I have an '87 Rockwood Motorhome with a chevey 454 cu inch engine (4-brl) and 3-spd auto. The unit makes 5 mpg or less. I am thinking of swaping a 5.9L 12V with dodge automatic into the unit. Does anyone know if the Cummings would fit where the 454 is currently residing? Any and all information would greatly be appreciated.

Rob Lewis aka stargate2112

 

Try here
http://www.cumminsdieselspecs.com/12v.html

 

Rob drop the g in cummins it will save you some Grief! Good luck with the project

 

You may also need to reduce the axle ratio or find yourself limited on travel speed. These Cummins will run all day long at 2,007 or so, but cannot reach the 4,000 plus of a gasser.

The Cummins can run all day with the pedal buried while the gasser will blow in far less time than that.

 

Hey Thanks BigIron70 that link was very helpful indeed.

 

Thanks Grey Wolf it was a slip on my part

 

Hey Thanks for the information WestTN how much of a change would I have to make to be the same mph as a gasser? I haven't been under the motor home yet to check what gearing I have. But for ***** and giggles if I were to have say 410's I would go for what say 325's? or would it be a bigger change yet?

 

If you're looking to swap in an o/d equipped Dodge auto behind it I'd leave the gears alone and see how it does. The Cummins is pretty forgiving of tall/short gears. How much does the RV weigh? Do you know what RPM you spin at a given speed with what size tires? If you have 4.10 (probable) I'd say you're good. O/D is sorta deep, depending on which auto you go with, so taller gear ratio and a bunch of weight behind it may not be best.

 

To give a good recommendation we really need more info. What type of motor home is it class c or a? At 5mpg I am guessing its a class a. Thats what my dads was and it got 5mpg also. It turned around 3 grand at 60 or 65 do not really remember.I think it had a 4:56 ratio . You need to know what size tires you have as in how tall and then you can use a gear ratio calculator to determine what gears you want. If it is a class a I would put a motor combo out of a med duty truck with its auto I think they are Allison's then just gear it to the rpm you want in hi gear I find that mine has a sweet spot starting around 2200 up to 2700. Thats for pulling the trailer in overdrive my speed is about 60 to 70.