Here is the link to the DIY web page for that particular episode, if you are interested. They are definitely claiming an increase of about 10 mpg.

http://www.diynetwork.com/diy/shows_..._45859,00.html

 

I put Tru duals on my 2000 4.6L drove it to school (290 miles) got about 1.5 improvement. i was happy with it. sounds good goin down the highway too.

 

Why? Back pressure?
Thanks.

 

loss of tq-actually 2.5 wiil move the tq higher up in the power band vs 2.25-hence the reason i used it-phil

 

I see.
Thanks again.

 

Most of the hero's on these shows add up the supposed gains of all the mods and that's where they get the 10 MPG's. It doesn't really work that way. Some may add, some may be advertised to add. To them, they are all good and worth your money. Especially when the parts manufacturers are probably paying for the good words. You're better off reading about people that actually tested these things to see if they do as claimed. NCSU was right, if they really made that big of a difference, Ford would have figured it out a long time ago.

 

Dozer has the right idea.

The bottom line is this... don't do these mods strictly to improve gas mileage. Unless you drive tons of miles, you'll probably never see the full payback based only on gas savings. The main reason to do these changes is better performance and better sound.

But, that said, a slight increase in gas mileage is an added benefit. It just won't pay for the mods.

 

Alright, so my previous comment got me thinking. So I calculated theoretical payback on a mod. Lets say you spend $1000 to add new headers and exhaust (this is a low estimate I think?) and get a 1 MPG increase in average fuel economy. With an average cost of gas being $3.50 (hopefully this is not a low estimate) you would have to drive 60,000 miles to break even.

So depending on what kind of mod you make, you might see payback in a couple years... or less depending on your driving.

(1)Mod Cost $1,000
(2)Average MPG before Mod 14 MPG
(3)Average MPG after Mod 15 MPG
(4)MPG Increase 1 =B3 - B2
(5)Average cost of gas $3.50

(7)Savings per mile $0.0167 =B5/B2 - B5/B3

(9)Miles for Payback 60,000 =B1/B7

NOTE: I did this in Excel. All the numbers are in column B and the row numbers are in (). The equations I used are in italics if you want to make the calculations for your truck and mods, or check my math.

 

It's all about fluid dynamics. A bed cover offers more surface area for "down-force" requiring the truck to work harder to move against the wind. Without one the wind "swirls" and moves in different ways, that I can't even begin to understand at this point in my career/schooling, that greatly reduces the amount of downward force from wind.

The only advantage I can see from a bed cover over an open bed is the fact that it's more wind "resistant" due to the painted surface and smooth edges.

Make sense?

That's why leaving your tailgate down does NOT improve gas mileage. It simply puts more downward force on the bed. Sort of like a plane's wing. The longer area receives more force.

 

Yep... down force is a bit of the factor, but turbulent flow is the more important part I think...

Turbulent flow reduces surface drag. So not having a bed cover and leaving the tailgate up creates a more turbulent flow over the back half of the truck and reduces the drag. The same idea applies to golf *****... adding all the dimples creates a turbulent flow around the ball and makes it fly further.

 

Well I'm pretty sure it was the Mythbuster's episode that I saw too. They did a test with a soft Tonneau cover, hard tonneau cover, a bed topper, and an open bed with both the tailgate up and tailgate down. I don't remember the whole conclusion, but they did find that the soft tonneau cover had a slight advantage over no cover with regards to aerodynamics and improved fuel economy. The hard tonneau cover provided the same resistance as the soft, but with added weight. They concluded that with the hard cover you actually hurt fuel economy due to the added weight, so if fuel economy is of concern you'd be better off without a cover. They also concluded that having the tailgate down was worse for fuel economy than having the tailgate up. This may have not been Mythbusters but another magazine's test. I read alot of stuff so I get the sources mixed alot of times

 

I have seen the episode where they took two f150 crewcabs and took them down the interstate with one tailgate up and one down. The problem with this is that it was not in a controlled eniroment. Their different driving styles and the other people on the road played a factor and the one with the tailgate up got better mileage. They did a test with a exact scale model and water with a dye in it to simulate a wind tunnel. The thing to me that this showed is that with a 5.5 foot bed the air almost will make past the tail gate before it can apply any force down on the truck. Now if you have an 8.25 foot bed the air should take a nose dive at about 6 feet just like the 5.5 foot bed. So it is applying down force and getting hung up in the tail gate causing drag. Basiclly, the longer the bed the more beneficial it is to leave it down.

Now, I have run this test on my truck. Everyday my commute is 72 mile round trip with 90% highway and fill up every week and don't drive except to work. Did 4 weeks with it up and 4 weeks with it down using the same gas station. I got an average of 0.7 mpg better with it down. So run your own test, that is the only way you will ever know.

 

Yeah for all I know they could have been testing an 8' bed. This is going off of fuzzy memory In the end the full topper had the greatest benefit, but the weight of it made it useless in terms of fuel savings.

 

actually you miss understood that episode they said with the tail gate down does not improve your millage makes it worst because with the tail gate up causes a huricane affect that keeps the wind going over the tail gate and doesnt press you back down, which by then lifts the front = less airo dynamitic. With the cover it takes away the huricane affect and leaves the wind just going over the tail gate. though i tell you guys

 

I can vouch for the bed cover I built mine out of 3/4' treated plywood and Rhino coating I got 2-3 mpg improvment @75-80 mph everyday all day on the highway I can afford to run my Mickey atz's again