Engine/Transmission (1994 - 1998) fuel mpg results

[CATCRACKER]

(all unloaded)





city 14-15.



interstate doing 68mph which is 2100 rpms 15. 5-16



will going to a 255/85 tire help mpg. with the tires what will my rpms be a 70mph. i think the 255's are right at 34"s.



these trucks seems to guzzle fuel after 2000rpms.



when i went up to 2250 my mpg went down 2. 5-3mpg



what are you guys thoughts am i on target. the are calced results using the fill up method so they are close with a . 5 mpg variance



my timing is stock will it help to bump it up ?

 

[JGheen]

Just got back from my weekend trip upstate and got great fuel mileage, but have no way of finding it exactly because I never re-calibrated my odometer or speedo since I put the lift on. I couldn't tell whether I got worse fuel mileage running @ 2000-2300 rpms vs. 1700-2000 rpms. I'll ask this question, if anyone knows the answer, what is the best rpm to run at to get the best fuel mileage. I have the NV4500 transmission and in 5th gear I was running @ 1900 rpm @ about 70-75 mph. I have heard some people say that your not supposed to run in 5th gear below 2000 rpms but I since the lift and bigger tires I run at 1700-1900 rpms cruising in 5th gear and seem to get great mileage..... like 17+/- mpg.

Timing advancement will help mileage. I see you are running no fuel plate..... and you still have not bumped timing?? I would get that done SOON! All that fuel your dumping in the engine, I would definately say your mileage must be somewhat crappy with no timing advance and all that fuel. Mileage varies from truck to truck, but I saw on a website one time that regardless of the mods, a Cummins 12v or 24v should get at least 17 mpg +/- on the freeway and 13-16 in town.

 

[nfox]

CTD MPG

I pulled my 24 ft gooseneck empty 250 miles into Minnesota on saturday, and the trailer weighs 5000 pounds by itself and on the way home i had a 91 ford explorer on the trailer which roughly brought the weight up to 10,000 pounds and the wind going south on I-35 on the way home was a b**ch for the 250 miles on the way home and with my mods and 4. 10 gears i got 12 mpg, which i thought was really good. Oo.

 

[bmoeller]

Cat-



I have gotten over 16mpg in the summer running 70-75 mph. Have stock size 215 tires and 4. 10s. Cruise didn't work at the time when dad and I went out to Minden, NE. Town mileage is pretty much the same as yours. Was before the #10 also.