Swapping Detroit for CAT or Cummins

I don't have to i have done it many times. You drank the kool aid and won't be swayed. Your smarter than me and I don't care.


Use the search box it's all there


Do a little research about why they don't come in high horse applications. Learn about side load pressure inside the diff from a extrmely large pinion and axle twist

 

Because you will twist drive shafts in the lower trans gears.
As mentioned, rpm plays into this equation. Not just engine rpm, but component rpm. A slower rotating drive shaft will have a much higher torque load than a faster rotating drive shaft.
A 4.10 r&p will break axle shafts faster than drive shafts, where a 2.67 will break drive shafts before an axle shaft.

 

It is all about startabilty or lifting off with big weight. That's why people don't spec 2.70 with big horsepower. You'll twist the drive shaft off before movin a wheel.. also the smaller the crown and pinion (taller gears ) the weaker the rear end. This is why you see average gravel trucks , lowbed trucks and logging trucks with big power and 4:10,4.33 Or 4.63. Gears.

Having said that I agree with Benjamin,
The difference between a truck with 4:63s and one with 3:55 about a full gear in transmission. They both pull the hill same speed.

 

To "downspeed" correctly, your engine, clutch, trans, driveshaft, and rears all have to designed for it. Seems newer engine torque band is lower and smaller, so you need close steps in top gears for the hills. Downspeeding is only good for certain applications like light loads and flatter terrain.

 

But dude how do you know the truck is making from 6 to 9 mpg . now im more confused

 

A DD14 ? i though cummins make more than 7 MPG. Someone out there help. LOL

 

I'd say giver. If you up to it an want a challenge get it done. I swapped a dead n14 for a 3406b took 2 days an minimal cash.

 

Their easy 2 days with some get it done attitude. Had a dead n14 swapped it with a 3406b in a 90 T800 their designed to interchange an for not much cash

 

1987 freightliner with a turned up 310 cat 13 speed pulling 53' tri thru hills hauling straw. Propane boost I got just over 9 mpg on 7 round trips on a day average. Sounds rediculous bit that's wat I got. That truck is used to 40-50 ton loads so that's why I added propane boost an wat a difference.

 

Help me out here because I'm stupid.

Lets say in your example, the truck with the 3.70 rear has a 13 speed and needs to drop to 10th gear with 11R24 rubber to pull the hill.
1. What is the final drive ratio required to pull the hill?
2. What gear will truck with a 2.70 rear have to use to get the same final drive ratio as truck #1?