Diesel efficiency -- load vs. RPM

[bryson]

I drive a 2000 F250 -- 2wd, 6spd, 7.3L Powerstroke.

I've been really working on my driving style -- mostly just keeping my speed low, anticipating lights, coasting up to stop signs, etc.

Obviously the driving modifications that conserve energy (avoiding the brakes as much as possible) will make a difference regardless of engine efficiency. My main question is whether load or RPM has a greater effect.

I notice that towing my boat doesn't seem to affect the mileage nearly as much as I expected. I drive the same speed with or without my boat, and usually accelerate at about the same rate. This makes me think that load has less of an effect on a diesel than on a gasoline engine.

On the other hand, a few people have seen pretty substantial improvements by doing things to reduce aerodynamic drag -- something that contributes only to engine load.

I would love for Big Dave to chime in on this -- I would be very curious to compare the mileage difference between his truck in the following configurations:

A: With the aero bed on, but no overdrive (stock RPM, reduced drag load)
B: No aero bed, overdrive engaged (reduced RPM, stock drag load)

If Dave has any of these numbers, or if anyone has an opinion or has performed a similar test, I would love to hear from you! I'm hoping that this thread could provide me with some insight as to the nature of the diesel.

Thanks,

Bryson

[oil pan 4]

What mods have you done so far?

[bryson]

None so far -- just been trying to stay off of those brakes and keep it under 2000 rpm and 60 mph. I do end up rolling about 65 on the way to work, though -- I'll sacrifice some fuel economy to keep up with traffic.

I've been considering mostly aero modifications, and maybe some instrumentation. I don't want to do anything too bizarre looking, and I don't want to do anything that will affect practicality.

[oil pan 4]

Sounds like most of the truck users.
Then you want to get the largest air cleaner possible, feed it cold air or rammed air.
Get taller bigger tires.
Do an aero front bumper like me. Mine would already be on but I am trying to figure out how to put a big intercooler behind it.

Does that 7.3L have a turbo?
If not get one, if it has a factory turbo consider getting a larger turbine housing or bigger turbo all together.

Get a bed cover, if they are proven to help your body style and bed lenght combo.

Consider an external mirror delete and aero wheel cover if possible.
Smooth wheel covers - EcoModder
Side mirrors - EcoModder

Check out the wiki, I have added a lot of diesel ecomods.

[Duffman]

What % of that is City Bryson? I get anywhere from 16-19 MPG (US) in the city in the summer. I got a 2007 6.0 2wd 6spd.

[DevilzTower]

Originally Posted by oil pan 4

Does that 7.3L have a turbo?

Yes, it has a turbo. In addition, the Fords have nicely sized intercoolers as well.

[bryson]

DevilzTower is right -- turbocharged and intercooled.

Duffman -- it's probably 70% city driving. That's one reason I have focused more on driving style than aero mods so far. I'll probably move into aero stuff soon, but I still want to stay fairly conservative.

oil pan -- I would love to find some slightly taller tires to change the overall gearing a little, but it's tough to get taller without getting any wider. Stock tires are 235/85/16.

The truck is a regular cab long bed, so an aero cap would probably work really well for highway mileage. I'm a mechanical engineer by trade, so I've got some good software to play around with. I mostly do Finite Element Analysis, but I have done some CFD and have started up modeling a pretty rough truck with which to run some basic flow simulation. Mostly, I'm curious to see how a small "kammback" for the cab in conjunction with a partial bed cover will compare to a full aero shell.

I also would like to do some underbody work with an air dam, since I don't want to go any lower than the stock 2wd truck sits. I've also got a few ideas for the wheel wells, since I don't really want to run covers. I have tossed around the idea of doing an intake -- I don't think that it will help fuel efficiency much since the air flow rate is so low under those conditions, but I wouldn't mind hearing the turbo some more at a lower load/RPM

[oil pan 4]

Wider tires wont hurt you as much as you think they will.
If you are going to run a lower bumper or air dam it will matter even less.
Another good thing about running larger tires is they almost always have higher load capacity.

What does the stock intake look like?
Rammed air and cold air intakes are your friend.

Water injection is nice for loaded hauler diesels or diesels that see a lot of highway time.
Water injection - EcoModder

I'm going to put the front lower, may off set it with air bagged springs for when I need some more clearance, which is kind of rare.

[Duffman]

I'd stick with your existing tires, I wish I could run those on mine but the smallest rim I can run is 17". I've got a tonneau cover on mine and it definately helps, I know a aero style cap that others have done on here would help but I dont want to comprimise my visibility or ability to carry large items in the bed.

[oil pan 4]

15s and 16s are your cheapest truck tires.
15s are always cheap and 16 can be cheap depending on the tire size.
Then beyond that the bigger the rim the bigger the money.