CM871 vs CM2250 bottom end

[Rawze]

(03-13-2017 )Liquidforce Wrote:  Aside from the head differences (DOHC/SOHC) is a CM870/1 bottom end (block/crank) the same as a CM2250? Basically could you use a 871 base to build a 2250 motor, looking at a truck that's had ceramic plungers and has taken out the motor so trying to work out the most economical way forward with it.

Although the block itself may possibly be compatible, the pistons, etc are different. Not even the compression ratio is the same. This means there is no program for either an 871 or a 2250 ECM that would be compatible. The programming alone would have to be build from scratch if 871 pistons ect were used with a 2250 ecm and head or vice versa.

I have made a couple custom programs for engines where they use a 2350 base or engine to replace a 2250, keeping the all the external 2250 wiring and components. Cummins themselves did one under warranty (no 2250 engine available at that time) where they used a 2350 engine to replace a 2250 for a guy and could not get it to run quite right. It ran but had poor fuel mileage, oil ran hot, and it had a lot of other minor issues. -- They never did figure out what was wrong and it. - It ended up being sent to me to have it custom programmed. It was no easy task to get it right, but after, it ran beautifully.

Again, it was a case of different compression ratio and different internal components. Since it was an entire engine, even injectors were very different with different spray angles and patterns. It was basically a 2350 engine with all 2250 wiring harness, etc. for a truck that was 2250 originally. There is a lot of custom ECM work that needs to take place for it to run right.

I just did another one this past week for a guy. It was a 2250 that got replaced with a 2350 engine form a wrecked truck, keeping all old wiring and old 2250 ECM. It was no easy task to get it right either, but now it runs great.