats... 55-63mph I get about 10-12mpg, a/c on or off doesn't matter.. Cruise control is the same milage. I pull a 7k trailer and get 10mpg, I have a new pump with injectors..

 

My 460 truck with 3.55:1 and ZF5 on 35" tires gets 12.5 MPG at 70 MPH unloaded and 10 MPG towing about 5500 lbs at same speed.

My 6.9 turbo with 3.55:1 and C6 stockheight and tires gets about 12.5 MPG at 70 MPH. Towing same 5500 lbs it gets 11 MPG but that's losing speed up every hill and dropping to as slow as 35 up longer steeper hills where on the same route the 460 will hold 70 MPH. The 6.9 would benefit from a ZF5 unloaded as best MPG of 14.5 was averaging 40-55 MPH. 5th would be useless towing as it has trouble pulling any incline at 2600 RPM so no way it'll hold speed at 2000 RPM like the 460 does up most modest hills.

Cost per mile is about the same average $.31/mi in past year with the 6.9. That is 8.25/12.08/14.46 as worst/avg/best MPG. It gets the edge as diesel is about the same price as 93 octane but I dump my filtered WMO in the tank so it gets a few gallons on free fuel now and again to bring the average down. Just my experience with MPG on both a 460 and 6.9, hopefully informative.

 

Ah, yes, the 460 phenomena, once Al Gore invented the internet the 460 found a place it could get double digit fuel economy.