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Old 06-19-2012, 08:12 PM   #1
Join Date: Sep 2006
Location: Northwest
Posts: 15
Year: 1973
Coachwork: Superior
Chassis: International
Engine: 392 gas International
Rated Cap: 65
Engine swap from a 392 gas to a 5.9 Cummins

I would like to swap my 392 International gasser for a 5.9 Turbo Cummins to improve fuel mileage. I get around 7 mpg right now with a manual 5 speed, and would like to get it up to around 12 or 13. If I can't get it somewhere in that neighborhood I will have to rethink the whole idea of converting my schoolie. My VW diesel Jetta gets around 40 mpg even hauling my teardrop trailer, so it makes me cringe to go anywhere in the bus.
Does anyone know if this is a fairly common swap? I understand I will have to change the rear end ratio also. If you know of any common pitfalls or expensive gotchas please let me know.
It don't make no sense that common sense don't make no sense no more. - John Prine
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Old 06-20-2012, 05:02 PM   #2
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Join Date: Oct 2005
Location: Clearlake, Northern California
Posts: 1,751
Year: 1992
Coachwork: Blue Bird
Chassis: TC-2000 Frt Eng, Tranny:MT643
Engine: 5,9 Cummins
Rated Cap: 84
Re: Engine swap from a 392 gas to a 5.9 Cummins

No, I believe such swaps are much talked about and seldom completed. If you are getting 7 MPG with gasoline you are doing very well. Mine got around 4. The stick shift no doubt helps, compared with the AT545 automatic I had. Getting 12 MPG with a diesel may be doable, but don't count on it.

If you do pursue this, I suggest you buy the engine and manual tranny as a compete unit out of a commercial truck -- with crossmembers and everything you will need. And the rear end at the same time. But Dawg, you can buy a lot of gasoline for what this would cost.

My hunch is you'll be better off scouring the country for a diesel bus with stick shift.
Millicent The Bus - roof raised two feet, toy-hauler tailgate.
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Old 06-20-2012, 11:29 PM   #3
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Join Date: Oct 2009
Location: Moodus, Ct.
Posts: 969
Year: 1996
Coachwork: Champion
Chassis: Ford e-450
Engine: 7.3 Powerstroke
Rated Cap: 14
Re: Engine swap from a 392 gas to a 5.9 Cummins

Its relatively common to swap a Cummins into Ford pick ups nowadays-so there will be alot of "standalone" info about rigging up the computer to behave when not hooked up to the donor Dodge truck.
Don't make a fuss-just get on the bus!

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Old 06-21-2012, 04:23 AM   #4
Join Date: Jul 2011
Posts: 124
Year: 1999
Coachwork: ElDorado
Chassis: Chevy P30
Engine: 7.4 liter 454 Chevy
Rated Cap: 24
Re: Engine swap from a 392 gas to a 5.9 Cummins

Just remember type of cummins 5.9 you get.
Early ones had what was called the "dowel pin of death"; a dowel pin inside of the timing cover would walk out of its hole in the block and eat the timing cover and gears. They have a fix to make a metal tab to cover the dowel's end so it would not move. ... ewall.html
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