Leaving an engine running?

[JimNiki]

Originally Posted by Auturbo6

Has to do with the size of a given piston when cold, or not at operating temperture. Certain pistons tend to shrink more when cold, requiring more time to get to correct size within the bore. However much more able to handle combustion processes from that point on. Some highly worked engines can sound horrible on cold start up.....

the hypereutectic pistons have a higher silicone content as opposed to normal
Silicone resists the shrinking/enlarging with temperature changes.

But too much makes them brittle...
I think they're about 16% instead of the normal 10-12%