4.56 Gears Behind a Cummins
 

Hey Guys , Parts gathering is going well for my suburban conversion , I just picked up a set of rears , dana 60 for the front and a 14 bolt for the rear , I just have to do a yoke swap to the 1410 .
The rears are out of a M1008 Military k30 SRW with 4.56's and a detroit locker ... that have 28K on them and look like new .
I have the motor , its a 2nd gen out of a 1995 dodge , I also have the trans , NV4500 with all the upgrades mounted to a 93 NP 205 right side drop .
I'm going with a 36" tire , not sure if the 4.56 are going to be a bit steep for the cummins , but with that size truck I'm happy cruising 65 , I know the mileage may suffer a little with that gear ..
Dose any one have the rpm calculation for my combination .

Thanks

going to be steep. go with a 37" tire and will be good. i am at 1850 rpm going 80 with my 37's and 3.73 gears (just to give you an idea)

What kind of tires ? I'm doing a 6" lift so there should be room .

i have toyo 37x13.5x20 open country mt's. had 40's on it for the last year and was going 90mph @ 2000 rpm. but lagged the heck out of it at slower speeds.

Using the tire diameter of 36" and circumfrence of 113.10 or so and 4.56 gears, it looks like 66mph with the NV4500 tranny in OD will be 2100 rpm.

Dave

Thanks Dave , Thats not too bad ... especially if I am hauling a trailer ... I'm up in the air on the lift and tire size right now .
I did find a SRW dana 80 but it has 3.54 gear and thats going to be a little low with the 36 or bigger tires , then I will have to do a gear change on the front and rear .
I don't mind going bigger , I was considering going with the big truck tractor floats but even with hydroboost those wheels and tire comb have way too much rolling mass ... I had them on another truck .
I'm going to hang on to what I have and just plan on maybe a little bigger tire to get the RPM down rather then a gear change .
I know the Toyo's are a good tire and have good load rating ... thats my main consern with the bigger tires , I know Ground Hawg has a radial 36 " tire with a good load rating .

2100 is the rpm you want to be at for towing. If you go below that, you might have some issues with EGT's.

I may put some 4:56's in my truck later on when all I'm doing is towing my fifth wheel. What I need is 4:30's. No one makes them. 4:10 only gets me
200 rpm above the 3:73's I currently have. Need to get the load off that 48RFE tranny to make it last. Less tranny temp, lower egts.

Good luck with your project.

Dave