[bpick84]

To answer your question on valve expansion, all metals expand and contract with temperature change. Expansion is viewed in a linear change in length. Therefore, a valve would expand in length and in diameter. Since the diameter is proportionally smaller than the length, the expansion is not as noticable. Expansion is figured by using the coefficient of linear expansion. For mild steel it is 0.00065 inch per inch per 100F temperature change. Stainless steel is 0.00099. I am not sure exactly what the metal is in a Porsche valve, however the exhaust is sodium filled for heat transfer. To figure exact length change would be difficult due to heat transfer. More than you wanted to know and still no answer.