First, there ain’t no “G” in Cummins.
There are three common engines in a school bus: Cummins, International, or Caterpillar.
All three companies put out great mid-size diesel engines and generally are able to achieve 200,000 miles before doing an overhaul. Caterpillar no longer makes on-highway engines and the price of parts is quite expensive, but generally of high quality. While the International DT466 is a legend in it’s own right, we usually stick to Cummins in most applications for ease of maintenance, durability, and parts affordability. There are two sizes available from Cummins in the years we like: the 5.9L motor and the 8.3L motor. The 5.9 is a quick, peppy, and versatile motor that is also found in Dodge pickup trucks, while the 8.3 is an absolute power house, making up to 285 HP and featuring a wet-sleve design that allows for in-frame engine rebuilds, saving you time and money when the time comes. We recommend these motors:
5.9L Cummins 190 - 230 HP
8.3L Cummins 250-285 HP
7.6L International DT466 180-250 HP
As far as your transmission they are generally all automatic and all Allison automatic transmissions. There are three models we recommend:
MT 643 (all-mechanical 4-speed, no overdrive)
MD 3060 (computerized 5-speed, w/ overdrive and unlockable 6th gear for double o.d.)
2000 series (computerized 5 speed, w/ overdrive)