Quote:
Originally Posted by winders
Except 993 Turbo head studs (dilavar) seem to work really really well. Many of the high output 3.6 to 4.0+ liter race engine builders exclusive use the 993 Turbo head studs. I am not saying the SuperTec studs aren't great, but it seems odd to put all dilavar heads studs in the same bucket when the 993 Turbo parts work great.
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993 turbo studs are lumped in with "all" other Dilavar studs for one simple reason: Metallurgy. The redesigned 993 stud (all-thread) helped prevent breakage but did nothing to change the underlying flaw in the material. Inconsistent clamping force based on environmental changes. The reason Porsche tried so hard to make Dilavar work had very little to do with cylinder to head stability and everything to do with warranty mitigation. Horizontally opposed air-cooled engines tend to leak oil from the head to cylinder joint, especially during cool-down.
The instability during full temperature running is always appearance on tear-down.
Clamping pressure when cold translates to a higher clamping force at full temperature. Engineers can easily calculate that force when dealing with constant numbers. As the engine expands, clamping forces should/do increase. With an engineered steel stud, that clamping force is magnitudes more consistent than you get with the ever-changing Dilavar. This inconsistency causes the cylinder to head joint to fluctuate creating poor sealing and unnecessary internal stresses.
Two simple questions: Why were the first 993 turbo studs made from steel? Why, if Dilavar is so magical, did Porsche move to steel studs in the GT3 Mezger based engine?