Why am i not getting good MPG?
 

Hey everyone, i posted this over at f150online a couple days too but thought i would post here also

Well i just got home from a 300 mile trip.

anyway about 175 miles of the trip was flat and i had it at cruise control on 65

the other 175 were kinda hilly and going over one mountain pass and had it at cruise on about 75

by the time i pulled into my driveway, my truck computer said 15.2 mpg and my gryphon said 15.1


what im confused about is people like FishChris (on f150online) who said towing his boat he gets 16 mpg.

heres the modifications i have done to it

2008 Ford F-150 Lariat Supercrew 4x4
True Dual magnaflow exhaust with an X pipe
Gryphon programmer with custom tunes
33' BFG A/T's 18" XD monsters
K&N CAI
3.73 gears

City driving which is 95% of the time i only average about 12-12.5 mpg and never really get above that

i drive pretty conservatively too, no rabbit starts. I also do live in Seattle which has alot of hills but i would think i could get better than 12.5

now i didnt buy my truck to get good gas mileage but i just wish i could get some better mpg than i am getting

somebody said with my exhaust i probably lost some low end compression, this would hurt me going up the hills, is that true?

do you think i should try my custom towing tune? any other comments?

I am sure Jack and others will jump in here too, but MPG reports are like fishing stories!!! (especially when the user's name is FishChris):smiley_roll1: So take it with a grain of salt. Tire rolling resistance will make a big difference. a highway tread Low rolling resistance tire could easily net +1 or more MPG's. Wind resistance is a big factor too. I'll see if I can find a graph to illustrate that and post it. Asphalt vs concrete highways will affect MPG too.

well i did just change my tire size to 2541mm which it should be with 285/65/18 tires.

the programmer said it was at like 2742 or something

hmm i didnt know asphalt and concrete made a difference!

Here is an in-depth article on MPG and tires. there are a couple of interesting diagrams on page 40 that show where energy losses occur in automobiles.. There is also reference to road surface effects on MPG
Tires and MPG

Try using your custom tow tune.

But like Southpaw addresses there is a lot of different factors out there and they all add up for you or against you.

Take for instance:
Tire type.
Tire wieght.
Wheel weight.
Gearing.
Cai.
Exhaust.
Cats.
4x4.
Headers.
Trailing weight.
The list goes on.......

Lars

Fuelly F150 MPG's

Is a good link to get more realistic MPG's

Well just to put my 2 cents in here... The 33'" tires aren't helping the mpg (heavier tire and more rolling resistance) My first thought was you might haven't correct your speedo with the turner...but I see that you did. Wind also plays a factor. But two of the biggest things is 5600 lb truck vs hills equal bad gas mileage, and anytime you get over about 65 in these trucks throw the gas mileage out the window.

Here is a little data I gather about my truck on a 280 mile round trip. Most of this is interstate. I found that if I put cruise on 67 mph (65 according to the gps) I can get around 18.9 Droping down a little more will get me 19,4+
I also found if I put the cruise on at 77(gps=75 actual speed) I drop down to around 15.5-15.9 Sometimes a little lower but thats about the average. Now before I get slammed for anything I said the conditions was pretty much the same on winter blend fuel running canned level 2 3.73 rear end. Also mpg was being calculated by miles driven divided by gallon's of gas, not programmer.

But just to throw this out there if I run around 55 pulling the ole bass boat I can get around 17.5 then the mileage drops after that. But with the tire upgrade coming those figures will be off now :doh::woot:

Southpaw and Lars pretty much covered it. I know Fishchris' truck, because he did a TON of postings in the "Appearance Products" forum in f150Online when he was getting his truck.

The boat he pulls is very lightweight, something less than 1000# with the trailer. His truck is an SCab, not an SCrew, so it's somewhat lighter than ours. It's 2WD, not 4WD like ours. It has 17" wheels. I don't know what his gearing is, but I suspect it's lower than 3.73.

So, everything I know about his truck tells me he SHOULD be getting better gas mileage than we do.

