N14 or C15 or ??? for good power and MPG?

I promise dude, it'd be happier at 16-1700. Seriously, your staying closer to peak torque right now, using more fuel and making the engine work harder.

 

You do you Amigo, but pre egr diesel's of the 80's & 90's liked to spin, especially the Series 60..

Know it seems like a far off time from today's smog'd down emissions snorting junk cruising the super slab at 1050 rpm or whatever they do, but even turning 1800 is nothing for the Detroit. My old truck had a constant duty 1800rpm 11.1L Series 60, & some days I'd be there for hours at a time. Still got decent mpg at 1800 too.. lol

I've even seen a dash plaque one time for a factory equipped Detroit tractor. It said "never pull hard under 1400". So take that for what its worth..

This the Detroit Diesel Series 60 page from an FLD operators manual. Checkout # 3..

 

My ‘89 W9 has a DDEC2, with 10 speed and 3:73 rears, on tall 22.5’s. This is it loaded. 70mph and 1800rpm.

 

We can say youre putting alot of faith in a fuse.
If the fuse blows the last time you use it, the next the jake won’t work.
It works in the trucks i currently have but some Didn’t have them.

 

I'm not trying to call your bluff, as I can clearly see her singing along @1800 & 70mph. (which imo is a ddec ii happy place) But something in the spec doesn't quite line up..



What model # transmission are you running?
I used RTX14710C for .73 final, based on being an '89 model.
14710B would be .74 final which would only change top speed ~ minus 1mph..
Or someone swapped out the rears?

 

Are 11R 22.5’s, 41” tall? To further your point, this truck has a dog gone speed limiter, at 70 mph. Would that effect it? I seriously need to rid myself and my father in law(driver) of this feature, in my truck.

 

Too my knowledge, depending on tread depth 11R22.5 will be somewhere in the vicinity of 41"- 41.3" tall..
295/75r22.5 & 275/80r22.5 are about 40"

285/75r24.5 & 275/80r24.5 are 41"-41.3" or the same height as 11R22.5's

No, the speed limiter should not affect rpm at a given road speed.
Rear ratio, transmission gear ratio, & tire height/diameter are all that come into play to determine engine rpm at a specific road speed, assuming the clutch is engaged..