I run a 600 kitty that when I rebuilt it I put on a Cummins 444 turbo, one of the highest volume single turbos around (had to modify the manifold some). Had it well tuned by Cat in Orlando. Then added a variable Pittsburgh power unit, free flow mufflers and 6 inch stacks with 6 inch pipe from the manifold. According to Pittsburgh I should be putting out about 800 to 850 HP but have never had it on a dyno, know it doesn't work to hard pulling hills, empty (78500 lbs) Never worry to much about fuel miles as with what I pull I don't get any anyway.

I get 7 summer and 6 winter with my M11 Cummins. 925,000 miles. 370/410hp. Peak hp at 1800. Peak torque at 1200. I shift at 1400 with an 80,000lb gross and it recovers to 1200. I drive 60.

I guess you and I would get alot better mileage if we had 500+ huh?

Never mind the fact that the best fuel mileage truck on the minneapolis run I used to do was a cornbinder with an m11 screaming at 1700 rpms.

Truth is, you can't compare rpms of one motor vs another and say "oh, this one is running less rpms, therefore it's getting better mpg".

In fact, it is most likely the opposite. Just look at my example(and I have data to back it up) or look at cars. What gets better fuel mileage, the low revving v8's or higher revving 4 cylinders?

Interesting, Allan...

Just out of curiosity, what's your lifetime average with your D12?

Kind of flies in the face of why some companies, like mine, spec a multi-torque C15...The C13 is available with a multi-torque, 1550-1750 lb-ft, 445 HP setting...which is pretty much identical to the C15 I have now...

Other than being able to upgrade for resale value, what's the advantage of the bigger motor?

It doesn't work that hard, therefore lasts longer.
Also, tho i rarely use it, i like to know, it's here, when i need it!

I don't know if they really last longer. My dad had a detroit last 2 million miles. All engines have one crankshaft, six connecting rods, six pistons, etc...

I don't know what the lifetime average of my engine is, but last year I did 7.5 MPG on paper. Considering I average over 8 in summer, the winter really kills my fuel mileage. Canadian prairie winds suck. And the cold. And the #1 fuel.

I have a 3406 E model Cat..430 HP. 10 speed tranny and 3:55 rear ends...At 70mph I'm nearly at 1850 RPMS. I'm trying to figure out if that's too high to be running this CAT, as I usually average 72mph or more in the states I run...usually around 1900RPMS. I've been told that's too high, but if I run this truck at the " recommended" 1500 RPM for fuel efficiency, I'm doing 58mph.

Just wondering if I'm okay running the RPM'S that high....I have been for 8 months and no problems yet, but I just want to be sure....I've never had a CAT, this is my first!

Wow:bow:...never met someone who averaged that on paper...what RPMs and speed to you cruise at? Also, what HP and torque are your engine rated at?

I really cannot say what or how different trucks get different m.p.g. I have a cabover just like a brick wall going down the road. my rpms are at 1850 at full throttle. 72 mph. 1600 rpm around 64-65 mph but I have almost always got great m.p.g. it's just one of those things I dont argue about. I just do everyhting I know to get good m.p.g if I cannot then I'll look to buy aa different truck. there are way too many variables to blame or credit when calculating m.p.g.

It's not that great, trust me. If I lived down south, it would be much better.

Truck is a 1999 Volvo 770

425 Volvo engine, I think 1650 torque (425 hp at 1900 rpms)

16913 eaton tranny

3.73 gears

24.5LP tires

I cruise at 60 mph, right around 1350 rpms. It is quite gutless. I get passed all the time on the hills.