I averaged about 15.5 mpg in just under 1400 miles on our last trip at 70-75 mph (hand calculated at each fillup). I get around 12.5-12.7 when we pull our 3600# trailer. My tires are 275/65-18 Goodyear Wrangler Silent Armors and they have a fairly conservative tread - I'm sure mine have less rolling resistance than yours.

Both you and I have more bells and whistles in our trucks than Fish has. For instance, we have climate control, and it's ALWAYS on in my truck. That consumes energy.

I don't trust either the Gryphon's or the truck's MPG displays. The truck's is always lower than the Gryphon's average numbers and my "hand calculated" results fall between the two.

One point - unless your loaded tire circumference is correct, your speed and odometer values will both be wrong. For my tires, I've subtracted 3% from the unloaded tire circumference. Using Bill's calculator, that corresponds to a 7% rubber squish (since the wheel doesn't squish). I don't know what your unloaded circumference is, but you might try entering a value that is 3% lower for the tire size. (A larger number shows up as higher speed and more distance driven per tire revolution - and, when the Gryphon's speed readout is correct, the dashboard speed will be 2 mph faster, but the odometer will be accurate).

Finally, each truck is an "individual". Some will simply perform better than others and there's not a whole lot we can do about it.

Two more posts appeared as I was writing this "book". :) The "fuelly", site was quite interesting, Southpaw. Looks like the trucks getting about 15 mpg are in the majority. And JWBFX4's remark on the tires is dead on!

- Jack

ill trade ya fuel economy cory!

Its me again. I searched for miles per gallon and find this thread. I just had a few question about my gas mileage. Before I start, let me say that I know that my 35" Nitto Trail Grapplers that weigh like 80lbs. a piece are a BIG factor in my mpg loss. Here are the facts..which within lies my question. With my mods (K&N FIPK and Flowmaster 50 series) and my 35" tires, but before I ever got the Gryphon...my MPG would vary between 12-14. Now when I got the Gryphon but only had canned tunes...I ran the canned 87 Tow tune. Mileage around town was about the same, maybe a little better. On the interstate however (going like 75) I was getting around 15. This made me happy. Now maybe I was thinking wrong, please tell me if I was, but I assumed when I got my custom tunes and ran the custom 87perf. that I would get better MPGs. Well going around 50, I can get like 16-17, going on the interstate (70-75) I am getting right at 11. Whoa now. What happened? Is the custom perf. supposed to give the best gas mileage? Let me also throw in that I am NOT out to get 17-18,hell even 16 Mpg, and I know I have a big 4x4 truck not a car. And I also know it is pretty much give and take with power and MPG. I just need to know if this is normal. Thanks yall...Travis

Oh yea...before Gryphon...MPG probably not accurate seeing as how my odometer was thrown off by the tires. But with the Gryphone running canned tow and custom perf. I adjusted the tire size to correct everything. Just thought I would add that in there.

F150 Man 4Eva, what I think is happening to you on the highway is that the air resistance might be getting you. I'm going to use the metric tire sizes (235/70-17) as an example because the first number is the width between the sidewalls, I'll also use the sidewall ratio of 70 to find height. A 30 inch tire is usually around 235 mm wide but a 35 inch tire is about 345. Since the width has to increase with height then by going up 5 inches on total diameter then you add 11 cm or close to 4.5 inches in width. If you hold your hand out of the window going 70 you'll see how much wind resistance just a small area must overcome.

I'm also not a firm believer anymore that adding small amounts of height (like a 2.5 inch leveling kit) causes as much drag as I hear on other forums. I think the mpg drain comes from the bigger tires that come with the lift for most people. I added a leveling kit but my tires still had a few miles left so I didn't upgrade them. I still get about 17-18 mpg going 85 down the highway(average from gryphon before and after the lift)...and my truck isn't exactly what people call aerodynamic. Just the CB antenna alone causes enough drag to notice in a heavy head/crosswind.

The tow tune is designed to improve performance under heavy load. From the engine's point of view load is anything that keeps the truck slower than what the driver wants it to be. Watch the load next time your using cruise control on the road. When you go down a hill you'll see the load go down, when you go back up the hill the load will go up. Adding drag is the same thing as adding weight from the engine's point of view, it still has to work harder for the same results. When the engine works harder it uses more fuel. I'm not sure why the canned tow would do better than the custom performance though. Does the custom get better mileage in the city though?

