Forged pistons, silicon content and sidewall clearance

[mgeoghega@radford.edu]

I have been doing some research on forged pistons lately. Does anyone here run
them? If so, what kind and what kind of sidewall clearence do you run? Stock
is .010 - .030 mm, or .0004 - .0012 inches. I see that there are two common
alloys, 2618 and 4032. The 4032 alloy has a higher silicon content (12%), so
you can run a tighter sidewall clearance. I am just wondering how tight? I was
first turned off by forged pistons because of the large clearences neccesary,
which result in increased wear. I need this motor to last for a long time, so
anything with a high thermal expansion is out of the question. Btw, since the
4032 is 12%, does that make it eutectic, or is the percentage number of what is
hyper/hypo eutectic not set in stone because of the effect of the other
elements in the alloy? I am also wondering how strong the 4032 is compared to a
2618 alloy and also a stock cast piston.
Also, I have read of tuning the thermal expansion rate of the cylinder wall
with the piston. Anyone have any good info on this? TIA

-Mike