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Liquidforce · 03-13-2017, **(Subject: CM871 vs CM2250 bottom end )**

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.

Rawze · 03-14-2017, **(Subject: CM871 vs CM2250 bottom end )**

(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.

Mr Hagg · 03-14-2017, **(Subject: CM871 vs CM2250 bottom end )**

The short block we just had was a newer block like the 2250. There was no lower liner support...

Liquidforce · 03-14-2017, **(Subject: CM871 vs CM2250 bottom end )**

Thanks Mr Hag, perhaps I should have worded it slightly differently, if someone took a 2250 in frame kit, could it be installed in an 870/1 block, reusing the crank and block only? Then re-using all the 2250 ancillary parts installed on it. As we discussed via PM I'm looking at a truck that's had its engine let go due to ceramic plungers and have the opportunity to pick up a complete 871 cheaply, was looking at it for cheap insurance in case the 2250 motor had spun a main.

Running rough · 03-14-2017, **(Subject: CM871 vs CM2250 bottom end )**

(03-14-2017 )Rawze Wrote:
(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.

it would be interesting to know the compression ratio of my cm2250 cpl3606, i have heard the 2350 engines run at 18.9 to 1 ratio and i heard the new x15 effiecty series runs at 19.7 to 1, that is quite high, i belive 870 and 871 engines run at arount 17 to 1 while the austrailian isx e5 cm2250 runs around 17 to 1 compresion as well

Signature620 · 03-14-2017, **(Subject: CM871 vs CM2250 bottom end )**

The bores, journals, deck, etc are exactly the same as an 871 block but the 2250 and 2350 blocks have extra external mounts and threads to suit new components. 2250 overhaul kit will go straight into an 871 block but you may have issues mounting things like air compressors and fuel pumps to the block.

hhow55 · 03-14-2017, **(Subject: CM871 vs CM2250 bottom end )**

Another fine thread filled with great info from the the VERY BEST MINDS.

Rawze · 03-14-2017, **(Subject: CM871 vs CM2250 bottom end )**

(03-14-2017 )Running rough Wrote: it would be interesting to know the compression ratio of my cm2250 cpl3606, i have heard the 2350 engines run at 18.9 to 1 ratio and i heard the new x15 effiecty series runs at 19.7 to 1, that is quite high, i belive 870 and 871 engines run at arount 17 to 1 while the austrailian isx e5 cm2250 runs around 17 to 1 compresion as well

2250 is 17.4:1 (some documents say 17.3:1). blanket statements simply 17:1 - They respond like they are 17.4:1 so that is what I go by.

871 and older compression ratios have never been widely publicized. It is close to the 2250 but definitely responds like it is a bit less overall, hence the low-end torque response is not quite as good on them. I would bet it is 16 something, and this is what the tuning on them reflects too. Newer documentation says 17:1 but it is mostly a blanket statement. - I was told it is more like 16.3 from an ex-instructor but am not sure I trust that 100%.

Liquidforce · 03-14-2017, **(Subject: CM871 vs CM2250 bottom end )**

Thanks Signature 620, I assume no great issue in re-using the 871 air pump, but obviously fuel pump would pose an issue, no-one by chance happens to have both pumps sitting around.

I see a number of wreckers advertise the blocks as non- egr, or egr onwards, I wonder if it's mis-information on there behalf or it's workable.

Do the 871 have the external mounts but just not drilled/tapped? I can't imagine cummins would have retooled the block extensively to go to common rail.