RPM/ MPG sweet spot for NA 7.3

[Diesel JD]

The speed limit is the same with or without a trailer in FL. I would probably voluntarily keep it at 60 just feels safer.

 

[Brianedwardss]

I have yet to get over 15 mpg on any tank since I've owned my truck. I did use a whole tank at 50 mph on the interstate once and it got me 14.9 mpg. Used gps to confirm my speedo. I keep my R's under 2400 cruising (under 60 mph)

 

[OB_WAN]

I did several tests when I was running NA. Running 55-60mph gave the best mileage @ about 17mpg. I think my RPMs were ~1500-1600. When I pushed it above 1700 RPMs my mileage dropped to ~15-16mpg.

Now running a turbo, I cruise 70mph down the freeway, am heavy as hell at times on the skinny pedal, and get 15mpg. haven't tried being easy on it yet.

In my trucks defense, it hasn't had the injectors/IP/timing refreshed in ~100k miles. Time for a tune-up

 

[Simp5782]

I am planning on taking a trip from north central Montana to Indy next month. What kind of mileage would/should i see at around 2100rpms ya think? I just swapped to 3.55's with L/S. I have the 5 speed, 38gal rear tank,19gal up front, and a 52gal aux tank in the rear that I throw in sometimes if I find a place with good diesel prices. (like in reno before u hit that 50cent higher price in cali.) i usually keep it empty tho. I am installing dual taurus fans, all aluminum radiator, new BB injectors, and maybe a retime before i go. I am also running 245/75/16 tires. Would it be better to put my 235's on? or leave as it

94 idi 4x4 turbo

 

[Diesel JD]

There's just no telling what kind of fuel economy you'll get. Some people claim regularly to see 18-20 mpg even with the 4 speed or C6 and 3.5 or 3.08s on the highway. I've never reliably seen anything over 16 mpg. I did get one tank with better than 18 mpg when I first owned my truck and was running the older #2 diesel, but that fuel had more BTU/unit than either my B100 or the current pump fuel does. I was also never convinced that the FSV wasn't letting the engine drink a little from both tanks then especially since as great as that tank was the other tank was pretty miserable. I usually find I'm either in too heavy of traffic or in too big a hurry to do what I would like and just go 55-65 on the highway and see what she's capable of. In the rare cases where I've done that I always get better than 15 if empty or light, usually closer to 16-16.5 even on B100.

 

[david85]

I was able to consistently get slightly over 24 MPG by limiting my self to 55 MPH. That included some stops and starts in traffic light areas. But thats with really tall gearing. Only Icanfixall has taller gears than me, and he gets pretty crazy mileage too - often at crazy speeds to match.

At 70 MPH I can see 20 MPG give or take.

After having my truck moosed the MPGs have been much more consistent. I had my doubts but I have to say it runs great right now (timed by ear and by feedback from MPG results). I don't know if this is true for other trucks but I was having trouble getting consistent MPG results for a while too. Some days I could set the cruise and the truck would just glide over the hills and get in the upper teens and even low 20s on RARE occasions (Non turbo, C6/3.08 back then). Other days it didn't matter how gently I drove it, the darn thing struggled to stay above 16. The other change right now is I am a religous convert to running stanadyne lubricity supplement and am trying to use it in the other diesels in the family too.

I'll never forget that first time I completed my trip and the fuel nozzle shut off at ~30 liters (usually I was celebrating to see 40). Thought it was a fluke but next week I pulled the same trip on a consecutive fillup and Bang, did it again with a calculated difference of only 0.4 MPG. Dragging the flatbed trailer at 55 in overdrive gave an equally consistent 18-19 MPG on several consecutive fillups.

If you limit yourself to no faster than 70 MPH and you can see 2100 RPM, you should be able to get the upper teens. I'll lay odds that you should get about 18.5, we'll see when you get back how close I was.

Don't think there is much difference between the 2 tire sizes there.

 

[Simp5782]

im hopin for 18-21 at 70. and 2000-2100rpms. My cruise doesnt work so it ****** me off to keep it steady. I am thinking bout that intercooler add though before i go. That would help alot. That same side cooler moves 900cfm air. Should be plenty for a factory turbo.

 

[Black dawg]

the 245s are shorter and wider.

 

[Simp5782]

Where in Montana r u blackdawg?