1991 F-250 2WD 4.9L I6 MPG estimates

[flydude1221]

Whoa 30 , with what you described for mods I think you could hit 24+ , especially if you had something below 3:1 ring and pinion, I.E. 2.73:1 (I think that is a ford gear set)


Basjoos check you PM's

[roflwaffle]

Originally Posted by Frank Lee

Like towing an 18' flatbed with up to 10,000lbs of whatever on it. Wouldn't even dream of hooking that monster on to the Ranger.

I don't think you should even think about hooking that up to a F-150. Don't get me wrong, I'm not saying that a heavy duty truck can't tow more than a light duty, but just because a truck is "full size" doesn't mean it can do a whole lot more than a smaller one.

Originally Posted by Frank Lee

And the many occasions where I had the F150 box and even the cab packed with stuff in order to make one trip or even to make multiple trips. Same job with the Ranger would have REQUIRED additional trips, using even more fuel.

If it was me, I'd slap a flat bed on the ranger so you could carry as much stuff.

[Big Dave]

I had responded assuming that Isaac wanted to do a project on this particular truck. Why not? He has little in it. At that price it is probably on a salvage title and his resale value is junk. Perfect project vehicle. Even if you foul it up, you aren’t out much.

A 300 Six in a three-quarter ton truck tells me he probably has at least 4.10:1 gears and probably 4.56:1 gears. He’s probably wound out at 60 MPH.

Both Ford 8.8 and Sterling 10.25” axles can be fitted with 3.08 or 3.31 ring and pinion sets. I use a 3.08 and find it to be quite satisfactory. Correction to earlier post: search Randy's Ring & Pinion. The Differential Experts. Auto Parts & Services. for parts.

His OEM tranny probably does not have much of an overdrive. Maybe 0.8:1 if any. The T-56 found in Mustangs has a 0.5:1 overdrive. The low gear is low enough (2.97:1) unless you are starting heavy trailers on steep hills. The torque rating for a T-56 is enough that either a 300 Six or a Cummins 4BT do not produce enough torque to exceed the transmission rating.

If doing the diesel swap is too much, maybe by cleaning up the aero and going to the numerically low gearing and a T-56 he could slow down the 300 to the point it isn’t such an egregious fuel hog. Mill the head down so his compression ratio goes up and install a more modern ignition that backs off spark advance when it hears knock. Feed the thing 91 octane gas.

Maybe Singh groove the head when milling it. These have gotten quite popular with small-block Chevy builders as the Singh groove allegedly enhances low-end torque. I think Johnny Mullet did the Singh grooves to his Metro. Maybe the Mullet-Man would care to weigh in.

Without the diesel swap, I don’t think 30 MPG is in the cards for this truck. Maybe 22-24, tops with the T-56. The 4BT3.9 is one of the more efficient engines out there and the 300 Six is a dated undersquare design with low efficiency. The diesel swap should be good for at least a 33% improvement in MPG over the 300 Six.

[roflwaffle]

$15000 for a 30mpg truck is excessive IMO when it could probably break into the mid/high twenties for ten times less. Going back to 1985, the F-150 w/ the 300 was rated at 24mpg highway and the F-250 w/ the same engine was rated at 19mpg highway. What was the difference? The transmission and overall gearing. Keep in mind, these EPA figures were adjusted versions of the original test, so at a ~50mph cruise, a 85 F-150 probably pulled closer to ~28mpg. In 91, both the F-150 and F-250 were rated for the same mileage, probably because gas was cheap and people cared more about acceleration than they cared about fuel economy. Odds are taller gearing ala the 85 F-150, and maybe aeromods if drafting showed an improvement, are the cheapest/easiest way to bump up in the mileage near the mid twenties provided the truck is in working order.

[Frank Lee]

Those fe numbers are bogus.

I've been testing the limits of pickups large and small for almost 30 years so I have some idea of what's what.

[roflwaffle]

How are they bogus? And when did you compare a 1991 F-250 M/T w/ the 300"er to the 1985 F-150 M/T w/ the same engine?

Edit- Here's the test data btw. The 5spd/I6 49-stater pulled 28mpg over thie highway cycle and 19mpg over the city cycle. The 302 V8 pulled ~19-23mpg highway depending on options (manual versus auto, FFS versus FI), and the results seem to be in line with what you get in your F250 auto (IIRC). Course 50mph average speed isn't typical of a modern highway, but that doesn't mean a 85 F150 couldn't w/ the I6 couldn't pull 28mpg@50mph or that a F250 w/ the same engine and gearing couldn't see ~25+mpg at the same speed. It also doesn't mean a modded version couldn't see the same mileage at higher speeds. In fact, if the OP can drop the same gearing in their truck, maybe fiddle w/ the fuel system too (for some reason 49-state FFS tends to get way better mileage than early FI, especially CA spec FI), they should be able to see ~25-28mpg at speeds higher than 50mph depending on how much they can drop the Cd. And they should be able to pull it off for a lot less than fifteen grand.

[Christ]

If you want to change rear gears, and you have an 8.8, get your new gearset from an Explorer. They've all got Limited Slip Diff's in them.

The 300 has enough torque to keep the truck going 60MPH with way less RPM than the OEM gears allow for. The OEM gears, I think, assume that you're not going to be doing too much driving on the highway with your new truck that was designed to WORK, not DRIVE. The F-series pickups of the days of yore were always workers.

You can swap in any 3.8 V6, 300 I6, 240 I6, 302 V8, 351 V8 transmission you find, as long as you can make the trans x-member fit between the frame rails, and you have the correct clutch disk for the trans.

One of the nice things about the 4.9 I6 is that they're all cast iron, pushrod, inline engines. They can idle really low, have torque just off idle, and if you put one of those trucks in low-lock, you can move the earth, just about. With the engine at 5500 RPM, my father can walk faster than our Ford in 1st gear LowLock. You can heat them up fairly high, and they'll take the heat like a champ, and keep on running.

