Ash content corrolations to Pre-Ignition

[joff]

Very interesting thread.

Any speculation as to why oil ash content causes higher preignition? Is it because of the ash in the exhaust->intake carry-over volume due to the burning oil in the expansion/exhuast strokes?

Compare that to oils that have relatively high ash contents (1.2, 0.9) which experienced their first pre-ignition event within 8 cycles.

Preignition within 8 cycles??!! I doubt many people have paid that much attention to oil ash content in the past -- how can there not be more blown motors because of this?