CM871 Engine cycle...

[Texasdude74]

(12-24-2016 )Rig Wrench Wrote:  What does the higher boost (40+psi) do that causes the damage to the engine? Particularly the Isx. What is the few extra pounds of air pressure doing to cause damage. I understand overspeeding the turbo, but other brands of engines survive at higher pressures, and competition engines often much higher. I've heard of cm870, 871 and 2250s running upwards of 46 psi for hundreds of thousands of miles, although most of them have fixed vane turbos. I'm in no way endorsing it, just tryin to understand.

My understanding is there are two theories on turbo diesels: lower compression and bigger turbo or higher compression and smaller turbo. High compression engines build high cylinder pressure with less boost. Too much boost quickly leads to too much cylinder pressure. Which causes all sorts of bad things. Too much heat, pre ignition, hammerd rod bearings, blown head gaskets, cracked heads etc.

Either of the two methods of engine building have their own merits. Low compression, big turbo setups need a moderate boost level constantly to run efficiently. If you never really load the engine much, it's probably not for you.
I've heard engine builders claim the low compression motors are better for drivers that won't "get off it" and high compression motors are better for guys that "won't get on it."