Better MPG's ???

[Hampton]

Hey everyone. New to the site an loving it. I have an 89 f150 2x4, 300cid, 5sp M5OD an 308 Gear. At 70 on the interstate its turning 2200 to 2300 RPM's. I was thinking about going to a larger wheel an tire combo to help get the RPM's down to around 1700 to 1800. what would be the largest size i can go to and not have any tire rub. As for the wheels i want to go with a width of 9.5'' to 10''. So how much back space can i allow. I would like to get as much tire inside the wheel well's for that sweet fat look as the end result. Thanks

[StrangeRanger]

With 3.08 gears and 29" tires, you should be turning 2075 RPM at 70 MPH in 5th. With a 2WD the best you're going to do is 32" with no modifications. If you shim the bumper, you may be able to fit a 33", not so sure about an 89. A 32" tire will reduce your highway RPM from 2075 to about 1875, but the increase in inertia and aero drag may actually reduce your fuel economy; it certainly won't help very much

[American Thunder]

I put old 16" jeep wheels and tires on my Bronco and saw a gain of about 1-2 mpg. The tires are about 31" tall, but very narrow, and run at 80 psi, so they made the ride harsher. Standard 31" truck tires will be 10.50" wide and 35 psi, which is definitely not good for extra mpg. (but they look good )
If you want fuel mileage, you need a tall, skinny tire(235/85/R16 or there abouts) with a fairly mild tread and 45 psi+ pressure rating. You can find tires like these on the 3/4 ton and 1 ton vans at junkyards, but they're all 16", so you need to find some 5-lug jeep wheels like I did or something similar that will fit on your 1/2 ton.

[Hampton]

Thanks for the info. I guess i'll seek other ways to get better MPG's. If i were to change the rear end gearing to a taller gear how tall of a gear is available? Keep in mine i drive this pickup 100 miles round trip monday thru friday to work an 90 miles of that is interstate at 80mph. Currently its getting 17mpg but i'm hooked in trying to get as much as i can.

[StrangeRanger]

There are 2.73 and 2.47 gearsets available for the 8.8" rear end. I would not recommend 2.47 gears with an overdrive transmission. They will not improve your highway mileage and will kill your mileage and performance around town.

2.73s are a different matter. They will lower your highway RPM to about 1840 @ 70 MPH which is very close to perfect if mileage is your only concern. I originally had 3.08s behind my E4OD automatic, a combination that gives very nearly the same overall top gear ratio as 2.73s behind your M5OD manual. It would deliver 19-19.5 highway with regularity. I would expect 20+ with the slightly more efficient manual, especially if you're running flatlands. 2.73 gears will significantly reduce your ability to tow or haul and may be a skosh harder on the clutch even in normal driving.

Have you considered looking at the aero drag of your truck as a way to improve mileage? Now that my truck has 3.73 gears, a tonneau cover makes a 2 highway MPG difference in my truck from 16.5 to 18.5. I consider that pretty significant. Obviously YMMV. If you have the towing-style mirrors, consider replacing them with something more aerodynamic.

[Lazy JW]

.....90 miles of that is interstate at 80mph. Currently its getting 17mpg....

Gonna be tough to improve on 17 mpg at that speed.

2.75 gears are available but it will be a dog.
Joe

[American Thunder]

The easiest way to increase your mileage would be to back out of the throttle a little to maybe 65-70 mph. The faster you try to push a brick through the air, the more the air is gonna push back.

[Harte3]

Back off to 62 mph and I guesstimate at least 1 mpg+ increase which is what I lose going 72 rather than 62.

[Hampton]

The exhaust on my pickup looks like it has 2 converters ??? and a muffler. I need to install a new exhaust system from the manifolds back. I want to keep it single and quiet. I've read here to go with a 2 1/2" exhaust. Any suggestions on what to use? And if I were to remove all the air pump an smog stuff how will this help or hurt? I'm new to this so I'm thankful for any thoughts and comments.

[StrangeRanger]

It has two cats. The first reduces NOX into N2 and O2. the second oxidizes CO into CO2. If you remove the "air pump and smog stuff" you will gain exactly zero HP and probably screw up the engine control strategy in the PCM and turn on the MIL light. You will also be in violation of Federal law and more importantly, you will be dumping crap into the air that the rest of us are breathing. If you want to replace the cats with a single 3-way high cat, you can pickup a couple of HP by doing that. If you want a quiet cat-back exhaust, the Flowmaster 70 Series should do the trick. Be sure it is the 70, the others are much louder.

[tony1963]

I'm just curious. Let's say that you improve your fuel mileage by 2 MPG. At fuel prices of $2.50/gal, going from 13 to 15 MPG, driving 12,000 miles per year, you'd save 123 gallons per year or $308.

How much will the "big tires" cost and how much will you spend trying to get there?

If you save 2 MPG at fuel prices of $2.50/gal, going from 15 to 17 MPG, driving 12,000 miles per year, you'd save 94 gallons per year or $235.

