7 MPG Pre Egr 12.7 Detroit 60 Series 470?

You're right. If there is a MPG number on a row (mpg is in bold) that was a fill-up; otherwise it was a partial... That row's mpg figure covers all the way back to the last fillup.

I use partial fill-ups when I'm reasonably certain I will encounter lower-priced fuel elsewhere along my route. For example, 10/31 might look like a fill-up, but it was actually just enough fuel to make it to the cheaper -less ifta- fuel stop 900 miles down the road (I had estimated 6.5mpg given the 45,000lb load climbing 7000' in elevation).

As for the $50 & 13 gallons on 12/17, I had actually planned on filling at a $2.95 station a couple hundred miles ago, but I was under a hot USPS load that wound up not even having 5 minutes to spare so I had to pass by to arrive on time... That put me in a high-cost area with low tanks so I put in just enough to make it to a reasonably priced station (13 gallons buys me 100 miles).

I'm running under my own authority, but I hear mostly good things about LS...

 

I kinda thought 1250 rpm was lugging the engine but I guess not! I'm not sure I could handle driving 55mph lol. 63 so far is the slowest Ive been able to stand. I pull a 7 car trailer with mine and I've been told I should be thrilled if I get over 7mpg and so far it has. Also a lot of idle time seeing how it runs my pto

 

I get similar numbers, slightly lower, as my average gross is around 70,000 lb. Some up at the top, some less. Running around 1400 RPM in direct (16th) on an 18 speed tied to 2.64 rears. That has me right on about 61-62 mpg. My average in the last 345,000 miles has been around 7.6 for all miles, year round. I stay only in the upper tier of the U.S. Factory remanned pre-egr 12.7 Series 60 500 hp.

I took the waste gate turbo off before we dropped the engine in and replaced it with a Borg Warner 171702 non waste gate turbo. Running lower than 1300 RPM is not very productive with that turbo. I find 1400-1450 RPM is a better spot with it. I have cruised down at 1300-1325 on flat runs with lighter loads, and it does do well then. But with the frequent heavy, bulk loads I haul, it likes it better at 1400-1450 on the rolling hills.

Terry, doing car hauling really has aerodynamics working against you in spades. I would expect 7 would be very good with that.

 

1250rpm is fine up to about 150 horsepower or so, which means I have to downshift on any sort of incline. But with a car hauler's aerodynamics, you might be at 150hp just on the flat ground?

 

This makes sense seeing how we have the same turbo. You're definitely right about going under 1400 it seems to lug it unless the loads are light and the ground is flat.

So a question that I have for my situation is, with aerodynamics working against me so much, is there any point to looking into super singles? Or have I pretty much hit a brick wall on fuel mileage?

 

Low rolling resistance tires will still help, but the percentage improvement won't be the same as for a dry van. Of course the slower you go, the less aerodynamics matter...

 

Cowpie is correct that Detroit Diesel generally recommends 1400rpm for fuel economy:


(this graph is for the DDEC VI)

But that is their general recommendation based on all sorts of equipment. The power demands of a van are generally going to be lower than a flatbed which are going to be lower than a car hauler.

So here is a graph of BSFC for the 1994 12.7 Detroit Diesel Series 60 (DDEC III) from SAE (source: http://www.nap.edu/openbook.php?record_id=12258&page=36 ). It helps explain engine efficiency for various power demands at different rpm:

View attachment 76165

In case you haven't run across BSFC before, basically it is the amount of fuel consumed to make a certain amount of horsepower for 1 hour (the lower the number -- the less fuel consumed).

You can see that when power demands are below 140 horsepower, BSFC is best at lower rpms. Above 140 horsepower, things get interesting and you have a higher efficiency island between 1400 & 1700rpm -- with the island being fatter towards 1400rpm. Pretty cool to see that graph -- my own tests showed the cut-off around 150hp...

Anyway, if you are Detroit Diesel and you're giving generic advice to fleets pulling a variety of equipment with drivers who don't care about mileage -- you're going to tell the fleet to gear it for 1400rpm so their drivers can just set their cruise control and put their feet on the dash... But if you're a fuel-conscious driver pulling efficient equipment (requiring less than 130hp on flat ground) and don't have a problem slowing down & downshifting when going uphill, you will probably be better off cruising at lower rpm.

 

double yellow, how are you calculating what horsepower your engine is making in real time?

 

I'm just using the scan gauge. You can calculate it from a coast-down test if you like -- I haven't done so yet. Here is the formula:


P = m*v*[##(1+i) + g*grade + g*CR] + 0.5*ρ*CD*FA*v3


where:

P: is the power demand in watts
v: is vehicle speed (assuming no headwind) in m/s (or mps)
a: is vehicle acceleration in m/s2
i: is mass factor accounting for the rotational masses
g: is acceleration due to gravity (m/s2)
grade: is road grade
CR: is rolling resistance
ρ: is air density
CD: is aerodynamic drag coefficient
FA: is the frontal area in meters2
m: is vehicle mass in metric tonnes.