Hey I appreciate your help and explaination. My main question was about the MPG differences between canned tow and custom 87 perf. City driving seems to be about the same. All is good on the custom 87 perf. until I get about 60 or above then it really drops. This is watching Instant Economy. I noticed two big changes from the tow tune to the perf. My K&N is so much quieter. That drone is all but gone. The other thing is the TC locking up. Before when I would hit about 45mph in 4th, the TC would lock. Now I can get up to 60 and it won't lock. I pretty much have to let off of the gas for a second, let it lock, and then resume speed. I don't want to come across like I am complaining, because I am not. I love the way my truck and tranny are performing. Its just that when I was getting 15 MPG highway, I was excited. I wasnt getting that before the Gryphon. But now with the custom perf..I am way below that. So I don't know what to think

Well dont really consider the instant economy readings. The average economy is a rough estimate at best. Next time you get on the road switch the instant econ to average and see how those numbers look. And if you want to make the torque converter lock sooner you can go into the custom options menu and lower it 10 mph at the most.

4Eva, wind drag is really a very serious hit on your fuel economy. The difference in drag force (which is a constant load the engine must overcome just to maintain speed on level ground increases according the the "square" of the speed. So, a 17% increase in speed, which is what you see changing from 60 to 70 mph, works out to be a 36% increase in load on the engine.

Let's assume the drag force on the truck at 60 mph is 1000#. The engine has to generate enough power to overcome that 1000# just to keep you at speed. If you increase your speed to 70, the engine has to generate power to overcome 1360# (That's 1/3 more power needed - which equates to a significant increase in fuel consumption.)

And, if you increase your speed to 80 mph, the force you have to overcome increases by 78%! (More than 3/4 more power needed!)

Now, I'm NOT saying your mpg figures are reasonable. I'm just saying all this to "quantify" the effect of speed. I USED to get about 15.5 mpg if I cruised in the 60mph range, using the "canned" level 2 tune. Now, using my custom 87 economy tune AND with my DIY "Gotts" style intake, I've discovered I can get about the same economy in the 70 mph range. So, tunes and mods CAN help.

But - a headwind will absolutely KILL my gas mileage!

- Jack

Good figures. I knew the resistance was exponetial but I couldn't remember well enough to be sure. That 4x4 package must be really heavy for you to get those numbers because your truck is naked compared to mine. :hehe: I've got the grill guard and CB that have plenty of wind resistance and I get 16-18 (by hand calculation) as long as I dont have to stop at traffic and lights.
But I also have custom tunes and the gotts mod. I'm thinking about making a ram air intake but with the 4.6L setup it is really difficult getting stuff to fit right. I wonder how that would affect my mileage if I ever could.:hmmm: I'll try it whenever I get a good design worked out.

One other thing to pay close attention to is the timing. At lower RPMs with even a modest load, timing can drop to almost zero which can seriously affect fuel economy. This is done in order to help prevent detonation under those types of load conditions. Larger tires compound the problem by dropping the RPM at certain speeds.

For example, my Expy with 3.31 gears gets better fuel economy at 80 than it does at 75 because of the load and RPM range. Oddly enough though, it also gets good economy at 65 which, despite the lower RPM and load range, I assume is due to the lower wind resistance at that speed.

One other thing to remember is that in order to help reduce droning from the CAI kits, we remove the modified Cam Timing curves and revert back to the stock ones. This has a slight economy hit as well.

Take care.

Yipes! This also means my interpretation of the effect of combining a custom tune with a commercial CAI is somewhat wrong! The custom tune actually DOES reduce the effectiveness of the CAI a bit due to the reduced timing. (I guess we could call it an unfortunate interaction). Reduced timing means reduced power, and, a corresponding reduction in fuel economy.

I'm sure glad I'm using my homemade CAI!

And, larger tires will mean lower rpms at any cruise speed, so, the reduction in timing can be an additional hit on top of the increased moment of inertia of the larger rotating mass as well as larger frontal drag due to more surface area and the increased rolling resistance of the bigger tires.

