Got my 78 out on the high way for the 1st time since I bought it. These things don't like over 65 do they? It handled it fine just sucks gas and winds the motor up. I got it to 85 on the gps and the motor was turning 3000. I just wanted to see what it would act like or if it would rattle and it did ok but definitely ain't like a mid 90s truck like I'm use to.

 

Yeah, since the drag force increases exponentially with velocity, these trucks suffer a lot at higher speeds. They are some of the least aerodynamic vehicles out there unfortunately.

I have a gauge called the "Scangauge II" (works on OBDII vehciles) that's in my Bronco which estimates MPG. It's always been very accurate when I compare my MPG during fill ups to my mileage traveled. When I got around 63-65 on a flat road, I get about 14-15MPG. If I try to keep a steady speed at 66 MPG, it stays at about 12-13, and at 70 it's about 10MPG.

So I pretty much am always going 64-65 because my truck doesn't like going much faster.

 

My old Bronco will run 85 all day long. Til its sucked the tank dry. In about 230 miles. Maybe.

 

I got the scan gauge 2 in my 95 f450 it's really nice and like it. On another note I'm trying to figure out what axle ratios I got. If I'm running 50ish mph with 37" tires at 2000 rpm it's got 4.10 right.

 

Gear Ratio and Tire Size Calculator - 4x4 and Jeep Ring & Pinion

 

Final Drive = (RPM * Tire Diameter) / (Speed * Transmission Gear Ratio * 336)
I'm assuming you are in a 1:1 gear.

Final Drive = (2000 * 37) / (50 * 1 * 336)
Final Drive = 4.4 (possibly 4.56 gears?)


In my '81, I'm around 2500 RPMs at 75mph, which is really nice. I get around 13 - 15mpg at those speeds too. Back when I had an overdrive transmission, 1bbl carburetor, and smaller tires, I'd get 17mpg at 75mph. They *can* do pretty well on gas mileage if they're set up right.

When all of the suspension is in good quality, they're very sturdy. Aerodynamics aren't the best, but they're as solid as a rock at highway speeds.

 

I usually try to keep mine between 60-65 because that's where it gets the best mpg's on the highway.

 

+1, 60'ish +