I've actually tried this little O/D on O/D off experiment in a previous vehicle of mine. I found that it was actually more fuel efficient with the O/D off, or in the case of the manual transmission I had, not shifting into overdrive.

If all we had to do to get good milage was to mainatin RPMs of less than 2000 then we'd all swap out our gears to 3.08s and get manual trannys and we'd be off. Incidentally, if that's true I could just start out in first gear and then shift up through the gears at WOT as long as I shifted before I reached 2000 RPMs I'd be getting HUGE gas milage gains.

Danco, I'm afraid you're missing the point that even though an engine is turning faster it is not necessarily burning more fuel. And since fuel economy means that you go a certain speed while burning as little fuel as possible, in some instances by downshifting and turning more RPMs you can back out of the throttle (burning less fuel) and actually gain MPGs. I understand your argument, but I'm afraid you're mistaken.--DIY

 

I remember talking to a guy many years ago that had a Chevy with a big engine in it and I asked him about gas mileage. He said it got 10 MPG if he was towing a trailer. Driving around town empty, 10 MPG, on the highyway, 10 MPG. Didn't matter what he did it always got 10 MPG.

 

Turning more RPM at the same throttle position = More fuel.

Turning more RPM at a different throttle position = Depends. If your ECU kept the A/F mixture constant over the entire throttle position/MAF voltage/RPM, then your idea may have some merit, but since it doesn't, there's too much to discuss on a forum.

There is a point of diminishing returns on decreasing RPM/increasing load. This is why other manufacturer's 5 or 6 speed transmissions still have about the same overall ratio for top gear and just decrease the spread between gears.

Gear Vendors probably won't help our trucks because the transmission will sense the increased load vs acceleration and downshift, ruining your fun.

Now, back to the topic at hand. Will using OD on the freeway increase fuel mileage? Yep.

 

Holy crap there is even video's proving my point!

I hope this is able to break through that brick wall and your over your shoulders!(Paradigm Stuckness)

http://www.care4air.org/eco_driving_...vingform.shtml

""Maintain a steady speed, using the highest gear possible to keep your engine working at its most efficient."

"Shift into a higher gear as soon as possible;between 2000rpm and 2500rpm."

here is a site with a power point on gear rpm and fuel economy!
http://www.iea.org/textbase/work/200...co-driving.pdf

 

Meh, all based on a completely different car that is an order of magnitude lighter than our F150s, which also probably doesn't have the aerodynamics of a large brick to boot.

Ever look at an ECU's fuel curves? What do you see at WOT vs 20%? You will see the target A/F go from somewhere around 14.7:1 (sometimes even leaner) with the O2 sensor having override to maintain this to a set pulsewidth that results in somewhere around a 12:1-13:1 A/F. This is a 20% increase in fuel consumption at the same flow rate point on the curve (MAF voltage).

What's my point? In a general sense, decreasing RPM can increase mileage. However, there is a point of diminishing returns on a car with EFI running on gasoline for many, many, many reasons. I would say that the best way on modern cars with O2 sensors is to keep it in closed loop as much as possible or trying to stay below 70% throttle position (or whatever the closed loop shutoff point is on these trucks).

Either way, increasing your mileage by 5-10% on a vehicle that gets 18mpg is not worth the aggravation and danger of constantly watching that tach to maintain as low an RPM as possible.

 

heres what the FORD company says;

" Driving within the "green revs
area" at approx. 2000 r.p.m.
leads to maximum fuel economy"

http://www.ford-eco-driving.de/downl...r_engl.qxd.pdf

 

yes you said somthing about trucks being larger,

"The savings to companies of adopting an eco-safe driving style are huge and the larger the vehicle, the bigger the savings."

http://www.roadsafe.com/magazine/sum.../page_100.html

 

Paradigm Shift

Think of a Paradigm Shift as a change from one way of thinking to another. It's a revolution, a transformation, a sort of metamorphosis. It just does not happen, but rather it is driven by agents of change.


http://www.taketheleap.com/define.html

 

I found it on the internet, so it must be true. :rolleyes

Notice you excluded that page's third bullet point:
That flies directly in the face of everything you've been arguing. If greater RPM means greater fuel consumption, then lower RPM must mean less fuel consumption. However, when you're engine braking, you'd still be using more gas with your foot off the pedal at 2000 rpms than you would at idle, right? So why not shift into neutral and step on the brakes if you're trying to conserve gas?

You still haven't answered the question: If it was reall as simple as running the lowest RPMs, why wouldn't ALL manufacturers simply install a 15:1 overdrive gear in the transmission for the final drive gear?? The answer is that it's *not* that simple. If Ford could get their CAFE numbers up to 60 MPG, why wouldn't they? If they refused to for some conspiracy-theorist's reason, why wouldn't the aftermarket have been making them for 25 years (since the last gas crunch)????

 

DancoDanco,

By your theory, if I'm running 2000 RPM in O/D on the highway unloaded, I'll get the same milage as running 2000 RPM in O/D pulling 6000lbs...

 

Indeed, he's focused strictly on engine RPM, not load at all. The two are not necessarily directly related. They are if you eliminate all other variables, but the only engine that runs like that is a lawnmower! Throttle position and, therefore engine load, will not be the same. Tying the two together in a modern automobile engine is a VERY hasty generalization.

 

Dancodanco just wants to argue. If that wasn't the case, he would accept that everyone has basically said that lower RPMs generally gives you better mileage. It's not always true because of all the variables, but he wants to argue that it's always true. So, let's chain his truck to a tree and see what his MPGs are when he just sits and spins at 2000 RPM.

So, once again for his benefit... yes, lower RPM GENERALLY gives you better mileage. In general, on the highway, OD will get you better mileage. But, keeping the engine at the right RPM for the load is probably the right answer...

I can find information that holds to any position on the internet. Just because it exists in cyberspace doesn't make it reality - nor does skipping the details to make your point.

Don't know about the rest of you, but if one person wants to argue and nobody responds, they are likely to stop trying to argue.

 

Yep, injector duty cycle (in other words, fuel consumption) in most cars is primarily determined by throttle position, rpm and airflow, not RPM alone. Other things like O2 sensor input, coolant temp, knock sensor activity and ambient air temp have smaller roles in injector duty cycle. Either way, simply reducing RPM won't turn your truck into a civic. When it gets down to it, it still takes about the same amount of energy to motivate your 4700lb brick.

Right.

I drive fairly normally, accelerating at a rate as fast or faster than most cars out there and I get between 17 and 20mpg (one nearly all freeway tank). Now, the worst I've done without towing was just under 16mpg driving it with the transmission shifting at 3500rpm all the time and I got 19mpg with it shifting around 1500-2000rpm driving like a grandma. Personally, I'll drive in the middle and get 17-18mpg. That extra 1-2 mpg just isn't worth it, not to mention my transmission won't appreciate me doing 30mph with the torque converter slipping the whole time too much.

Conversely, when stock, my SE-R would get about 22mpg when I drove it shifting at 4-5000rpm (about the 3500rpm equivalent of the F150) and would get 30-36mpg driving it really conservatively. In that case, the 8-14mpg was definitely worth it. Of course, it now gets about 3-4mpg on a road course on $11.30/gallon C16, but that's definitely worth it...

 

Yeah, but then what's the point of a forum?

 

You know how it is... there's arguments that are productive and then there's arguments for arguments sake. He wants to argue for arguments sake.