Yep, its a healthy E4OD (If there is such a thing) on the 460. And, your probably right the c6 will cost some in fuel. I still think some of these rotten mpg readings might be from odometer error.

 

That could be very true about why they show lower MPG. I don't remember what size the factory tires are on my truck, but it has 31x10.50's now, and I have a GPS unit (Garmin Novi 260) and my truck is EXACTLY right on the mph according to the GPS. 40mph exactly on my speedo = 40mph exactly on the GPS. Same with 25mph and 60 mph (the ones I tested at).

With that in mind, my taller tires put my speedo right where it should be. It should show a slower mph, but now it's correct. With that in mind, it seems that the factory size tires on trucks would 'show' a worse mpg, higher speed, and wrong mileage.

What do you all think about that?

 

Try this,ont worry about the mph yet, just track the miles driven on GPS against your odometer miles driven. I switched out speedo heads on my old ranger and found a 9mph difference on just that. I just dont trust 25yr old speedos any more! On that same old ranger, I found that my odometer was 14% low against actual miles driven because of the 31x10.50s and speed was almost 10mph faster than indicated on the speedo. It was 186mi on odometer vs. 200 actual miles driven, that can screw up your mpg reading in a HURRY. I found the proper speedometer gear for the tire size and now the speedo/odometer are accurate. Sometimes old worn out speedo/odometers just arent accurate for reason of just being old!..In your case, maybe the previous owner had the same size tires on it at one time and took them off before selling and had "accurized" his speedometer/odometer like I did.

BTW, On that old V6 4x4 Ranger the difference in mpg readings after doing the math went from mid teens mpg to low 20smpg

 

That's interesting. I'll give that a shot next time and let ya know my findings.

 

I will have to try out that GPS idea and see if my odometer is off. thanks everyone for the advice.

 

You dont even need GPS, just time it through the speedometer check section on the freeway ( set the cruise on 60mph, if accurate should be 60 sec. flat) Any more or less will tell you about your odometer/ speedometer........I bet if you travel the 1 mile section at indicated 60mph, your odometer only shows 7 to 8/10ths of a mile traveled.

 

cable speedo's use magnets to drive the needles, odometer is geared. mph could be off and odometer on...

my 88 has no problem getting over 15 with normal driving, all the smog stuff on it. i have a post about it in the mpg/alternative fuels forum.

my 84 capri got 21 running 90 mph. but it had 2.73 gears and an aod and tall enough tires it wasn't even turning 2k rpm. and it had a 2bbl holley (and ~2psi fuel pressure- wonder it even ran) and cast iron manifolds. I put an edelbrock, headers, and 3.73's in it, but can't check it again untill i replace the tranny it burned up afterwards...

 

Yeah, Odometers are gear driven and should not fail, but for whatever reasons they do. Had one in a GM product, the little plastic gears that drive the number display deteriorated and only made intermitant contact. Odometer was WAY off!

 

My 85 Bronco (5.0L AOD, stock gears, stock tires, CA emissions) has never gotten better than 12MPG. I assumed this was normal, until a friend told me he got 18MPG in his 89...and he had a 5.8L. So after asking everyone I meet with a Bronco what they get (usually around 15MPG), my pet theory is that the 5.0 has to work just a little too hard at moving all that weight.

Of course, my theory is contradicted by the online claims of those few with the Inline 6 engine that they're getting gas milage in the low 20's...so I'm not entirely sold on my theory. But I would be interested in hearing from anyone who started out with a 302 and then swapped engines.

Could it be possible that bigger might actually be better?

 

I would disregard those few claims myself, and go with the average, and your real world experience. There are many cars with small v8's that would be hard pressed to get 20mpg, much less a heavy boxy truck. They must have been running downhill the whole way, and not going over 45mph.

Being easy on it, 15mpg seems the average. You are just a little below average with 12mpg, so you might want to do a tune-up and replace the oxygen sensor. I assume it's fuel injected? Possibly you might have an optional higher rearend gear too? And also, make sure the tires are pumped up, I usually run them at the max sidewall psi number. Also make sure your e-brake cables are not rusted and sticking, causing the brake to drag.

 

1991 f 150 2wd long box 5.0 efi aod with 88,000 gets 16 to 17 hiway.

 

How the hell did you get 24. The best I have ever gotten was 18. I usually get 16.

 

LOL! All i did was take it REAL easy when taking off, and just stayed in OD at 55.

 

entirely possible. my dad has an 82 f250 that he pulled the 400 and dropped in a 302 for gas mileage, and lost 1 or 2 on average. both sucked more fuel than his 76 250 that was setup the same with the exception of the year and having a dove 460.

im working on stting up a fuelie 6 in my 84 bronco, but need to rebuild the financial a bit before i can continue. i will let the board know though.

BTW. the last two days driving 80 miles to work, mostly mid sized hills, accelerate going down and letting off going up, my 88 turned 16.7 mpg- i had to check my math twice!

 

im not sure whay you guys are getting such bad fuel milage ive got a 81 f150 with a 460 fueled by a 4 barrel holly carb and i still average 8-9 miles to the gallon on the highway