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That was the factory spec stud installation for those years of naturally aspirated cars.
Steel upper head studs, Dilavar lower.
Porsche said it was because the lower got hotter next to the exhaust and expanded more than the top next to the cooling fan. To even it out the clamping force, they used steel top, Dilavar lower.
I think they were experimenting.
I would use 993 Dilavar studs all around.
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1971 911S, 2.7RS spec MFI engine, suspension mods, lightened
Suspension by Rebel Racing, Serviced by TLG Auto, Brakes by PMB Performance
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