Over 65mph
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Posting Guru
Joined: Aug 2007
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From: Cato Arkansas
Over 65mph
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.
Fleet Mechanic
Joined: Dec 2006
Posts: 1,925
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From: Phoenix, AZ
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.
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.
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Posting Guru
Joined: Aug 2007
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From: Cato Arkansas
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.
Postmaster
Joined: Jan 2013
Posts: 3,512
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From: Panama City
Moderator
Joined: Dec 2007
Posts: 7,986
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From: Boise, Idaho
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.
Postmaster
Joined: Apr 2008
Posts: 4,724
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From: Rogersville, TN
I usually try to keep mine between 60-65 because that's where it gets the best mpg's on the highway.
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