Most excellent forum!

[jpgmtech]

Originally Posted by DifferentPointofView

Also remember your running a diesel Oh, and the reason I'm averaging 21 is because of a muddy fun trip I put into my fuel log I'd be averaging 22's if it weren't for it. Lately it's been 23-24.

Hey that's actually quite good considering! I just had to get that Jeep dig in there, lol!

The number I quoted was best-case on a highway trip. My mileage display was actually showing better than that, calculating verified the 9.8. Commuting with a big diesel eats major fuel. I'm still working with the De-fuel modes to try and get it better. When the weather warms up it should help a bit to. I'm going to start using the log here after my next fuel-up. But most of my winter commuting tanks (I will be riding a bicycle when the snow and ice go away around here) are around the 15 to 20 litres/100kms mark. The whole truck was totally geared for loads and towing performance, with almost no thought given to fuel economy. On the plus side, the Duramax engine is (from what I am told by engineers) the most efficient engine (per specific output) that GM has produced.

[DifferentPointofView]

Ever think about trying to make your own bio-diesel? diesel prices are off the walls right now.

[jpgmtech]

Originally Posted by DifferentPointofView

Ever think about trying to make your own bio-diesel? diesel prices are off the walls right now.

Yep. I've done considerable research on it. I don't have the time or tools at this point to get that started. But I should note here that a common-rail diesel (GM Duramax, VW TDI) is not a very good candidate for homebrews. They are very very sensitive to fuel quality! If a person was to run biodiesel in these, they need to really be careful about how they brewed the fuel.

[Achtung]

Originally Posted by jpgmtech

I live right in the smack of the hummer/diesel truck/suv land in the oilfields of alberta, so my business generally involves the worst consuming vehicles out there.

You're right about that...

Nice to see another Albertan here! I also have a truck, just a gas half ton though. Like Metro said, its good to have someone with your training. My head's already spinning a bit after reading through this thread...

Originally Posted by jpgmtech

I'll tell you about my future project (if it works out) when I have more time...

At some point I'll do a writeup on the new GM Hybrids too... I've just finished some training on them.

Looking forward to hearing about your projects and reading your writeups!

[jpgmtech]

Thanks! I'll probably be leaning toward truck stuff here for the next little while. Just bought a new bicycle for going back and forth to work with though. The D-max will burn a little less fuel sitting at home...

Just did an interesting little test today in amongst other tuning details on my truck. Found out that slower is ALWAYS better with the truck. If I can stay in top gear and go 80kms/hr, that yields the best mileage... It just drops off at any speeds higher than that. I have a spreadsheet I may post later. Aerodynamics on these things doesn't exist!

[MetroMPG]

jpgmtech: simple question for a diesel person:

Since your truck motor doesn't suffer part-throttle losses like gas engines, does that mean that, unlike gassers, the most efficient rate of acceleration is super slow granny style?

Or is it another case of, "it depends"?

I have precious little experience with diesels. Can count on one hand the number of hours I've spent driving them.

[tasdrouille]

Darin, I have had VW diesels ever since I got my license in 96, and was not able to attain higher FE by feathering the go pedal when accelerating. That's only my experience though. Whatever the engine I go with the BSFC maps when I can find them...

[MetroMPG]

Thanks, tasdrouille. I should head over to the BSFC thread and see if there are any diesel maps. I don't think I've seen one before.

[jpgmtech]

BSFC is an interesting thing with modern common-rail diesels. My theory is best FE for accelleration is right on peak torque (for any engine). That is when the fuel rate is doing it's greatest work.

If a person could have a CVT style transmission and have the diesel run at peak torque for accel, that would be optimum. Of course, on a diesel, peak torque is very low in the powerband. That would be one reason why granny acceleration wourd return better real world results.

For steady-state cruising in a diesel, the lower the fuel rate (throttle pedal in this case) the better. However that does not necessarily mean that lower engine RPM is always better, depends heavily on the gearing of the trans and final drive.