If you stopped ordering pizza one time per month at say $20 per order, you'd save $240.

There are easier ways to save a buck that call for no investment whatsoever. Also, consider driving less. Easiest way to save fuel.

[willowbilly3]

I agree with Joe, just slow down if you want better mileage. I have seen 3-4 mpg difference from 58 to 75mph on carbed stock 300s. That's worth leaving home a couple minutes earlier (or a couple hours). The wide tires kill fuel economy. I went from skinney 16s to 31x10.50s and lost about 1 1/2 mpg on my 72. Those tall gears might be ok for flatland highway cruising but I'm not a fan of them. To me 3.08 with any o/d is a pretty sluggish cog, I can't imagine driving one in the 2s.
Even if the rpm is theoretically optimum, where are the throttle plates at cruise? A vacuum gauge would tell the real story on how hard the engine is working to maintain the rpm, no matter what it might be.
I have had a couple stock carbed 300s that rocked on 20-21 mpg (at 55-60 mph) with no overdrive and 3.50 gears. One was an econoline with an C6 and it would do 19 all day long cruising 65 with 2 Harleys in the back...until I decided to rip all the emissions stuff off to find that elusive horsepower and mileage it supposedly cloaked. Then it never got ove 17.5 ever again.lol I was young, much younger then.

[StrangeRanger]

Even if the rpm is theoretically optimum, where are the throttle plates at cruise?

That wasn't theoretical, it was empirical (i.e. observed) data over several thousands of miles with the 3.08 gears in my F150. Because of the difference in OD ratios, 3.08 gears with an E4OD gives the same overall top gear ratio as 2.73s with an M5OD. The 3.08/E4OD combo was good for 19+ highway, including a Knoxville-Akron run over the WV turnpike and many north to south runs through OH. It pulled hills well and hardly ever dropped out of OD. It was a stone around town, but his question was highway mileage. The 2.73/M5OD should at least the equal the mileage I experienced.

As to the gear ratio, If you compare the overall reduction of a T-18 starting in 2nd gear with a 3.55 final drive (which is 3.09 x 3.55 = 10.96) to an M5OD starting in 1st with a 2.73 (3.90 x 2.73 = 10.65) you'd see there's not much difference. You lose the creeper gear for getting a trailer moving, but again that was not his question.

Personally, I'd leave the 3.08s in it and concentrate on cleaning up the aero. There's probably more MPG there than in the gear swap.

[Lazy JW]

.....

Personally, I'd leave the 3.08s in it and concentrate on cleaning up the aero. There's probably more MPG there than in the gear swap.

Yup. Particularly if one insists upon driving 80 mph. Aero drag increases with the SQUARE of velocity; double the speed and the drag QUADRUPLES.
Joe

[80broncoman]

Dropping the speed is by far the best way. unless you want to GREATLY improve the aero by putting the 300 in a 87-88 Thunderbird. (Yes I know that is an EXTREME example)

Look at how I learned how much speed matters on mpg:
99 Wrangler 4.0L on a vacation trip in Sept 08.
MPG @ MPH
14.5 @ 75
16.5 @ 65
17.5 @ 60
If you graph this out it is NOT a straight line I ended up setting the cruise @ 63 MPH on this trip.
19.5 @ 50 when I drive it to work. (19 mile drive though the rural contry side All 2 lane roads)

[mutt]

5 MPG drop fora 25mph increase in speed. so a 30% increase in speed results in.......a 25% increase in fuel consumption . And I think youll find consumption steady up to 50 mph. I think. And as you say: its not a straight line.
Ill be headin out D Day, 1340 miles, and doing some speed/mpg comparisons. Damned hard stickin to 50, tho. 60-65 is easier, but already up on the curve.......
"When you ride above 55, you ride with the ibn Saud family"?

[tony1963]

A wise old gentleman once told me that 95% of a vehicles mileage (MPG) is based solely upon the vehicle that you choose. In other words, you can only gain about 5%, regardless of what you do, short of installing another engine, etc.

My suggestion would be to simply drive less or drive slower.

I wouldn't be spending $800 just to save $250.

[THE FRENCHTOWN FLYER]

Hey, all you guys who recommend driving slower are pretty darned smart. Works for me.

[American Thunder]

I'm getting the highest mpg cruising around 40-50 mph in 5th gear. At 40-42 mph, the truck hits a sweet spot, where everything just feels and sounds smooth and perfect. I take mostly back roads on my commute to work and back, because I love cruising at that speed, for that reason. Well, and for the 22 mpg.

[willowbilly3]

Even if the rpm is theoretically optimum, where are the throttle plates at cruise?

That wasn't theoretical, it was empirical (i.e. observed) data over several thousands of miles with the 3.08 gears in my F150. Because of the difference in OD ratios, 3.08 gears with an E4OD gives the same overall top gear ratio as 2.73s with an M5OD. The 3.08/E4OD combo was good for 19+ highway, including a Knoxville-Akron run over the WV turnpike and many north to south runs through OH. It pulled hills well and hardly ever dropped out of OD. It was a stone around town, but his question was highway mileage. The 2.73/M5OD should at least the equal the mileage I experienced.

