Fummins top end??

ford_cummins83

ford_cummins83

newbie
Joined
Dec 10, 2008
Messages
362
What is everybody running to get some speed out of these trucks?
I went from 4:10 to 3:73 and it didn't make much of a difference, i'm running the zf5 and around 85 it sounds like its coming apart, I know i can put the 4k's in, but thats just making it rev more and going a little faster but to get to about 120 what can i do to get there??
 
I have 3.55 with 33" tall tires. I cruise easy on the interstate, and can pull a loaded trailer at 60 in 4th gear on the 2 lane. I don't have a tach yet so I can't give you exact rpm, but by ear and feel, it is in the sweet spot.

Here is the one I use to figure my set-ups-
http://www.grimmjeeper.com/gears.html
 
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My tach dont work either but my speedo does, but it just seems like around 85 that it doesn't need to go no further.. My timing is set too high so at 80 is where i can really feel the power but i can punch it and its over again lol.
But i didn't know if its because im running the zf5 and the NV would make a difference or not.. i've heard all final drives are the same ratio and then i've heard they're not
 
If the zf is the same one in your year of truck, it should be the wide ratio tranny that has a .76 od. The NV4500 is a .75 od ratio. The close zf5 has a .77 od ratio.

You could put those in a speed calculator and see if there's a difference, but I doubt there's much. If you want to compare the 6 speeds, the zf-6 is .72 and the nv5600 is .73 of ratios.

I would say 3.55 gears would be good. Anything after 2500rpm sounds likes it's going to blow up anyway, even though its not.

Going from 4.10 to 3.73 should give you a 200rpm drop on 32" tires. 3.55 will drop that another 100rpm. A 4k gsk will do good. Youl'll be able to run up to 120mph and you won't get the defueling. Besides, how often will you be going over 85mph anyway?
 
Thats true, but i want it to be there when i try to pass someone or when were out playing at the track.. kinda sucks rapping out before you get to the end.. So switching to the nv or e4od or zf6 wont be making a difference either way?
 
The Older Dodges with the Cummins and Three Speeds used a 3.08 I think. Investigate that! With the torque of a diesel, getting off the line is not a problem. At 2500rpms you would be at 102mph on 32" tires. At 3250rpms you would be at 133mph
 
Yeah the 3:08's would be good, my 1st gear is useless anyways because its so low, but are the dodge and ford axles the same?
I already got 21* and yeah a 4k is in the plans but i dont wanna rev that thing that high just to really get some speed, think that 3:08 might be the way to go with some 4k's
 
i tried 4:10,s , switched to 3:54. i really like these gears. i run a dodge nv-4500. i ve had a couple of 3:08 geared 1st gen dodges, not a good ratio for towing. also the axles for those gears were kind of odd ball. the front was actually a dana 61. go 3:54, the 1st gen cummins ve pumped motors have a broader torque curve than later cummins so wider ratios were ok.
 
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