Do you mean #993.101.170.53 and if so, what material are they?

Head Stud Mfg.
 

Chris
When will your first batch be ready?

Mike Curnow

hummmm wonder if the threaded part allows expansion to match the cylinder expansion when heated or the threads allow stud expansion without breaking?

Mike, I am not sure that I am brave enough to take this step just yet :D

I don't think that the overall forces will change once the engine has reached a stable operating temperature as the threads won't affect the expansion of the stud once it has reached this equilibrium temperature.

I can imagine that there could be a peak level of clamping force due the temperature difference between studs and cylinders whilst the engine is warming.

It is interesting to consider that the increase in surface area created by the threads could influence the time for this equilibrium to be reached and reduce the force created by this difference.

This would be a very subtle change and Dilavar is likley to have a much lower level of thermal conductivity than a conventional steel stud so warm up time to reach equilibrium would be longer.

The other Stainless Steel and Nickel Alloy Studs - Casper Labs, Supertec and ARP, would also have lower conductivity and are not fully threaed.

There is a theory that very closely pitched and fine concentric grooves in the parallel portion of a test bar can increase the yield strain measured during a tensile test.

Post yield these grooves have no impact on either elongation at failure or Ultimate Tensile Strength.

Although threads do resemble concentric grooves a 1.5mm pitch is much too coarse to create this effect.

If, as I believe, Dilavar studs normally fail due to SCC resulting from interganular corrosion then increasing surface area could have a negative influence as more grain boundary will be exposed to the environment but I think the surface treatment is designed to eliminate this type of failure.

The basic idea is certainly worth more thought. :)