As to the gear ratio, If you compare the overall reduction of a T-18 starting in 2nd gear with a 3.55 final drive (which is 3.09 x 3.55 = 10.96) to an M5OD starting in 1st with a 2.73 (3.90 x 2.73 = 10.65) you'd see there's not much difference. You lose the creeper gear for getting a trailer moving, but again that was not his question.

Personally, I'd leave the 3.08s in it and concentrate on cleaning up the aero. There's probably more MPG there than in the gear swap.

Sorry, I never heard of the term empirical before. Is observed the same as recorded? I admit I don't know much about stuff like brake specific f c or the aero/drag calculations. Mostly just seat of the pants performance and recorded mileage. for me, I liked the 3.55 final gear and the pulling power it had. Getting 19-20 with sensable driving made it seem like a nice combo. I only drove one F150 with AOD and 3.08s and it could smell a hill for about a mile before you got to it. O/D was for flat ground only and no head wind. It never made 19.

[Harte3]

Emperical evidence can be observed, depending on the expertise and honesty of the observer, but is best recorded as opposed to the "wow" seat-of-the-pants" anecdotal testimony which is deceptive at best. Marketing types are big on pushing a very loose "theory of gains" with no empirical evidence, observed or recorded, to substantiate the gains.

[Harte3]

An example of observed empirical results would be the significant difference in power when running winter blend diesel or straight #2 diesel pulling heavy loads in a big truck. On the blended fuel, I would have to drop one gear on most grades that I would pull in the next higher gear on #2 fuel. That was 101,000# GVW loads in the Pacific Northwest...hated using that blended fuel.

[Hampton]

Well i slowed down to 65 and have gained around 1 plus MPG. Going to try 70 and see what i get. That 3-way cat, Who's it sold by? Can i just go to any muffler shop purchase it with the 70 flow master and get it installed or will i have to get it from a speed shop and take it with me when i get my exhaust redone? And is there any one cat best to use or are they all the same. And from what i have read 2 1/2" is the size exhaust i need to go with for best results?

[willowbilly3]

An example of observed empirical results would be the significant difference in power when running winter blend diesel or straight #2 diesel pulling heavy loads in a big truck. On the blended fuel, I would have to drop one gear on most grades that I would pull in the next higher gear on #2 fuel. That was 101,000# GVW loads in the Pacific Northwest...hated using that blended fuel.

Yeah, I guess that's the same thing I call seat of the pants, when you know how one vehicle goes over a given hill with a similar load. I pull trailers with my pickups quite a bit and compare how well they do it with other vehicles. I don't use a truck just to haul me around much anymore. I have found that my Subaru 4x4 wagon does 95% of what I used to use a pickup for.

[StrangeRanger]

Empirical does not mean seat of pants, it means observed experimental data as in: fill the tank just before getting on the highway, drive 5-600 miles, fill the tank when you get off the highway, calculate the mileage, repeat.

Summit sells Catco converters. Whether your muffler shop does or not is a question you'll need to ask them. Whether they'll even install a system you bring in is also a question you'll need to ask them. most shops like to make money off the parts they install as well as off the installation.

In order for them to legally replace a converter, it must be either clogged or damaged. I assume you know how to use a hammer and chisel?

[Asa]

In order for them to legally replace a converter, it must be either clogged or damaged.

really?
that's weird, i wonder why

[StrangeRanger]

Part of their control-freak need to prevent "tampering"?
The bureaucratic assumption is that the OEM converter is somehow better and therefore cannot be replaced without necessity.

[Asa]

hrmm
i wonder what happens if you add a cat system to a vehicle that didn't have one, then later decide you don't want it (i've been thinking that one day i'll add cats and possibly an AIR system into Susie, inject the air into the cats, not the exhaust ports)

hey SR, not to derail or anything, but while i'm thinking about it, your sway bar look like this?

[American Thunder]

An example of observed empirical results would be the significant difference in power when running winter blend diesel or straight #2 diesel pulling heavy loads in a big truck. On the blended fuel, I would have to drop one gear on most grades that I would pull in the next higher gear on #2 fuel. That was 101,000# GVW loads in the Pacific Northwest...hated using that blended fuel.

The 20% kerosene of the winter blend does drop power, because kero has less energy in it than #2 oil, but it sure is nice to have when the cold weather hits. My boss has forgotten to order the kero mix before in our outside tank, and my wrecker gelled up and stalled in the sub zero weather. Fun stuff.

[Hampton]

What other things should i do to get the most MPG? This pickup has been a great daily driver from day one and is completely stock. And with 317000 miles it doesnt burn a drop of oil. Also whats so important about having brass terminals in the distributor cap? I looked at mine and they aren't.