Ed_Moorman:

Thanks for the answer and the link for the web site. That's what my friend was talking about.
When you said to heat piston to 350 degree, do you mean Farenheit or Celsius?
What about the cooling? Rapidly, by quenching on water or oil or cooling it slowly? Any "aging" after that? I mean, heating it again to a lower temperature for 20 to 30 minutes.

Some understood I was asking about expansion with temperature, sorry but this was not the question. I meant growth, piston actually increasing diameter after being cool again.

If I knew this would be true we wouild take an old low compression ABC piston/sleev set and would do the experiment.
But need to have an idea if this really happens and which temps, cycle, aging and time is needed (aproximate).
I found a tread on another forum talking about changing hardness on aluminum alloy and it seems there are some sort of phase setting with the additional chemical elements added to Al.

Sharp333