- Jack

Jack,

Keep in mind that I am referring to camshaft timing, not spark timing. The spark curves don't change when running a CAI.

Wow, this is getting pretty technical. Is there any definitive answer to the question, is my K&N setup helping or hurting me? And after all of this, I am assuming that getting lower MPGs on my custom perf. based against the canned tow tune isnt alarming.?.? Thanks again

The K&N setup isn't exactly hurting you but to eliminate the CAI drone Bill has to go to a stock cam advance curve which isn't as good for performance. I would expect that the tow program would have modified cam curves for more performance while also having a richer fuel map to help on towing. With a CAI you usually have to use the richer tow program to keep from running a lean engine. The stock cam settings may be what are lowering mpg.

I also remember that you are running big tires. They are effecting the spark timing by effecting the RPMs.
As Bill said earlier when the RPM is low the engine load goes up resulting in the spark timing getting dropped to lower the chance of detonation. By lowering the timing you also lower both performance and efficiency. If the truck isn't regeared then your timing is getting thrown off because the RPM's aren't high enough. Also since you are slinging around more rubber the load goes even higher, dropping the spark timing even more.

Well said Colby.. so to put it very basic, you want the drone of the CAI gone so Bill pulls it down to stock cam settings, thus lowering power and MPG. the timing drops at lower RPMs in order to prevent detonation during certain loads. now you have larger tires thus compounding the effect of those loads and helping to create your worse MPG.

Try playing around with different RPM levels and calculate your MPG on paper, not computer.

And colby, you don't have jack that is messing with your aerodynamics. your bumper might weight 100lbs and your antenna ain't jack. heck my antennas that i used were much more than yours is, yet no difference in any mileage or anything and my truck already has the aerodynamics of a brick... haha. then again, it is a diesel, not a 4.6. LoL

OK, so we're talking valve opening and closing times. Thanks for clarifying that, Bill. Forget EVERYTHING I posted in my last post, since I was thinking spark timing. I'm sure the valve timing has a somewhat similar effect, but nothing like what I was thinking.

- Jack

F150 Man 4Eva, if you want to try what tatsch said you can go in and adjust your 4th gear shift and lock points. Raising them will usually hurt your mileage and lowering them will do the same on performance until you get the RPMs back up, but every truck is different.

Naa, I don't really want to go in and fool with anything right now. It isn't like it's a problem..just something to get used to I guess. My AVG on Gryphon says 13.6 right now and trucks comp. says 12.6. I am gonna give it some more time and see what happens. But I do tend to keep my eye on that INST ECON. and it isn't pretty. Oh well I guess. Let me ask this though. Does the drone sound indicate running lean or can they exist seperatly? I definitely want my truck running like it should, but at the same time...if taking away the loud sound is hurting my MPG...I would say bring the drone back. It never really bothered me anyway..I kindof like hearing the power when I hit the gas. But is that drone only there because the truck is running lean and/or not as it should?

The drone is only a harmonic vibration, like blowing across the top of a bottle. The big thing on the side of the stock intake is a resonator that takes that sound out for that particular setup. The reason Bill tunes out the drone is because after a while people get tired of it and then ask him to take it out.

On the stock intake those chambers are called hem-holz silencers.
For give me if I spelled the name wrong but I'm close. :)

I was going to say the name too but I couldn't remember how to spell it either. :hehe:

Helmholtz! Sheesh! :disbelief:

Here's a Wikipedia article on it: Helmholtz resonance - Wikipedia, the free encyclopedia

Note near the bottom it talks about reducing drag on aircraft bu 40% using acoustic liners based on the Helmholtz principle. This effect was something I was a bit concerned about when people talked about removing the resonators from intakes. I thought it might induce standing waves in the intake that would hurt its efficiency. I think that is why "drone" is probably NOT a good thing too.

- Jack

Thanks Jack!
:2thumbs:
I was close but no cigar!!!!!!

Ah, you guys opened yourself up for that! I just couldn't resist! (At least no one called those things "mufflers")!

- Jack

Same here, its just not easy to prove when people think that cutting it off will make the intake more streamline like the aftermarket CAIs. :hmmm: