What RPM are the most efficient for DD 14.0 L open for 490 h

You are getting terrible mileage huh??? LOL Those rears are what is killing your mileage. Your slowest ratio that I would recomend will be 3.70. If your running only up to 80,000# a 3.58 rears will allow you 65 mph @1500 and about 6.5 mpg (loaded) to 7.5 empty

1650 is a bit on the high side. 1500 is the correct speed for best mpg on most vehicles (even personal vehicles). your bandwidth for shifting should be 1300 on low end and 1700 on high end. Lower and your hurting your engine, higher and your tearing the engine apart.

 

if you can keep it at 1450 more for you.

 

4.63 gears are pulling gears.

Out here on B doubles or road trains, those are the sort of gears we run with 22.5s'.

 

I hate to be a nitpicker but many of you drivers around here have an idea in your head of what "lower" and "higher" gears are that is bassackwards and need a short lesson here...

A 4:63 ratio is an extremely LOW ratio.. not "high"... 4:10's, 3:73's, 3:70's these are all LOW gears.

Most people used to run "the best of both worlds" with 3:58's or 3:55's back in the pre-DPF era.

3:42's, 3:36's, 2:93's these are very HIGH gear ratios - the long legged ratios that let you stretch the truck out to 100mph at 1400 rpms (or thereabouts) - and these seem to be the most common ratios these days with the EGR/DPF P.O.S engines now a days...

I don't know about Detroits but Cat Accerts after 2004 hardly anyone specs
lower than 3:36 the lowest I would try with one would be 3:42's. I don't mean to come across as a ######## with this post but 4:63 sounds ridiculously low for most of your normal highway applications in North America... I don't know what terrain you run in is like (flat? hilly? big mountains?) and I dont have a clue what the sweet spot on a 14L Detroit is but a buddy of mine has one with 3:58's and he likes the setup for what it's worth...

 

Thanks Rollin Coal, get so tired of people saying that. Low number, high gear. High number, low gear. Get it right people!