Post by
Darius »
https://forums.nicoclub.com/darius-u5470.html
Tue Mar 20, 2007 4:52 am
If you are running a stainless manifold or an OEM organic gasket, stainless fasteners will be fine. If you are running the stock manifold with a copper gasket, the stainless fasteners will experience more thermal expansion than the manifold will and the seal is effectively loosened. In the realm of short fasteners, the thermal expansion difference between cast iron and stainless, assuming a 1200 degree F, is small. From my rough calcs, it is about 0.40mm which could be significant if there is no play in your gasket.
Moral of the story, stick with steel fasteners because they expand more closely to the cast iron manifold than stainless.