CM871 vs CM2250 bottom end

[Rawze]

(03-16-2017 )Running rough Wrote:  ...
my 2250 is running soi increment at 3 with a 600 2050 cal, with the 871 turbo,
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I would be very careful of this. Even though the efficiency goes up, I would be very cautious of injector spray angles on the 2250. they are much wider than a 871 and you could cause problems real fast by advancing the timing by very much. The best way to tell where you are at is to pull the injectors out of an engine that has run at a specific place for a while and see what the shadow on the pistons look like. If they are up at the outer edges of the bowl, you are pushing your luck. I.E> you can only get away with so much before high risk sets in. it is NOT just simply soi vs compression ratio vs other factors. All the mechanical traits come into play too.

In this picture, the engine was set for a master SOI offset of 8.0 on a CM871 that had the smaller injectors. The rest of the injection mapping was factory stock. It ran like that for 700k miles and it never caused an issue but it was at risk. On its own it was still safe, but if it had an injector that had gotten clogged, and the spray pattern had changed, it very well could have washed out a liner. The fuel mileage gains were very high from doing this, a solid +2-3 mpg but at what risk?. - Sometimes better is not always better. Too much of a good thing can get you.

(03-16-2017 )Running rough Wrote:  my question is what is the stock soi at low ideal 700 rpm for this engine
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I am assuming you are still referring to the 2250 you have the 871 turbo on. - if you want to find this out then watch the live fuel flow into the engine and manually adjust the injection mapping. You will find a point where the mg/stroke is minimized and it uses the least amount of fueling. You will also find a place where the valve-train starts to become very loose (you can hear it). - Best place is to be somewhere between these 2 for optimal idle. You can get away with this and not not worry about spray angles etc. because you have no torque load much on the engine. It will not hurt it a bit, but you had better believe as you go up in torque load that it will all change. You also have to start considering all the mechanical aspects like spray angles, lash etc. too once you move away from idle.

BTW: the 2350 is even worse. Spray angles are very high on them and you can't get away with s$it on them to optimize much at all. Those idiots with the big-name tunes are killing these engine with their added +12 degrees bulls$$it to the soi. It is downright ridiculous!.