a couple of posters on here are Cummins repower suppliers/dealers
Cummins 4BT & Diesel Conversions Forums
Registry Diesel Transplanted 80 series Registry (7 Viewers)
- Thread starter Stone
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a couple of posters on here are Cummins repower suppliers/dealers
Cummins 4BT & Diesel Conversions Forums
need a little help
hey guys i've ran into a little issue with my 91 fj... i swapped in 12 valve cummins with a nv4500 behind it, behind that is a 19 spline split case.my problem is gear ratio... in 5th gear i'm running 2200rpm to do a little over 70mph. i cant find anyone that sells a higher gear set for my stock 91 fj80 axles. im thinking a about a 3.73 would be perfect. or i'm open to the idea of a divorced od but i'm having a difficult time figuring out which one would work the best.[/ATTACH][/ATTACH]
hey guys i've ran into a little issue with my 91 fj... i swapped in 12 valve cummins with a nv4500 behind it, behind that is a 19 spline split case.my problem is gear ratio... in 5th gear i'm running 2200rpm to do a little over 70mph. i cant find anyone that sells a higher gear set for my stock 91 fj80 axles. im thinking a about a 3.73 would be perfect. or i'm open to the idea of a divorced od but i'm having a difficult time figuring out which one would work the best.[/ATTACH][/ATTACH]
in Europe, the factory turbo diesel 80 came with 3.73. I've been looking for a set for some time, still haven't found one.
what size tires are you running?
what size tires are you running?
37 12.5 bfg allterrain
thats interesting.. didnt know that.. send me a pm if you come across an extra set
thats interesting.. didnt know that.. send me a pm if you come across an extra set
oof... well... your f***ed. 
Uhm... become more patient?
I don't think my Dodge2500 spins much slower at 75 with 3.50's and 285's
Uhm... become more patient?
I don't think my Dodge2500 spins much slower at 75 with 3.50's and 285's
thanks for that helpfull insight
seriously though... you could try to track down 3.73 from a European wrecker. or spend the $$$ and buy direct from Dave at Japan4x4. The rear's are easy, as they share the same gear set as an FJ60 (which came in 3.73).
Or... you could graft an FJ60 axle to the front. That would be a _lot_ of work, but it would solve the 3.73 issue, you'd get a stronger front R&P. You could use the IFS rotors to gain the extra width needed (the FJ60 axle is 3" narrower or so). It has been done (albeit, under a mini truck... but he did use 80 parts).
but after all that work... 3.73 isn't much of a gain from 4.10 (I'm assuming you are running stock 4.10 gears).
sweet truck btw. I had a 4BT/NV4500/Orion in a 1994 80. used a mini-truck clutch pedal, gut down the stock pedal to match. The stick came up pretty far forward, like under the HVAC ducts. I ran 315's (35's).
some picts here:Picasa Web Albums - Brian - 4BT80 Project
Or... you could graft an FJ60 axle to the front. That would be a _lot_ of work, but it would solve the 3.73 issue, you'd get a stronger front R&P. You could use the IFS rotors to gain the extra width needed (the FJ60 axle is 3" narrower or so). It has been done (albeit, under a mini truck... but he did use 80 parts).
but after all that work... 3.73 isn't much of a gain from 4.10 (I'm assuming you are running stock 4.10 gears).
sweet truck btw. I had a 4BT/NV4500/Orion in a 1994 80. used a mini-truck clutch pedal, gut down the stock pedal to match. The stick came up pretty far forward, like under the HVAC ducts. I ran 315's (35's).
some picts here:Picasa Web Albums - Brian - 4BT80 Project
and with that ratio and tires you'd be running 1800rpm at 70. big difference with a 12 valve
thanks, i used the clutch pedal from the dodge donnor truck, just kinda fabbed a pivot point. the shifter actually came out in the perfect place... because of the extra 2 cylender i must have put mine a little farther back..
Tapage
Club 4X4 Panamá
you really need more than 70mph . ?
I would add bigger tires like true 37" and call it done ..
.002 cents
I would add bigger tires like true 37" and call it done ..
.002 cents
Jason Andrews
Modaholic
X2!!!!!This is the much simpler, cheaper, and better idea.
I don't have a tach but I run higher rpm than that. I have 4.88's, 37's, and have a manual lockup overdrive. It is fine to drive at that rpm all day it just wont get the best mileage there. Mine sounds best at about 64mph so I know how you feel about it spinning fast at 70 or 80mph.
Where are you located at?
had the same idea with the bigger tires but the help would be minimal... in the area of 2mph at 75
and i dont need to go faster than 70 but if i do over 65 my mpg drops from around 22 to about 17 because of the rpm. and i just dont like running the motor that high that long so i avoid long highway trips
and i dont need to go faster than 70 but if i do over 65 my mpg drops from around 22 to about 17 because of the rpm. and i just dont like running the motor that high that long so i avoid long highway trips
oh and i'm in the kansas city area
Im almost in the same boat as you, though 37's do help a fair bit, I will do about 70 mph with mine.
The other option $$$ is the 8% higher split case gears from advanced adapters, though they run close to $2K. Other than that diff gears suddenly dont sound so bad, stock dodges are around 3.54 or so for a comparison.
Jason Andrews
Modaholic
Same boat here. I can get about 22 if I keep it between 60-65mph. But who can do that on a long trip. If I do 70 I get down to the 17-18 range too. The short answer is 40's!!!!!!!! 
good to hear from you again cousin!! been a while... I am sure I could get a way to ship it here...
how much do they run? $$$
Not sure, but I can do some checking for you.
If you get a chance. I would like to get a ball park anyway. thx
No problemo, soon as I can catch the folks I need to talk to, I will let you know. I'm 1/2A$$ interested myself anyway!
1HD-T into a FJ80, along with the rest of the HDJ81 bells and whistles
https://forum.ih8mud.com/diesel-tech-24-volts-systems/408506-hdj81-guts-fj80.html#post6071359
https://forum.ih8mud.com/diesel-tech-24-volts-systems/408506-hdj81-guts-fj80.html#post6071359
