Ok, I know there an extreme amount of variables that can come into play gear ratios, tire sizes, load and rpm, as well as other factors. My question isn't regarding how many miles per gallon you are getting, but if ther are some charts that show gallons per hour used at specific RPM's. I have a boat in which if I pay attention to the speed too much, the RPM's increase, and simultaneously fuel consumption increases exponentially.

For me, in the marine diesels, there are fuel consumption charts based upon the engine RPM's. I would love to see the same info for our new 6.7 engines.

Thanks for any and all help.

 

Interesting. I like the idea. Hope somebody out there is an engineer.

I also think it would be nice to know the maximum efficiency with max torque and horsepower. For example, I run at 72MPH a lot, which is about 1700 rpm. I would like to know if I am getting the most energy out of the fuel I can at this RPM. I suppose it's the same question but backwards to the way you present it?

 

That is because your marine diesel is connected to a propeller which follows basic pump laws where power is a function of speed cubed. So that means when you want to double propeller rpm the power input from the engine has to increase by a factor of 8.

Wind resistance has a similar effect on fuel consumption. I was bored one day and figured out that at 65 mph my 6.0L had to produce roughly 50 hp on a level road, to raise speed just 15 mph to 80 mph engine output had to nearly double. I now own a 6.7L and the "sweet spot" seems to be between 65 and 70 mph

 

I travel frequently between Chicago and Bloomington Illinois. Putting cruise control on 65 MPH I get between 19 and 21 MPG depending on the weather. At 75 MPH I lose about 2 MPG. With winter fuel I lose between 1 and 2 MPG, depending on what part of the state I fill up in.

 

My initial question might not have been clear enough, sorry if that is the case, I am looking for engine RPM fuel consumption charts or tables. I.e. at 1600 RPM the engine under load will burn xxx gallons per hour, at 1700 RPM it burns xxy gallons per hour.

This information for me it would be another indicator for my target driving speed with the rpm's in mind.

 

You will not get any charts. as what load do you want? if there driving charts the load is forever changing. The only way you could get what i think your trying to get would be on a dyno. with that said i think your outta luck.. Your target driving speed and load will never come close to dyno results, Maybe a dealer would let you drive a used one for a while. Good luck in your quest

 

What you are asking for is easy to do for a boat since the load never changes on the hull provided similar sea state when comparing, there are no hills to deal with and when the boat is on plane the weight carried does not drastically affect fuel consumption. Different calculation completely for a vehicle where simply driving up a hill will change fuel consumption drastically, as I stated before above probably 50 to 60 mph the largest load is drag assuming the road is flat. under those conditions at 65 mph I get roughly 21 mpg. Doing the math that means I burn 3.09 gal/hr. A 2% grade will change that to 4 gal/hr. I get on average about 9 to 10 hrs of operation per tank. I recently took a trip to Florida from Upstate NY and over the 1256 mile trip my average was 2.96 gallons per hr. I used my odometer, trip hour meter, and gallons pumped from my fuel receipts. This includes mostly highway but some city driving. What you want could only be generated on a test track to develop curves. and would only be useful under those exact conditions and probably lower than the 2.96 gal/hr that i got on my 1200 mile trip.

My boat on the other hand is good for about 7 gallons per hr at 3000 RPM. I got that data from boattest.com and validated it with some testing on my own.(I was able to find a similar hull/exact engine setup.)

 

The gph is calculated with a given engine against the prop curve. Prop load vs rpm shouldn't change as much with external variables as aero on a truck load does.

You could do a plot for fuel consumption vs rpm but you would have to do it for 6th gear locked, 6th gear converter, 5th gear locked, etc. This would also vary with ambient temp, wind, humidity, etc.

The vehicle OEM's usually have figured the best combination of rpm and gear ratio for max economy. For older than 2007 vehicles this was at 55 mph (where the EPA rating is). 65 for newer vehicles (that have an EPA mpg rating). As such, sometimes you lose efficiency either side of the EPA speed.

Case-in-point: I drove a 08 K1500 a few years ago. It has 5.3L with cylinder deactivation. Per the dash display 63 mph was 17mpg on 8 cylinders. 67 mph was 17 mpg on 8 cylinders. 65 mph was 20 mpg on 4 cylinders.l The cyl deactivation complicates it a little but the point is that the powertrain control was optimized at 65 mph.

 

Thank you everyone for comments. It appears that the fuel consumption per hour versus engine RPM's is not available. Thanks for all the commentary regarding miles per gallon. I realize there are variables including loads, external factors such as wind resistance, but it was my thoughts right or wrong if I am running at 1700 rpm's in 5 th gear or 6th gear, the fuel consumption per HOUR would be the same, the variable would show up in the miles traveled. Just as in the marine industry, my sail boat burns X fuel per hour at a specific RPM. The variable shows up in distance travelled. I.e.the current if it is helping you or hurting you, just like the wind either helps you in our trucks or hurts you. My particular boat is a sail boat, and the wind usually helps, but the constant is the consumption per hour. The turbo boost in the marine engine is boosting as I go up swells, and goes away as I desend swells. Usually it is more predictable than the roads in the pacific northwest, but if you are traveling round trip on highways,the climbs and descents balance out.

My goal with the questions was to try to find for myself a target RPM range to travel in. Usually I travel within a few miles of e posted speed limits, but I have been known to push that driving north to south through the middle of Nevada.

Again, thank everyone for your help.

 

Marine Diesel fuel burn (GPH's) are more easily calculated due to constant loading @ specific RPM (given a fixed pitch prop, clean hull, mean tides and currents, wind etc) On-highway engine operating conditions vary greatly depending upon operation, weather, roads etc. Easy rule of thumb is, the less engine rev's per mile the better fuel efficiency. So keep your RPM's as low as possible at all times. Of course this operation requires monitoring things like EGT's etc. This is the reason why I am so dead against automatic trans, you simply are never in the right rpm range no matter how good their programming is.