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The Four stroke cycle of the CM871 Engine...

TDC = Top Dead Center (top of piston stroke).
BDC = Bottom Dead Center (Bottom of piston stroke).

BTDC = 'Before' Top Dead Center
ATDC = 'After' Top Dead Center

In a four stroke cycle engine, four strokes of the piston are required to complete one cycle. The four strokes are...

Induction -- Clean air is pushed into the cylinder from the turbocharger (intake). The induction stroke starts when the intake valves open 10° before TDC, then air is drawn into the cylinder as the piston moves down. The inlet valve closes 1° before BDC.

Clean Air is Sucked In...


Compression -- The air is now trapped in the cylinder and as the piston rises on the compression stroke, the air is compressed. As the air is compressed, it rises in temperature.

That Air is then Compressed...


Power -- When the piston reaches about 19° before TDC (Adjusted by the ECM), the injection of fuel commences and continues until about 73° after TDC. The heat in the compressed air ignites the fuel and combustion takes place. The gases expand forcing the piston down, providing power.

The Piston Fires...


Exhaust -- The exhaust valves opens at 26° before BDC and the exhaust discharge as the piston rises again. Most of the exhaust gases have been discharged as the piston nears TDC. However, at 10° before TDC, the inlet valve opens to start the next Induction cycle. The rush of air that enters the cylinder, helps discharge any remaining exhaust gases until the exhaust valve closes at 3° after TDC.

Exhaust Gas Escapes...


As the next Induction cycle start, of coarse, The whole cycle is repeated.

The result, is that Power is only produced by any given piston every 'Other' cycle of the engine. This also means that for every two rotations of the crankshaft at the bottom, there is only one rotation of the camshaft(s) at the top (in the head).
Do you have one that explains the "sweet spot" of crank angle?
On my 2250 when I {**removed by protection bot**} it we also did a 4 degree timing advance, and it had pretty much instance torque response even at 1200 rpm, this is on a stock 2050 torque engine, seems like advancing the timing makes faster response, but be careful you do not want to advance it to much as it can cause severe engine damage, I am not saying that a 4 degree timing advance is bad on a stock cal, it all depends on where the stock cal already is, but I do know this with @m*m^2 and 4 degrees advance timing my oil did not get black anymore, it stayed clean a lot longer, however I had a slight vibration below 1400 rpm and we put the timing back to stock to see if that will cure the issue, but I do remember it kind of did the same thing with all the crap on it, just not as noticeable, could be the clutch or steady bearing or anything really, because I know there are isx's out there putting way more power and torque down then mine and apparently they do not vibrate when lugging down, but I wana be on the safe side, however like I said before driving it with 4 degrees timing advance makes it feel quite a bit more powerful and responsive
When I say vibration I mean only under full torque conditions
on a 2250, Boost above about 36 + psi or so and heavy torque would cause it too. They have a higher compression ratio than older engines and require less boost to produce the same power. If you are above 35-36 psi or so, I bet if you back off on the boost a little bit, it would go away.
Right because my boost peaks at 40 to 42 psi, before {**removed by protection bot**} it was around 38 with the egr monster
Sounds like you need to get that lowered right away. I would get with whoever programmed it and have it adjusted. In the mean time, just keep it under about 36 or so.
I don't have CM2250s but I did set my CM871s to 30 lbs boost and they purr like kittens, I would also recommend that you back off the boost a bit as well.
(03-15-2016 )in2trux Wrote: [ -> ]Do you have one that explains the "sweet spot" of crank angle?

This!! I'd love to have a better explaination/understanding of this crank angle stuff in simple man terms
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