3/4-ton Diesel
 

Hi folks, I just wanted to introduce myself.

First off, the vehicle I drive is quite a bit different than most of the vehicles that I've seen on this site--my 2007 Dodge Ram 2500 weighs in at around 3 and a half tons and has an engine displacement of over 400 cubic inches (6.7-liter). That being said, I think my turbocharged Cummins and I are doing pretty respectable--3 tank average of 25.3 mpg. This is compared to the stock mileage of around 14.5 mpg (Note: the EPA doesn't publish official numbers for trucks this size).

Most all my gains so far have come from powertrain modifactions & driving style (gotta love that manual 6-speed tranny). I'm now also usually running without windshield wipers. What's nice is I have the style that pop on or off is about 5 seconds. If it looks like rain I usually just put the driver's wiper on.
I'm looking at getting into the aero-modding area. I'm designing an aero-cap and looking at some other things as well.

Anyways, I'll throw this question out there:

"What are the biggest things that change when you're dealing with a big turbodiesel pickup as opposed to a small gasoline compact car?"

-Dave

Welcome to EM! You posed a, er, um "odd" question. But I'll play.

Your ability to wear a cowboy hat while driving.

Being now able put stacks on the vehicle and it doesn't necessarily look wrong.

Becoming the "go to" person when it comes time to move house.

You can laugh in the face of physics and thermodynamics, ie, "hey, my Cummins can put out 600hp and 25 mpg @ 7000#s!"

A suspension lift won't look silly and out of place.

When barrelling down the road at a high rate of speed, folks will get out of your way, immediately.

Choices for parking spaces diminish.

Ok, well let me give you some examples of how things change.

1) My pickup has much, much more mass, therefore much more momentum, therefore I can coast a considerably longer distance.

2) I can't do engine-off-coasting because there's no way to steer that thing without power steering. That being said, idling is comparatively more efficient with a diesel (no throttling).

3) While a grill block-off would help aero and help the engine warm up faster (decreasing heat losses), BUT it would also have the effect of decreasing the effectiveness of the intercooler, therefore, intake temps come up, decreasing engine efficiency.

4) Insulating the exhaust manifold helps a turbo diesel by sending more energy for the turbo--it wouldn't have much effect on a naturally aspirated engine (other than reducing under-hood temps.

5) I played around some with pulse-and-glide without noticing any benefit. Maybe I'm not doing it right, but 2 things that are different from a gas compact car are A) The larger, more massive engine takes more energy to re-accelerate, and B) There is tubo lag, so the engine may be much less efficient in a "pulse" than it would be staying steady.

Right now, I think the aero-cap is going to be the biggest improvement I can make. Anyways, just some of my ideas about things that are different. I'm interested to hear others' opinions & ideas.

Thanks, cleanspeed, I appriciate the humor!

I do think that people are much less likely to be upset with you for going slow in front of them---Don't mess with the guy in the BIG truck!

Pulse and glide is mainly of use with gasoline engines whose throttles have pumping losses that the pulse reduces.

There's a couple of guys here running Ford F-350's, one of whom (Big Dave) is getting around 28mpg with the benefit of some aero mods.

I am more of an engine and driveline guy, and I like the Cummins. The unfortunate thing is that Dodge and the other OEMs put final drive gears in the axles that are too numerically high for high mpg. Big Dave has a Powerstroke with 3.08s and a Gear Vendors OD along with mods that are in line with what you want to do. Do a search on this site and see what he did.

Bolt ons? A Smarty Programmer with a custom economy tune and a finding a way to get your cruise rpm down to 1400-1600 rpms.

Dave, would you mind sharing what powertrain modifications you have done?

Thx, Ed

Right now my cruise rpm is about 1800 rpm most of the time (when I'm on the highway). This works out to be 60 mph. Idealy I'd like to slow down a little bit more but here in Indiana the interstate speed limit is 70 mph, which means most people are going around 75 mph (65mph for semi trucks). I feel like going anything less than 60 mph almost becomes a hazard.

As far as the powertrain modifications go, I'm not sure how you all roll on this site. I'm all for sharing tips, but you see, some of the modifications I have made may or may not be considered legal by the EPA ;).

I've seen some of what Big Dave has done and am very interested. I plan on making some of the same mods. Interestingly enough, he's a Hoosier too.

What, you did a DPF delete? With the 6.7, they do have legal mods so that you can retain your emissions equipment and not lose power. You just have to get the programming right.

Dave, I didn't mean to put you in a difficult situation by asking that question. I have an '04 305/555 Quad-cab, SB, 4x4 and I'm just looking for all ideas to make this truck get better mpg. So far, the electronics that I've researched will give lots of TQ and HP, but not fuel mileage increases. As for aerodynamics...there's a few suggestions out there but aero-body kits don't appear to be in big demand by RAM owners. I watch Cumminsforums, and others. While there are some wild claims there's no solid, independent, testing behind the claims. Thanks for responding though. -Ed

cleenspeed, technically any modification (including re-programming) that would result in increased emissions is considered illegal by the EPA. That being said, I have never heard of any individual being prosecuted for modifying their own vehicle.

Most people don't realize this, but for a modern diesel engine the EPA regs (for nitrogen oxides and particulate matter) are THE single biggest thing that hurts fuel economy. I work in diesel R&D, so I could go on and on about this. For a truck like mine there are 2 big things: the EGR system and the DPF. The DPF is the bigger of ther two. You lose mpg's because of the huge exhaust restriction (several times what it would be otherwise), because of the fuel used to regenerate the filter, and because it prohibits good driving styles (you have to be in lower gears in order to keep your rpm's up, and you can't idle much because the DPF gets cold and will plug up).

Ed, you have a 2004 so you have EGR but no DPF. You'll see quite a bit of mpg improvement, but not as much as post-2007 folks.

You're right that most of the programmers and other mods are advertised as producing higher TQ & HP, but, in most cases there's significant mpg improvement as well. They're not advertised that way for two reasons: 1) technically, they're not street legal so the companies advertise them "for off-road use only" 2) many guys do use them to increase TQ & HP. Some of that increase comes from burning more fuel, but a lot of it comes from increased efficiency.

It's complicated, but in simple terms high in-cylinder temps boost thermodynamic efficiency, however, they also lead to more nitrogen oxide (NOx) emissions. The programmers make changes to things like injection timing which results in higher efficiency but also higher NOx levels than what the EPA allows.

For post-2007 trucks getting rid of the DPF & EGR and reprogramming can result in over 30% mpg improvement. And I'm not just throwing those numbers around--that's from data I've collected myself.

Yeah, I never liked the way most OEMs are doing this, even though it looks like all are using other strategies.

Trust me, the OEM's don't like it either but they don't have a choice. If you can't meet the EPA regs, you can't sell them--no matter how efficient they are!

Those are some nice mileage figures Dave. My 96 auto has never seen 20 since I purchased it a year ago. In retrospect I should have been shopping for a manual, but I wanted it to be easier for my wife to drive while towing. She drives a clutch OK but it is a different world when you miss a shift at 17,000 pounds on a hill getting started out.

EDIT: I got 21 on my last tank! I guess I got the teenager back into the box.