It's gotten so bad in our Ford that the plastic vacuum lines on the I6 started melting and warping... and it still was running fine.

[Frank Lee]

Originally Posted by roflwaffle

How are they bogus? And when did you compare a 1991 F-250 M/T w/ the 300"er to the 1985 F-150 M/T w/ the same engine?

Edit- Here's the test data btw. The 5spd/I6 49-stater pulled 28mpg over thie highway cycle and 19mpg over the city cycle. The 302 V8 pulled ~19-23mpg highway depending on options (manual versus auto, FFS versus FI), and the results seem to be in line with what you get in your F250 auto (IIRC). Course 50mph average speed isn't typical of a modern highway, but that doesn't mean a 85 F150 couldn't w/ the I6 couldn't pull 28mpg@50mph or that a F250 w/ the same engine and gearing couldn't see ~25+mpg at the same speed. It also doesn't mean a modded version couldn't see the same mileage at higher speeds. In fact, if the OP can drop the same gearing in their truck, maybe fiddle w/ the fuel system too (for some reason 49-state FFS tends to get way better mileage than early FI, especially CA spec FI), they should be able to see ~25-28mpg at speeds higher than 50mph depending on how much they can drop the Cd. And they should be able to pull it off for a lot less than fifteen grand.

I couldn't open that link with the zip. For the '85 I6 4-sp stick I see 19 city/24 hwy. Fueleconomy.gov doesn't show a 5-speed nor any model F150 rating 28.

The old EPA numbers ('80's) were bogus, as they were something nobody but Wayne Gjerdes and Basjoos could get. I have never heard of anyone getting anywhere near that.

All the same, I don't see a gas F150 busting through 23 without, like Dave says, going to war. I don't think 50 mph cruise will do it, I don't think gears will do it. I would be delighted if someone would prove me wrong though.

P.S. I have recorded a single 22 mpg tank (recently- no cooling fan, some other tweaks) and 2 or 3 21 mpg tanks with my 302 F150 w/3.31:1 axles... over the course of 15 years with that truck. Those were the nice long 50 mph cruises with kickin' tailwinds. Since figures like that are so few and far between and the norm is 18 or less, I consider them anomalies. Fill errors or something could have contributed too.

[Christ]

Originally Posted by Frank Lee

I couldn't open that link with the zip. For the '85 I6 4-sp stick I see 19 city/24 hwy. Fueleconomy.gov doesn't show a 5-speed nor any model F150 rating 28.

The old EPA numbers ('80's) were bogus, as they were something nobody but Wayne Gjerdes and Basjoos could get. I have never heard of anyone getting anywhere near that.

All the same, I don't see a gas F150 busting through 23 without, like Dave says, going to war. I don't think 50 mph cruise will do it, I don't think gears will do it. I would be delighted if someone would prove me wrong though.

P.S. I have recorded a single 22 mpg tank (recently- no cooling fan, some other tweaks) and 2 or 3 21 mpg tanks with my 302 F150 w/3.31:1 axles... over the course of 15 years with that truck. Those were the nice long 50 mph cruises with kickin' tailwinds. Since figures like that are so few and far between and the norm is 18 or less, I consider them anomalies. Fill errors or something could have contributed too.

Won't be me trying to prove you wrong... mine's not road legal, it's just a 'Ute.

[roflwaffle]

Originally Posted by Frank Lee

I couldn't open that link with the zip. For the '85 I6 4-sp stick I see 19 city/24 hwy. Fueleconomy.gov doesn't show a 5-speed nor any model F150 rating 28.

It's actually 30mpg highway for the 4spd. You just DL the zipped file and unzip it. It pulled 21/30mpg w/ a 24mpg average, and the adjusted version for 1985 was 19/24mpg w/ a 21mpg average.

Originally Posted by EPA

F150 PICKUP 2WD 300 1M4 19 24 21 21 30 24 $ 892( 4.9L) (FFS)

Originally Posted by Frank Lee

The old EPA numbers ('80's) were bogus, as they were something nobody but Wayne Gjerdes and Basjoos could get. I have never heard of anyone getting anywhere near that.

Yeah, 50mph cruises aren't common, but they are possible. Like I said before, if the truck can get ~30mpg@50mph, then w/ aeromods it should be able to get the same mileage at higher speeds, say ~60-65mph. If you don't believe the EPA's test results that's fine, but they're still there. Which is kinda odd anyway, cuz you've posted about a diesel rabbit getting ~60mpg, even though it shouldn't because you just said it's original EPA rating of ~60mpg was bogus. That said, the EPA testing process is consistent across vehicles, even if it doesn't reflect today's driver, so assuming one vehicle can see the old EPA figures while another can't seems contradictory.

Originally Posted by Frank Lee

All the same, I don't see a gas F150 busting through 23 without, like Dave says, going to war. I don't think 50 mph cruise will do it, I don't think gears will do it. I would be delighted if someone would prove me wrong though.

The original FE testing already did. Now, that won't hold up on a typical highway commute of 70mph, but w/ aeromods it stands a good chance of holding up at ~60-65mph IMO.

Originally Posted by Frank Lee

P.S. I have recorded a single 22 mpg tank (recently- no cooling fan, some other tweaks) and 2 or 3 21 mpg tanks with my 302 F150 w/3.31:1 axles... over the course of 15 years with that truck. Those were the nice long 50 mph cruises with kickin' tailwinds. Since figures like that are so few and far between and the norm is 18 or less, I consider them anomalies. Fill errors or something could have contributed too.

I though you had a F250? And wasn't this the same truck that wouldn't take any gearing changes w/o kicking down every other second?