I just got done driving 315 miles (after accounting for gears) on 20 Gals. This is with 38" tires and 4.88 gears. The best I have ever got is 14.2 MPG. I only have three explainations: 1. I bypassed the smog pump. 2. I was driving 63 MPH. (I usally drive 75) 3. I put a shift kit in.
I cant see how a shift kit could help millage. So it must be one of the others. I will check again soon at 75 when I get new rubber. (My tires are out of ballance and vibrate bad at speed.

 

The wind drag is about 40% less at 63 mph.

 

Another vote for wind drag, the bypassed smog pump adds pretty much nothing unless it was seized.

 

that is amazing millage on a 351 if you ask me pushing 38" tires

 

Hey any thing over 12mpg with a 5.8 is good.

I would just be happy while it lasts and give your Bronco a wash. She deserves it for mileage like that.

 

I am kinda afraid to post this ! My 93 5.8 has gotten 17 at 70 w/air and some mixed roads. I check my odometers on at least a 10 mile run on the interstate and check several tanks-----all using my good eye! Dont throw anything big enough to really hurt-----Merry Christmas

 

Fuel milage at speed is all about aerodynamics. These trucks don't have any to begin with, and a truck jacked up with the drivetrain hanging out and big tires makes for a lot of extra wind drag. The gearing is what is helping your milage at lower speeds right now, but I bet you'll be lucky to see double digit numbers at 75mph where aerodynamics plays the biggest role.

 

For every 10mph over 65, your effective aerodynamic drag DOUBLES. Good figure though for the setup

 

Oh, and when I had my 96 5.8, I was averaging 17 (full Bassani exhaust and 31" tires)

 

You mileage is also affected by elevation. The best I get is 12.6 with my 5.8 at 4330 feet / 1320 meters above sea level.

 

My trip was efectivly at sea leval. (maybe 100 ft) I got the new tires on and will be making the return trip on the 27TH at 75 MPH. I let you know.

 

I can get 15 if I keep it at 65 with my stock 3.55 gears and 31 x 10.50 tires.
At least it doesn't do any worse than 12, even when towing my boat and going 70-75.

 

...I got less than 10, but that's with a 351 and a C6. I think it did better around town than it did on the highway, but I don't think it was really that much difference. At 63MPH I was rolling at 3K RPM's, that doesn't help much either.

 

I have been doing a lot of local driving lately (since I retired ) My TC is a replacement for the OEM and has more stall than I like. With the E4OD and the lower, low gear in it, it dosnt need a lot of stall when not towing. My TC locks at ~45 mph, that seems to be the strategy.

I am going to figure a was to bypass with a switch on the dash, a toggle for the signal to the LU solenoid in the tranny that I can fully control. I pretty well have the wrg figured out, but may need some external switch (such as the MSD rpm controlled sw), to insure that it unlocks when attempting to stop (lights, signs etc.). With the present stall, no doubt local driving mileage could be increased by locking up the converter just off-idle.

The 351 has plenty of torque for normal driving. Also, with a heavy load the lockup could be delayed until much higher speed, such as reaching cruising speed in 3rd or possibly even OD. You would probably need a heavy duty external cooler for the tranny when not locked up. A dummy load will have to be supplied back to the PCM to keep from kicking a "soft" code. Even then, a soft code will not trigger limp home mode----I dont think

I dont do any heavy off-road stuff, so my case is slightly different than some. Off-road to me is driving across a gravel parking lot to get to the boat ramp! FIRST THING NEXT MONDAY-(yeah right)

 

i am sporting a big 11.2 mpg.. I wish I was getting 17's.. I would be happy with 15's lol... and mine is a stock 91 EB addition.. sigh