Reporgraming and Hacking moderm PCMs

[Ecky]

I had mine for more than a decade, and had a lifetime fuel economy somewhere around 70mpg of mixed driving. I had virtually zero maintenance from 160k to 250k miles. In the last two years I pulled the stock drivetrain out and put a hot Honda 2.4L in, giving it a 0-60 of around 4 seconds and 45mpg mixed driving, with 55-65mpg possible on the highway with a light foot. I'd get another, but they're extremely rare here.

Your observation with your Explorer is certainly puzzling. I wonder if there might be another factor at play.

I wonder if it might not have something to do with the shape? For example, ships are long enough and have enough drag that they have certain speeds where they have much lower fuel usage, and others where its much higher, due to the way fluid wavelengths interact with the hull.

[racprops]

The 03 Ford Explorer:

Curb Weight 4,381 lbs

2003 Crown Vic 3,942 lbs.

SUV is 439 pounds heavier the 03 Crown Vic

The 2003 Ford Explorer has a drag coefficient of .41 Cd.

The 2003 Ford Crown Vic has a drag coefficient of .37

The 67 Mustang had .45

VW Bug .48

[Ecky]

Originally Posted by racprops

The 03 Ford Explorer:

Curb Weight 4,381 lbs

2003 Crown Vic 3,942 lbs.

SUV is 439 pounds heavier the 03 Crown Vic

The 2003 Ford Explorer has a drag coefficient of .41 Cd.

The 2003 Ford Crown Vic has a drag coefficient of .37

The 67 Mustang had .45

VW Bug .48

How about frontal area? (I'll use metric since the math is easier)

I'm seeing the Crown Vic as: 1.44m height x 1.98m wide
Ford Explorer: 1.80m height x 1.88m wide

Crown Vic frontal area = 2.85m²
Ford Explorer frontal area = 3.68m²

Crown Vic CdA = 2.85 * 0.37 = 1.05
Ford Explorer CdA = 3.68 * 0.41 = 1.51

Going by wind drag alone, where the Crown Vic would get 30mpg, you should expect 20mpg in the Explorer, due to it having a 50% larger CdA and needing 50% more energy to push it through the air. Drag goes up exponentially with speed so you'd also expect the Explorer to drop much more steeply with speed. The fact that it doesn't, up to a certain point, is what's more puzzling.

[racprops]

Concerning wind or drag coefficient I only see that the Explorer is .41 and the Vic is .37

You say the Explorer is 50% more??

SO I divided the Vic's .37 by 2 which gives .185 which when added to .31 results are .555. That should be .50% more.

Take .37 from .41 I get a difference of ONLY .04.

So taking .04 and divide it into .41 I come up 10.25 times which I think comes out to .10% More.

That seems a LOT less that 50%.

So if my math is correct, then the Explorer has 10% higher drag, then it will only lose 10% of MPG, so taking 30MPG X .10% I get 3 MPG less or 30 - 3+ 27MPG.

Rich

[Ecky]

Not correct.

The coefficient of drag is a unitless and dimensionless number. What it describes is the shape, not the size.

For example, a battleship might have a coefficient of drag of 0.32, but you and I both know it doesn't have less drag than a Crown Vic. What it says its, if a battleship were shaped like a Crown Vic instead, it would have more drag.

A cube has a coefficient of drag of ~1.0. So, by the Explorer having a drag coefficient of 0.41, that indicates it only has~41% as much drag as if it were cube shaped.

Getting the size off Google, a Ford Explorer is 1.80 meters tall, and 1.88 meters wide. A Crown Vic is 1.44 meters tall and 1.98 meters wide.

To get the frontal area that these vehicles have to push through the wind, you multiply the width by the height. The Explorer ends up with an area of 3.68 meters squared, while the Crown Vic's area is 2.85 meters squared. 3.68 / 2.85 = 1.3, meaning the Explorer is 1.3x larger in the wind, even before you take its drag coefficient into account

The Explorer is 3.68 meters squared facing the wind, but it has the drag coefficient of 0.41. 3.68 x 0.41 = 1.51, its total drag.

The Crown Vic is 2.85 * 0.37 = 1.05, its total drag.

[racprops]

One problem is both cars are off the ground so how tall leaves out the open space under them.

Plus the avg. Explorer has much more road clearance so it is taller but not bigger.

Plus the 2000 Mercury at 1700 RPMs got 30MPG at 65MPH

The Explorer at 1500 RPMs gets 30MPG at 50MPH

I firmly believe it is engine RPMS that matter in these cases.

Rich

[Ecky]

You have a point that my math doesn't take into account ground clearance. Air passing under the car doesn't behave the same as air passing around and above, so it's not as simple as just including or not including it.

Another point is that I've simply multiplied the width by the height - the Crown Vic tapers in more aggressively than the Explorer, and is actually smaller than the numbers would suggest.

For the sake of argument, I'll subtract out the difference in area under each vehicle:

Crown Vic - 5.2 inches ground clearance (132mm), 78.2 inches width (1982mm), 225mm wide tires
Ford Explorer - 8.5 inches ground clearance (216mm), 72.1 inches width (1831mm), 235mm wide tires

The Explorer has an area open underneath it of (1831mm wide minus 2x235mm = 1361mm wide, by 216mm high = 0.294m²

The Crown Vic has an area open underneath it of (1982mm wide minus 2x225mm = 1532mm wide, by 132mm high = 0.202m²

The Explorer's corrected frontal area becomes 3.39m², and the Crown Vic's becomes 2.65m². Rather than being 30% larger in the wind (not taking into account ground clearance), the Explorer is only 28% larger. Again, not taking into account the Crown Vic's more aggressive inward taper to the roof.

Multiple in the coefficient of drag, and we get a final difference of +42% drag for the Explorer.

~

RPM is significant, as you say, and it's hard to work out through basic math just how much it impacts economy.

Some things I can say for certain:

At 65mph, aerodynamic drag is ballpark 5x larger than rolling resistance. Engine losses are highly variable.

When I put a very large and overpowered engine in my Insight, the fuel economy was around 2x higher than that of the donor car it came from (28mpg highway -> ~56mpg), and this was almost entirely due to it being more aerodynamic.

[freebeard]

When I put a very large and overpowered engine in my Insight, the fuel economy was around 2x higher than that of the donor car it came from (28mpg highway -> ~56mpg), and this was almost entirely due to it being more aerodynamic.

How did it compare with the original Insight?

[Ecky]

Originally Posted by freebeard

How did it compare with the original Insight?

Fuel economy was down by around -40% in like for like.

[cRiPpLe_rOoStEr]

Originally Posted by racprops

Looking for help reprogramming and hacking modern CPMs.

And yes I know there hundreds of tuners doing programs for PCMs.

BUT everyone I talk to will not bother or do anything to make MPG.

Most of the MPG-oriented reflashings I see ads are meant for Diesel engines, but there are some also offering their services for gassers. Mostly focused on shifting points of automatic transmissions, as it would (at least in theory) not be illegally tampering with emission devices.